Early Optical Follow-Up Observations of Einstein Probe X-Ray Transients During the First Year

Abstract

We present early follow-up observations of Einstein Probe (EP) X-ray transients, following its first year of operation. EP is a dedicated wide-field X-ray observatory that is transforming our understanding of the dynamic X-ray universe. During its first year, EP successfully detected a diverse range of high-energy transients—including gamma-ray bursts (GRBs), tidal disruption events (TDEs), and fast X-ray transients (FXTs), besides many stellar flares, disseminating 128 alerts in the aggregate. Ground-based optical follow-up observations, particularly those performed by our BOOTES telescope network, have played a crucial role in multi-wavelength campaigns carried out so far. Out of the 128 events, the BOOTES Network has been able to follow up 58 events, detecting 6 optical counterparts at early times. These complementary optical measurements have enabled rapid identification of counterparts, precise redshift determinations (such as EP250215a at $z=4.61$), and detailed characterization of the transient phenomena. The synergy between EP’s cutting-edge X-ray monitoring and the essential optical follow-up provided by facilities, such as the above-mentioned BOOTES Global Network or other Spanish ground-based facilities we have access to, underscores the importance and necessity of coordinated observations in the era of time-domain and multi-messenger astrophysics.

1. Introduction

X-ray transients represent some of the most energetic and dynamic phenomena in the universe, offering unique insights into extreme physics and fundamental astrophysical processes [1,2,3]. These events encompass a diverse range of sources, including tidal disruption events (TDEs), gamma-ray bursts (GRBs), stellar flares, and compact object mergers [4]. While X-ray observations reveal their prompt emission mechanisms, optical follow-up observations play a pivotal role in classifying transients, measuring redshifts, and constraining multi-wavelength energetics. For example, optical spectroscopy provides critical redshift measurements for cosmological GRBs [5], while color evolution in afterglows probes jet dynamics and circumburst environments [3].

The Einstein Probe (EP) mission [6,7] addresses the need for wide-field X-ray monitoring with its unique dual-telescope design: the Wide-field X-ray Telescope (WXT) surveys ∼3600 deg² per exposure in the 0.5–4 keV band, while the Follow-up X-ray Telescope (FXT) provides rapid (<4 min slewing) deep imaging with a sensitivity of ${10}^{-13}$ erg cm⁻² s⁻¹ in 2 ks [6]. EP employs two trigger systems: (1) onboard triggers for bright events (e.g., GRBs) and (2) ground-processed triggers for fainter transients (e.g., FXTs), leveraging real-time data downlink through the Beidou system [7].

This article focuses on optical follow-up observations conducted by the BOOTES Global Network [8,9,10] for EP transients during its first year of operations. BOOTES comprises seven robotic stations equipped with 0.6 m Ritchey–Chretien telescopes, achieving a slewing speed of 100 deg/s and a pointing accuracy of <5″ [9]. Each telescope utilizes SDSS $u^{\prime }{g}^{\prime }{r}^{\prime }{i}^{\prime }$ and WFCAM/VISTA $Z/Y$ filters, reaching limiting magnitudes of $m\approx 20.5$ in 300 s exposures [10]. In this work, we analyze the following:

• Time delays between the EP X-ray triggers and our optical observations.
• BOOTES’s observational strategies and site-specific performance.
• Case studies of high-redshift GRBs (e.g., GRB 240315A at $z=4.86$) and outstanding transients (e.g., EP240408a).

The synergy between EP’s rapid localization and the BOOTES network’s robotic response has been demonstrated in multiple events (see Table 1), where BOOTES swiftly carried out optical follow-up observations to complement EP’s X-ray detections. This coordinated effort not only enabled rapid identification of potential afterglows but also paved the way for deeper spectroscopic studies using facilities like the GTC (Gran Telescopio CANARIAS) or VLT (Very Large Telescope), thereby greatly enhancing our understanding of these transient phenomena. Conversely, the absence of optical counterparts for EP240408a down to $r>24$ mag challenges existing models of jetted TDEs [11]. These results highlight how optical follow-up not only complements X-ray data but also drives new theoretical inquiries.

Table 1. EP alert systems and BOOTES performance [6].

Parameter	Onboard Triggers	Ground Triggers
Energy Band	0.5–4 keV	0.5–4 keV
Brightness Threshold	>10−9 erg cm−2 s−1	>10−11 erg cm−2 s−1
Localization Accuracy	∼1′	∼30″

Section 2 details EP’s alert pipelines and BOOTES’s observational protocols (Section 2.1 and Section 2.2) as well as time response statistics and light curves (Section 2.3), while Section 3 discusses the astrophysical implications of key sources. Our findings establish a framework for optimizing transient follow-up in the multi-messenger era.

2. Methods

The transients analyzed in this paper were discovered by Einstein Probe (EP) between 19 February 2024 (the first source EP240219) and 26 February 2025. The data presented in this paper were compiled from various public sources, with a focus on optical follow-up observations conducted by the BOOTES network.

2.1. Data Sources

Our analysis focuses primarily on optical follow-up observations from ground-based facilities, particularly the BOOTES network. Key data sources include the following:

• The GCN (Gamma-Ray Coordinates Network) Circulars, which provide prompt notifications of EP detections, including source coordinates and discovery time (https://gcn.nasa.gov/circulars, accessed on 26 February 2025).
• The Astronomer’s Telegram (ATel) reports, which contain follow-up observations and classification information from various teams (https://www.astronomerstelegram.org, accessed on 26 February 2025).
• Published papers focusing on specific EP sources, providing detailed multi-wavelength analysis and source characterization.

For each transient, we compiled key information such as the following:

• Discovery time and position.
• Multi-wavelength follow-up observations, with a focus on optical data from the BOOTES network.

2.2. BOOTES Network Follow-Up Observations

BOOTES (Burst Observer and Optical Transient Exploring System) is a global network of robotic telescopes designed for rapid response to transient alerts. Its strategic distribution across seven stations enables near-continuous monitoring and follow-up observations of transient astronomical events.

2.2.1. Telescope Network

The BOOTES network consists of seven stations (B1–B7) located across different continents, as shown in Table 2. Each station is equipped with a 0.6 m Ritchey–Chretien telescope, designed with fast-slewing capabilities to respond rapidly to transient alerts.

Table 2. BOOTES network sites location.

Site	Latitude	Longitude	Altitude (m)	Location
BOOTES-1	37°05′58.2″ N	6°44′14.89″ W	50	Mazagón, Spain
BOOTES-2	36°45′24.84″ N	4°02′33.83″ W	70	Algarrobo-Costa, Spain
BOOTES-3	45°02′22.92″ S	169°41′0.6″ E	360	Lauder, New Zealand
BOOTES-4	26°41′42.8″ N	100°01′48.24″ E	3200	Lijiang, China
BOOTES-5	31°02′39″ N	115°27′49″ W	2860	Baja California, Mexico
BOOTES-6	29°02′20″ S	26°24′13″ E	1383	Maselespoort, South Africa
BOOTES-7	22°57′09.8″ S	68°10′48.7″ W	2440	Atacama, Chile

2.2.2. Instrumentation and Observations

BOOTES telescopes are equipped with SDSS $g^{\prime }$, $r^{\prime }$, $i^{\prime }$ and WFCAM/VISTA Z and Y filters, along with Andor iXon X3 EMCCD cameras that provide a ${10}^{\prime }\times {10}^{\prime }$ field of view. These telescopes can initiate observations within minutes of receiving an alert, ensuring timely multi-band photometry to capture the color evolution of transient sources. The limiting magnitudes vary based on telescope and exposure time, with BOOTES-5 reaching $m\approx 20.6$ mag in a 300 s exposure. The BOOTES network is also equipped with the low-resolution spectrograph COLORES [12] and has demonstrated its versatility in observing diverse optical transients, including gamma-ray bursts and stellar flares. Its rapid slewing capability (<100 deg/s) ensures timely follow-up within critical observational windows.

Data reduction includes standard procedures such as bias subtraction, flat-fielding, and photometric calibration using Pan-STARRS reference stars [13]. Differential photometry is employed to analyze the brightness variations over time.

2.2.3. Response Times and Observational Strategy

The response time for BOOTES observations varies depending on the alert type. Onboard triggers for the brightest transients typically result in faster follow-up observations, while ground-based processed triggers for fainter events may have longer delays. For instance, Stellar flares typically exhibit rapid variability with durations of 1–2 h at most, as evidenced by the multi-wavelength observations of the DG CVn superflare [14]. Monitoring the delay between transient onset and the first observation is crucial for understanding the transient’s early optical behavior.

2.2.4. Spectroscopic Follow-Up with 10.4 m GTC

Spectroscopic observations with the 10.4 m GTC telescope (+OSIRIS spectrograph) constitute a pivotal component of our multi-wavelength follow-up campaign. While the BOOTES network provides rapid optical imaging and initial photometric characterization, the high-resolution spectrum obtained here allows for a precise redshift determination and a thorough examination of the host galaxy’s environment. These spectroscopic data enable us to investigate the physical conditions in the host and along the line of sight, offering critical insights into the interstellar and intergalactic media. Such information is essential not only for confirming the nature of the transient event but also for refining theoretical models of its progenitor system. Among the various sources we observed, the transient EP250215a is of particular interest. As an example, we show in Figure 1 the two-dimensional spectrum, which reveals a pronounced spectral break at ∼7100 Å, attributed to Ly$\alpha$ absorption.

Figure 1. Two-dimensional spectrum of EP250215a obtained with GTC/OSIRIS. The red continuum remains smooth up to ∼7100 Å, beyond which a pronounced spectral break appears. This feature is attributed to Ly$\alpha$ absorption in the host galaxy’s interstellar medium (ISM), while the blueward region is characterized by a Ly$\alpha$ forest produced by HI absorption from intervening intergalactic medium (IGM) clouds along the line of sight.

In summary, the integration of fast-response imaging and detailed spectroscopic analysis exemplifies the comprehensive approach needed to unravel the complexities of these transient phenomena.

2.3. BOOTES Responsiveness

The BOOTES telescope network excels at rapid follow-up of astronomical transients, delivering near-real-time optical observations. Figure 2 breaks down, for each EP trigger, the interval from trigger to formal report (“Trigger → Report”) and the ensuing BOOTES observation. Remarkably, in 53 of 113 cases (46.9%), BOOTES began observing before the formal report—i.e., negative tracking delays. To achieve millisecond-level ingestion and parsing of EP alerts, BOOTES relies on the GCN Kafka service (built on Apache Kafka [15]). Kafka’s high throughput allows the network to autonomously schedule observations even before GCN Circulars are issued, underpinning the “negative latency” measurements in Figure 2 and enabling capture of the earliest optical light curves. Figure 3 illustrates the response time distribution of the BOOTES network; fifteen logarithmically spaced bins were used to generate a normalized histogram of BOOTES response delays (in hours) on a logarithmic axis, highlighting the skewness of the distribution, demonstrating its exceptional capability for rapid follow-up observations of transient events, with the majority of observations commencing within the critical first hours after detection.

Figure 2. Time delays of BOOTES telescope network follow-up observations for EP transient sources, plotted on a logarithmic time axis (hours). Each horizontal bar is composed of up to three segments: (1) Trigger → Report (blue), showing the elapsed time from the EP trigger to the formal report; (2) BOOTES Follow-Up (After Report) (green), representing observations initiated after the report; (3) BOOTES Follow-Up (Before Report) (red), indicating negative tracking delays when BOOTES began observing prior to the report. Bars are offset from the origin by a small constant (left = $1\times {10}^{-4}$) to ensure visibility on the log scale. This chart highlights BOOTES’s rapid-response capability across a wide dynamic range of follow-up latencies.

Figure 3. Distribution of BOOTES response delays to astrophysical transients initially detected by the EP telescopes. Despite the challenging slew and setup, BOOTES achieves follow-up within 1 h for 13.3% of triggers and within 3 h for 22.1% of triggers, capturing the crucial early-time emission before most observations begin.

Figure 4 shows the earliest optical detections and upper limits for EP sources observed by the BOOTES telescope network. The heterogeneous distribution of data points reflects the varying sensitivity and response times of the BOOTES telescopes. For example, the repeated observations of EP240426a by BOOTES-4 and BOOTES-6 demonstrate the network’s capability to track transient evolution across multiple instruments.

Figure 4. The earliest optical detections and upper limits for transients observed by the BOOTES telescope network. Magnitude values (or upper limits) are plotted against the time difference $T_{\mathrm{start}}-T_0$ (hours), where $T_0$ is the initial trigger time. Data points are categorized by the BOOTES telescope identifier (BOOTES-2 to BOOTES-7), with empty markers indicating upper limits. Vertical dashed lines highlight special cases: a rapid brightness drop of 1.9 mag (red) and a 0.8 mag decrease (blue). The horizontal axis spans $-5$ to 80 h, and magnitudes range from 16 to 24.

BOOTES Network Observations of Multiple Sources

BOOTES network telescopes routinely conduct follow-up observations for EP-detected transients, providing detailed optical monitoring. Figure 5 shows selected sources observed across multiple epochs, demonstrating the BOOTES network’s capability to track the temporal evolution of transients.

Figure 5. Some of the EP transients that were followed up on by the BOOTES network. The sources are arranged from left to right, top to bottom: EP240315a, EP240404a, EP240413a, EP240414a, EP240416a, EP240420a, EP240426a, and EP240506a. The green circles in the image denote sources detected by the telescope’s automated source extraction algorithm. However, not all of these correspond to confirmed optical counterparts of the EP X-ray transient sources; some may be unrelated background objects or noise.

Optical light curves can be also provided automatically. As an example, the optical light curves of EP250110a, a flare star observed on 10 January 2025, using BOOTES-6 and BOOTES-7, are shown in Figure 6. These observations highlight significant brightness and color variations, with the z-band consistently showing brighter magnitudes compared to the r-band, suggesting significant spectral evolution, as seen in most active star flares [16].

Figure 6. Filter-specific light curves of RX J0429.3-3124 obtained from BOOTES-6 (B6) and BOOTES-7 (B7) observations. Different filters are represented by distinct colors and symbols as indicated in the legend. Open symbols denote observations under suboptimal atmospheric conditions.

By focusing on the optical data and emphasizing response times, this section underscores BOOTES’s role in providing rapid and high-quality follow-up observations that complement EP’s X-ray detections.

3. Overview of EP X-Ray Transients During the First Year

The spatial distribution of all EP transients detected during the first year of operation (from 19 February 2024 to 26 February 2025) is presented in Figure 7. A total of 128 transients were identified, with Fast X-ray Transients (FXTs) being the most numerous events (amounting to 52), followed by Gamma-Ray Bursts (GRBs) with 30 events, Stellar Flares with 28 events (bearing in mind that a very significant number remain unreported), Known Sources/Unclassified (14 events), and Optical Transients (4 events). The distribution exhibits a relatively isotropic pattern across the sky, with sources detected at all declinations. However, a slight deficit is observed near the Galactic plane, likely due to absorption effects and source confusion in these densely populated regions. This highlights the challenges of detecting transients in crowded fields, despite EP/WXT’s wide field of view and sensitivity.

Figure 7. All-sky distribution of EP transients detected during the first year of operations, displayed in dual Aitoff projections with different coordinate centering. (a) Galactic distribution centered at RA = 0 h (vernal equinox) and (b) RA = 12 h (autumnal Equinox), both in J2000 equatorial coordinates. Source classes are differentiated by distinct markers: Gamma-Ray Bursts (blue circles), Fast X-ray Transients (green squares), Optical Transients (orange triangles), Stellar Flares (red crosses), and Known Sources/Unclassified (gray dots). The dashed black line traces the Galactic plane, while the blue shaded region demarcates the EP/WXT’s instantaneous 60° × 60° field of view. This dual projection demonstrates complete celestial coverage and reveals longitudinal variations in transient distributions.

3.1. Source Classification

To systematically categorize the X-ray transients detected by EP, we classify each source into a primary category based on its dominant characteristics while noting any secondary classifications where applicable. The classification criteria are as follows:

• Gamma-Ray Bursts (GRBs):

  −

  Identified based on high-energy X-ray/gamma-ray emissions.

  −

  Typically exhibit short (<2 s) or long (≳2 s) durations with rapid flux variability [17].

  −

  If associated with a known GRB event (e.g., detected by Fermi-GBM or Swift), they are classified as GRBs.

  −

  Sources with possible GRB-like properties but lacking definitive confirmation are marked as “Likely GRB”.

• Fast X-ray Transients (FXTs):

  −

  Short-lived (typical time scale range of seconds to kiloseconds) X-ray flares without clear GRB signatures [18].

  −

  Exhibit sudden onset and rapid decay in flux.

  −

  May lack a known gamma-ray counterpart but show variability consistent with X-ray transients.

  −

  If an FXT also has multi-wavelength detections, it is marked with additional secondary classifications.

• Optical Transients (OTs):

  −

  Transients with detected optical counterparts, either from follow-up observations or archival surveys.

  −

  Includes events such as Fast Blue Optical Transients (FBOTs) and optical afterglow candidates of GRBs.

  −

  If an optical transient is associated with a confirmed astrophysical event (e.g., a supernova), this is noted in the classification.

• Stellar Flares (M-dwarf Flares):

  −

  X-ray events associated with active low-mass stars (e.g., M-dwarfs).

  −

  Identified based on position coincidence with known stellar objects (e.g., Gaia DR3 sources).

  −

  Typically exhibit high-energy flaring activity over timescales of seconds to minutes.

• Known Sources/Unclassified:

  −

  Transients that do not fit neatly into any of the above categories.

  −

  May include weak X-ray sources, events with insufficient data for robust classification, or candidates for future multi-wavelength follow-up.

  −

  X-ray activity from cataloged astrophysical objects such as cataclysmic variables (CVs), high-mass X-ray binaries (HMXBs) or active galactic nuclei (AGNs).

Each transient is assigned to a single primary category based on the dominant observed characteristics, with secondary classifications given in the “Notes” column, where applicable. This approach ensures that sources are not double-counted in statistical analyses while preserving additional classification context.

Rationale for Using First Observation Data: The data presented in the “X-ray properties” column of Table 3 are based solely on the initial observations made by the EP/FXT. This decision is motivated by the need for a uniform and consistent basis for classifying and comparing X-ray transients. The initial observation allows for determining the fundamental physical parameters (e.g., duration, peak flux, photon index) at the time of detection, which are crucial for establishing the primary characteristics of each event. Although follow-up observations provide valuable insights into the temporal evolution and multi-wavelength behavior of the transients, incorporating these later data in the same column could lead to confusion by mixing the initial detection with subsequent changes. Instead, any supplementary information from follow-up observations is discussed in the following section (or in the accompanying notes).

Table 3. Classification of EP sources based on their nature and multi-wavelength observations.

Name	RA (deg)	Dec (deg)	X-Ray Properties	Notes
Gamma-Ray Bursts (GRBs)
EPW20240219aa	80.016	25.541	Fast rise to $F_{\mathrm{peak}}\sim 5\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4.0 keV) in ∼10 s, decaying to background ($4\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$) in ∼200 s. Spectrum: absorbed power-law with $\Gamma =2.0_{-0.8}^{+0.9}$, $N_H=8.6_{-0.4}^{+0.5}\times {10}^{21}{\mathrm{cm}}^{-2}$. $F_{\mathrm{unabs}}=6.9_{-2.1}^{+5.6}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	A weak, untriggered gamma-ray counterpart detected
EP240315a	141.644	−9.547	Duration: ∼1600 s, $F_{\mathrm{peak}}$: $\sim 3\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=(1.5_{-0.9}^{+1.0})\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma$: $1.7_{-0.4}^{+0.4}$, $F_{\mathrm{unabs}}$: $(5.3_{-0.7}^{+1.0})\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Mainly classified as GRBs, with secondary characteristics of FXTs and OTs (z = 4.859)
LXT240402A	245.451	25.763	$N_H=4.3\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.7_{-0.1}^{+0.1}$, F (0.5–10 keV band): $7.8_{-0.8}^{+0.8}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Long GRB, associated with GRB 240402B, detected in 0.5–4 keV soft X-ray band, with FXT and OT secondary characteristics
EP240617a	285.030	−22.561	$F_{\mathrm{peak},\mathrm{unabs}}$: $\sim (1.4\pm 0.1)\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.1\pm 0.1$, $N_H=1.7\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}$: $(3.5\pm 0.3)\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	X-ray-rich GRB, weak gamma-ray counterpart in Fermi/GBM data, likely GRB secondary classification
GRB240627B	215.25	48.52	1st Exposure: 586 s, Upper limit: $4.43\times {10}^{-11}$ erg s−1 cm−2; 2nd Exposure: 1233 s, Upper limit: $2.90\times {10}^{-11}$ erg s−1 cm−2	GRBs detected by SVOM: X-ray Upper Limits from EP-WXT
GRB240629A	314.4	−35.7	1st Exposure: 6429 s, Upper limit: $1.18\times {10}^{-11}$ erg s−1 cm−2; 2nd Exposure: 54,140 s, Upper limit: $3.93\times {10}^{-12}$ erg s−1 cm−2	GRBs detected by SVOM: X-ray Upper Limits from EP-WXT
GRB240713A	352.59	1.88	A total of 13.3 h after the detection of SVOM/ECLAIRs, the exposure time is about 6.8 ks; 10 X-ray sources were found within the SVOM/ECLAIRs localization error box	X-ray follow-up observation with EP-FXT
EP240802a	287.8070	−2.3125	Dur. > 500 s, lightcurve from WXT shows three sequentially weakened peaks, $N_H=2.5_{-1.8}^{+2.0}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =0.{94}_{-0.56}^{+0.59}$, and $F_{\mathrm{unabs},\mathrm{average}}=1.7_{-0.3}^{+0.4}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. For the average FXT spectrum in the 0.5–10 keV band, $N_H=4.8_{-1.2}^{+1.4}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =1.{89}_{-0.31}^{+0.33}$, $F_{\mathrm{unabs},\mathrm{average}}=1.3_{-0.1}^{+0.2}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with long GRB 240802A
EP240804a	337.644	−39.121	For the WXT observed transient: Dur. > 100 s, $N_H=1.1_{+37.0}^{-1.0}\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =0.7_{+1.2}^{-0.4}$, $F_{\mathrm{unabs},\mathrm{average}}=6.1_{+2.6}^{-1.6}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV) For the FXT: The light curve shows significant variability. For the 0.5–10 keV spectrum, $N_H=2.8_{-2.7}^{+2.7}\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.6_{-0.1}^{+0.1}$, $F_{\mathrm{unabs},\mathrm{average}}=2.2_{-0.1}^{+0.1}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with GRB 240804B; optical candidate with large deviation detected
EP240807a	300.970	−68.777	Dur. ∼ 70 s, $F_{\mathrm{peak}}$: $\sim 1\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =0.9_{-0.8}^{+1.7}$, $N_H=1.1_{-1.1}^{+1.6}\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}$: $1.7_{-0.6}^{+0.7}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with GRB 240807A; X-ray afterglow confirmed by EP-FXT
GRB240821A	354.23	−10.18	source #1 (RA = 354.2701 deg, DEC = −10.1911 deg): 1st epoch: TGRB-Tstart = 8.8 h, Exposure = 5.0 ks, Estimated Flux = $(1.1\pm 0.2)\times {10}^{-13}$ erg s−1 cm−2; 2nd epoch: TGRB-Tstart = 15.2 h, Exposure = 8.0 ks, Estimated Flux = $(5.9\pm 1.3)\times {10}^{-14}$ erg s−1 cm−2; 3rd epoch: TGRB-Tstart = 111.4 h, Exposure = 8.4 ks, Estimated Flux < $1.5\times {10}^{-14}$ erg s−1 cm−2 source #2 (RA = 354.1516 deg, DEC = −10.0504 deg): 1st epoch: TGRB-Tstart = 8.8 h, Exposure = 5.0 ks, Estimated Flux = $(6.0\pm 1.3)\times {10}^{-14}$ erg s−1 cm−2; 2nd epoch: TGRB-Tstart = 15.2 h, Exposure = 8.0 ks, Estimated Flux = $(3.5\pm 1.0)\times {10}^{-14}$ erg s−1 cm−2; 3rd epoch: TGRB-Tstart = 111.4 h, Exposure = 8.4 ks, Estimated Flux < $3.4\times {10}^{-14}$ erg s−1 cm−2	Detected as a short-duration GRB by multiple instruments, with X-ray afterglow
EP240913a	16.681	16.750	At ∼T0 + 180 s, the light-curve has a fast pulse (Dur. ∼50 s) followed by weak emission up to 1100 s. $F_{\mathrm{peak}}$: $\sim 2\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =0.5_{-0.6}^{+0.6}$, $N_H=5.1\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}$: $1.1_{-0.4}^{+0.5}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Short gamma-ray burst, consistent in time and space with X-ray transient
EP240919a	334.2797	−9.7362	Dur. > 400 s, $N_H=5.4\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.3_{-0.3}^{+0.3}$, $F_{\mathrm{absorbed},\mathrm{average}}=7.0_{-1.5}^{+1.8}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV)	Associated with long GRB 240919A; radio counterpart candidate detected at 9 GHz
EP240930a	319.899	41.303	$\Gamma =0.{79}_{-0.25}^{+0.24}$, $N_H=3.29\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}$: $3.8_{-0.5}^{+0.5}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Consistent with long GRB 240930B in time and space, X-ray afterglow characteristics support GRB classification, also has FXT characteristic in initial stage
GRB241001A	20.55276	−43.47506	The source faded by an order of magnitude to $F_X=(5.1\pm 1.2)\times {10}^{-14}$ erg cm−2 s−1 in the 0.3–10 keV band. Confirmed: Swift/XRT source #2 is the afterglow of GRB 241001A	The optical counterpart was detected, qualifies as an X-Ray Flash (XRF), z = 0.573
GRB241018A	67.9992	43.0200	$N_H=9.5_{-5.7}^{+6.9}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =2.5_{-1.1}^{+1.2}$, Observed flux (0.5–10.0 keV): $1.8_{-0.7}^{+1.6}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Detected by multiple gamma-ray detectors, X-ray afterglow consistent with GRB characteristics
EP241025a	333.6408	83.5772	Trigger flux (0.5–4 keV, assumed $\Gamma =2$ absorbed power-law): $\sim 2\times {10}^{-10}$ erg s−1 cm−2, Source flux: $\sim 5\times {10}^{-11}$ erg s−1 cm−2	Long GRB, the optical counterpart was detected, z = 4.20
EP241030a	343.013	80.449	$\Gamma =2.5_{-0.7}^{+0.8}$, $N_H=1.8\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}$: $7.5_{-2.4}^{+3.0}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	GRB 241030A X-ray Afterglow
EP241104a	32.574	31.555	Dur. $\sim 400s$, $F_{\mathrm{peak}}$: $\sim 5.0\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), $\Gamma =1.3_{-0.7}^{+0.8}$, $N_H=7.8\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}$: $2.0_{-1.1}^{+1.0}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with known GRB 241104A
GRB241105A	61.9	−46.7	For the two observations, the first one has an exposure time of 2894 s, $T_{mid}-T_0$ of 22.0 h, and a flux in the 0.5–10 keV band of $(1.51\pm 0.31)\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$; the second one has an exposure time of 7966 s, $T_{mid}-T_0$ of 38.0 h, and a flux in the 0.5–10 keV band of $(3.79\pm 0.50)\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Known GRB event, multi-band observations support short-burst with extended radiation characteristics
EP241113b	110.233	46.800	$\Gamma =1.5_{-0.7}^{+0.7}$, $N_H=2.7\times {10}^{21}{\mathrm{cm}}^{-2}$ (with an uncertainty of $\pm 1.8\times {10}^{21}{\mathrm{cm}}^{-2}$), $F_{\mathrm{unabs}}$: $1.5_{-0.4}^{+0.4}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, Dur. of lightcurve from WXT = 100 s	Associated with known GRB event, multi-band observations support the classification
EP241115a	19.416	−17.954	$\Gamma =1.{50}_{-0.38}^{+0.38}$, $N_H=1.6\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs},0.3–10\mathrm{keV}}$: $2.1_{-0.5}^{+0.9}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with GRB 241115D
EP241213a	116.182	35.271	$\Gamma =2.2_{-1.4}^{+1.4}$, $N_H=5.9\times {10}^{21}{\mathrm{cm}}^{-2}$ (with an uncertainty of $\pm 4.8\times {10}^{21}{\mathrm{cm}}^{-2}$), $F_{\mathrm{unabs}}$: $5.2\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with long GRB 241213A
EP241217b	84.167	−25.281	WXT: - Light curve: 2 pulses. 1st from 10–620 s (2 short pulses at 150 s and 260 s, slewing 53–134 s), 2nd from 1000–1500 s. - Spectrum (134–2000 s after GRB trigger): Absorbed power-law, $N_{H,MW}=1.79\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $z=1.195$, $N_{H,int}=1.{42}_{-0.46}^{+0.51}\times {10}^{22}{\mathrm{cm}}^{-2}$, $\Gamma =1.{57}_{-0.21}^{+0.22}$, $F_{\mathrm{unabs},0.5–4\mathrm{keV}}=(1.19\pm 0.10)\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ FXT: - Spectrum (134–7800 s after GRB trigger, annular region): Same model as WXT. $N_{H,int}=0.85\pm 0.06\times {10}^{22}{\mathrm{cm}}^{-2}$, $\Gamma =1.58\pm 0.04$, $F_{\mathrm{unabs},0.5–10\mathrm{keV}}=1.1\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with GRB 241217A, z = 1.879
GRB241229A	192.893	31.857	EPF_J125139.4 + 315,311: R.A. = 192.9133 deg, DEC = 31.8867 deg, Sep. = 2.06 arcmin, F = $6.82\times {10}^{-14}$ erg s−1 cm−2 EPF_J125129.3 + 314,453: R.A. = 192.8715 deg, DEC = 31.7484 deg, Sep. = 6.61 arcmin, F = $7.73\times {10}^{-13}$ erg s−1 cm−2 EPF_J125101.6 + 315,007: R.A. = 192.7572 deg, DEC = 31.8356 deg, Sep. = 7.04 arcmin, F = $9.25\times {10}^{-14}$ erg s−1 cm−2	Long GRB, EP-FXT detected afterglow candidates
EP250109a	88.806	−12.500	WXT (EP250109a, trigger at 2025-01-09T06:17:58 UTC): - Peak: ∼60 s post-trigger, $F_{\mathrm{peak},0.5–4\mathrm{keV}}\approx 2.5\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ - Decay: To background within 200 s post-trigger - Spectrum: Absorbed power law, $\Gamma =2.9\pm 1.0$, $N_{H,Gal}=3.04\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $z=0$, $N_{H,int}=5.0_{-0.3}^{+0.4}\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs},0.5–4\mathrm{keV}}=2.5_{-1.2}^{+4.6}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ FXT (Obs. start: 2025-01-09T08:06:40 UTC, ∼1.8 h post-trigger, $t_{exp}\approx 4.2$ ks): - Spectrum: Absorbed power-law, $\Gamma =1.9_{-0.7}^{+1.9}$, $N_{H,Gal}=3.04\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $z=0$, $N_{H,int}\approx 3\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs},0.5–4\mathrm{keV}}=4.9_{-1.2}^{+2.0}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with GRB 250109A, multi-band observations support the classification
GRB250127A	169.6284	3.3508	$\Gamma =1.{79}_{-0.92}^{+0.92}$, $N_{H,Gal}=4.52\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs},0.5–10\mathrm{keV}}$: $1.{30}_{-0.68}^{+1.44}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Long GRB event
EP250205a	113.522	32.363	WXT (0.5–4.0 keV): - Absorbed power-law, $N_{H,Gal}=4.4\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $z=3.55$ - $N_{H,int}=6.5_{-6.5}^{+9.8}\times {10}^{22}{\mathrm{cm}}^{-2}$, $\Gamma =2.5_{-1.2}^{+1.7}$, $F_{\mathrm{unabs},0.5–4\mathrm{keV}}=4.2_{-1.1}^{+1.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ EP-FXT (average 0.5–10 keV): - Absorbed power-law, $N_{H,Gal}=4.4\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed) - $\Gamma =2.{82}_{-0.04}^{+0.06}$, $F_{\mathrm{unabs},0.5–10\mathrm{keV}}=3.{65}_{-0.09}^{+0.07}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with GRB 250205A, optical counterpart was detected
EP250215a	156.3430	−27.7040	Duration = —, Peak flux = —	Associated with long GRB 250215A, optical counterpart was detected, z = 4.61
EP250226a	224.273	20.973	WXT detection: Dur. $=22$ s, $F_{\mathrm{peak},0.5–4\mathrm{keV}}=9.8\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (trigger at 2025-02-26T06:34:54 UTC). FXT follow-up: First epoch (44 min post-trigger): $\Gamma =2.{07}_{-0.06}^{+0.06}$, $N_{H,Gal}=3.7\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs},0.5–10\mathrm{keV}}=2.{89}_{-0.08}^{+0.08}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ at R.A. = 224.2641°, Dec. = 20.9754° (10 arcsec error). Second epoch (11.9 h post-trigger): $F_{\mathrm{unabs},0.5–10\mathrm{keV}}=1.{83}_{-0.18}^{+0.18}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, indicating X-ray ${\mathrm{L}}_{\mathrm{jump}}\sim 16\times$ decline	Associated with GRB 250226A, optical counterpart detected, z = 3.315
Stellar Flares (M-dwarf flares)
EP trigger ID 01708913080	336.13	−58.429	Spectrum Model: Two apec components, $T_1=0.{89}_{-0.07}^{+0.05}$ keV, $T_2=2.9\pm 0.3$ keV, $F_{\mathrm{FXT},0.5–10\mathrm{keV}}=3.0\pm 0.1\times {10}^{-11}$ erg s−1 cm−2 (2 orders of magnitude higher than eROSITA flux) If associated with M star, $L_{\mathrm{peak}}=7.6\times {10}^{29}\mathrm{erg}{\mathrm{s}}^{-1}$	Associated with M-dwarf UPM J2224-5826, X-ray flux significantly higher than eROSITA historical value
EP trigger ID 01708981728	336.513	−15.302	Spectrum Model: Two absorbed apec components, $T_1=0.93\pm 0.03$ keV, $T_2=4.1\pm 0.2$ keV, $N_H=9.0_{-0.6}^{+0.7}\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs},0.5–10\mathrm{keV}}=3.6\pm 0.3\times {10}^{-10}$ erg s−1 cm−2 If associated with high-proper-motion star, $L_{\mathrm{peak},0.5–10\mathrm{keV}}=4.0\times {10}^{31}$ erg s−1	Associated with high-proper-motion star LP 820-19, optical observation confirms significant brightness enhancement during flare
EP trigger ID 01709018832	2.562	−2.665	Spectrum Model: Two absorbed apec components, $T_1=1.{03}_{-0.08}^{+0.08}$ keV, $T_2=4.{49}_{-0.76}^{+1.10}$ keV, $N_H=0$ (fixed) $F_{0.5–10\mathrm{keV}}=6.{51}_{-0.51}^{+0.55}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ If source associated with star, $L_{\mathrm{peak}}=4.1\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	Associated with M-dwarf Gaia DR3 2445442335531658752, optical observation shows significant brightness change during flare
EP trigger ID 01709059262	278.807	24.588	The position of the FXT source is associated with the star 2MASS J18351416 + 2,435,115	Spectrum: Red continuum + strong Balmer, Ca II H&K, TiO emission lines, consistent with dMe star spectrum
EP trigger ID 01709061302	350.5437	−3.0283	The FXT source is associated with a K-type star, PM J23221-0301, at a distance of about 46 pc and located about 8 arcsec away from the FXT position	—
EP trigger ID 01709064214	352.558	−2.614	n M-type, high proper motion star 2MASS J23301129-0237227/2RXS J233013.0-023738, is at a distance of about 46 pc and located about 5.1 arcsec away from the position detected by FXT	The X-ray transient was also detected in the optical and confirm it originated from a flare star
EP trigger ID 01709065118	344.5674	−11.0724	The FXT source is associated with an M-type star, 1RXS J225817.2-110434, at a distance of about 32 pc and located about 5 arcsec away from the FXT position	Spectra: Red continuum + strong H Balmer, Ca II H&K, TiO emission lines, consistent with dMe star spectrum. Photometry: Trigger event associated with stellar flare
EP241109a	18.3599	0.0184	In GAIA DR3, a close star ($T_{\mathrm{eff}}\approx 3200$ K, $d\approx 71.83$ pc) lies within EP-FXT error circle of EP241109a	GAIA DR3 2534635509050352256: Brightness decreased by 0.8 mag (clear filter) in 40 min, confirming EP241109a as a stellar flare. Based on photometry and spectroscopy, EP241109a event is associated with this stellar flare
EP trigger ID 01709120856	4.023	−16.604	$F_{\mathrm{peak}}\approx 8\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $L_X\approx 3\times {10}^{30}\mathrm{erg}{\mathrm{s}}^{-1}$ (typical for M-type dwarf)	—
EP trigger ID 01709122294	64.628	28.458	Spectrum Model: Absorbed apec, $T=3_{-1}^{+5}$ keV $F_{\mathrm{unabs},0.5–4\mathrm{keV}}=3.7_{-1.1}^{+1.3}\times {10}^{-11}$ erg s−1 cm−2 If the transient is associated with V410 Tau, $L_{0.5–4\mathrm{keV}}\approx 7.3\times {10}^{31}$ erg −1	Flare decay in observations: - In u and v bands: magnitudes decayed  0.24 and 0.11 in  7 h. - In g and r bands: no significant variations
EP trigger ID 01709128921	63.363	−1.648	Associated with a double or multiple star RX J0413.4-0139, $F_{\mathrm{peak}}\approx 2.0\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 1.7\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709128948	79.405	−7.557	Associated with a young stellar object candidate ATO J079.4052-07.5576, $F_{0.5–10.0\mathrm{keV}}\approx (1.05\pm 0.02)\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx (1.74\pm 0.03)\times {10}^{33}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709129023	151.839	69.35	Associated with an eruptive variable UCAC4 797-019583, $F_{\mathrm{peak}}\approx 1.8\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 6\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709129287	88.836	−14.381	Associated with a high proper motion star TYC 5360-423-1, $F_{0.5–10.0\mathrm{keV}}\approx 2\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 5\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709129925	90.609	−16.579	Associated with a high proper motion star 1RXS J060224.9-163451, $F_{\mathrm{peak}}\approx 1\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 2\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709130111	67.339	−31.395	Associated with a low-mass star, RX J0429.3-3124, $F_{\mathrm{peak}}\approx 1.6\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 5.5\times {10}^{30}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709131085	72.216	10.03	Associated with a high proper motion star RX J0448.7 + 1003, $F_{\mathrm{peak}}\approx 2.0\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $L_X\approx 7.1\times {10}^{30}\mathrm{erg}{\mathrm{s}}^{-1}$	Photometry: - At 26.7 min, $B\approx 13.2$ mag. - Peaked at 43.6 min with $B\approx 12.9$ mag. - At 187 min, $B\approx 13.6$ mag. Conclusion: EP-WXT trigger event is associated with the stellar flare
EP trigger ID 01709131196	139.021	1.89	Associated with an M-type star RX J0916.1 + 0153, $L_{0.5–10\mathrm{keV}}^{\mathrm{preliminary}}\approx 5.4\times {10}^{29}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709131290	88.148	−53.067	Associated with a star UCAC4 185-006985, $F_{\mathrm{peak}}\approx 1.9\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 5.5\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709131332	184.462	−36.741	Associated with a high proper motion star UPM J1217-3644, $F_{\mathrm{peak}}\approx 1.2\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $L_X\approx 1.2\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
The EP trigger 01709131347	158.298	34.176	Associated with a spectroscopic binary G 118-68, $F_{\mathrm{peak}}\approx 1.0\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 2.5\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP250207a	356.902	27.027	Associated with low-mass star 2MASS J23473680 + 2,702,068, 0.5–4 keV single-apec fit - Spectrum fit: 0.5–4 keV spectrum fitted with a single apec model, $T=3.1_{-1.2}^{+5.9}$ keV, no significant absorption. - Flux: $F_{0.5–4\mathrm{keV}}=2.9_{-0.7}^{+0.9}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ 0.3–10 keV two-apec fit - Spectrum fit: 0.3–10 keV spectrum fitted with two apec components, $T_1=0.{75}_{-0.3}^{+0.2}$ keV, $T_2=2.6_{-0.6}^{+1.3}$ keV, no significant absorption. - Flux and luminosity: $F_{0.3-10\mathrm{keV}}=9.2_{-1.0}^{+1.1}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $L_X\approx 5\times {10}^{29}\mathrm{erg}{\mathrm{s}}^{-1}$	This high-proper-motion M9 dwarf brightened from $r=19.8\pm 0.1$ (Pan-STARRS) to $r=16.9\pm 0.1$. Gaia DR3 shows a proper motion of $315.33\pm 0.21$ mas/yr and parallax of $46.76\pm 0.16$ mas, suggesting it is a nearby star having a +3-mag flare
EP J0433.6+3255	68.4	32.917	Dur. $>2000$ s. The source is $\sim 30$ arcsec from an ROSAT X-ray source (1RXS J043335.1 + 325,432), which is spatially consistent with a nearby M-type star (Gaia DR3 172042272322881792; Assoc.: M-type star). The separation between the star and 1RXS J043335.1 + 325,432 is 11 arcsec. The outburst may be associated with both the M-type star (Assoc.: M-type star) and the X-ray source (Assoc.: X-ray source). If confirmed, the X-ray $F_{\mathrm{peak}}$ would show a ∼100-fold increase compared to the ROSAT $F_{\mathrm{peak}}$ ($2.2\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$). The WXT spectrum is best fitted by an absorbed power-law with $\Gamma =2.5_{-1.7}^{+1.8}$ and $N_H=2.3\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed). The corresponding $F_{\mathrm{unabs}}$ is $3.0_{-1.3}^{+1.7}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. If associated with Gaia DR3 172042272322881792, the 0.5–4 keV luminosity $L_{\mathrm{X}}\approx 6.4\times {10}^{30}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP J0452.7-0541	73.176	−5.687	Source position matches 1eRASS J045241.6-054101 with $F_{\mathrm{peak}}$ $=3.0\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.2–2.3 keV). Associated with Gaia DR3 3188422199717067648 (separation 1.4 arcsec; Assoc.: star). WXT spectrum: abs apec model with $T=2.8_{-1.0}^{+3.7}$ keV, $N_H=3.8\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=4.3_{-1.1}^{+1.4}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (∼100× brighter than eROSITA). If associated, $L_{\mathrm{X}}\approx 3.9\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$ (0.5–4 keV)	—
RX J0218.7+3854	34.6990	38.9136	FXT source spatially matches Gaia DR3 331926892386271872 (offset 3 arcsec; Assoc.: Gaia object). Spectrum (0.5–10 keV): absorbed power-law with $\Gamma =2.6_{-0.2}^{+0.2}$, $N_H=5.47\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=4.9_{-0.4}^{+0.5}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, consistent with historical ROSAT flux. Spatial correlation with EP241206a suggests the WXT detection may represent an X-ray outburst from RX J0218.7 + 3854	—
EP241212a	153.817	60.068	Faint X-ray source 1WGA J1015.3 + 6004/Gaia DR3 1048515045825830144 (R.A. = 153.83607, Dec. = +60.07485) at $d\approx 107$ pc, offset 42 arcsec from WXT position. No significant variability. WXT spectrum: absorbed power-law with $\Gamma =2.7_{-1.0}^{+1.0}$, $N_H=3.8_{-2.7}^{+2.7}\times {10}^{21}{\mathrm{cm}}^{-2}$. Absorbed 0.5–4 keV flux: $1.9_{-0.2}^{+0.2}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	—
EP trigger ID 01709131775	80.748	−8.833	Associated with a T Tauri star RX J0523.0-0850, $F_{\mathrm{peak}}\approx 8.0\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 2.2\times {10}^{32}\mathrm{erg}{\mathrm{s}}^{-1}$	—
EP trigger ID 01709131882	170.244	−38.768	Associated with a BY Dra Variable V1217 Cen, $F_{\mathrm{peak}}\approx 1.0\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, corresponding to $L_X\approx 5.1\times {10}^{31}\mathrm{erg}{\mathrm{s}}^{-1}$	—
Fast X-ray Transients
EP240305a	122.903	−54.657	Light curve shows double-peak profile. First flare: rise to $F_{\mathrm{peak}}\sim 5\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4.0 keV) in ∼100 s, decay to background ($\sim 1\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$) in ∼50 s. Second flare: rise to $F_{\mathrm{peak}}\sim 2.5\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ in ∼50 s, decay to background in ∼200 s. Averaged spectrum: absorbed power-law with $\Gamma =1.6_{-0.5}^{+0.5}$, $N_H=3.4_{-1.7}^{+1.8}\times {10}^{21}{\mathrm{cm}}^{-2}$. $F_{\mathrm{unabs}}=8.3_{-1.4}^{+2.0}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Maybe a late A or early F spectral-type star; radio counterpart detected
EP240331a	169.414	−20.042	Light curve: symmetric profile, Dur. ∼ 100 s. Spectrum: absorbed power-law with $\Gamma =0.{74}_{-0.30}^{+0.31}$, $N_H=3.44\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=1.8_{-0.3}^{+0.3}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV)	—
EP240408a	158.840	−35.749	Dur. ∼ 10 s. $F_{\mathrm{peak}}\sim 1.4\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4.0 keV). Spectrum: absorbed power-law with $\Gamma =1.1_{-0.7}^{+0.8}$, $N_H=6.23\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=4.0_{-1.3}^{+1.3}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	Optical/NIR counterpart detected
EP240413a	228.794	−18.800	Dur. = 200 s, $F_{\mathrm{peak}}=7\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.6_{-0.2}^{+0.1}$, $N_H=1.12\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=1.1_{-0.1}^{+0.1}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	If possible detection of the X-ray emission is true, EP240413a has faded by about 3 orders of magnitude in X-ray flux in about 14 h
EP240416a	203.150	−13.612	Dur. ≥ 200 s, $F_{\mathrm{peak}}=1.3\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=4.0\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.5_{-0.6}^{+0.6}$, $F_{\mathrm{unabs}}=5.0_{-1.6}^{+2.6}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical counterpart candidate detected
EP240417a	177.442	−15.438	Dur. ≥ 1500 s, $F_{\mathrm{peak}}=3\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.{15}_{-0.26}^{+0.27}$, $N_H=0$, $F_{\mathrm{unabs}}=9.8_{-0.8}^{+0.8}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No other band counterparts
EP240420a	228.713	14.796	Dur. > 100 s, $F_{\mathrm{peak}}=1\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Short-time X-ray flare; X-ray flux decays by 3 orders of magnitude in 2 h; optical counterpart detected
EP240426b	173.787	−40.741	Dur. = 300 s, $F_{\mathrm{peak}}=9.5\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.8_{-0.3}^{+0.3}$, $N_H=8.08\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=3.6_{-0.6}^{+0.6}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No multi-band counterpart; 40-degree deviation from S240422ed
EP240506a	213.978	−16.715	Dur. = 50 s, $F_{\mathrm{peak}}=1\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.0_{-0.5}^{+0.5}$, $N_H=9.0\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=1.1_{-0.2}^{+0.3}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No optical counterpart detected; possible background radio source
EP240518a	216.955	−49.565	Dur. > 1000 s, average $F=8\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV)	Possible stellar activity
EP240618a	281.648	23.833	Dur. ≈ 100 s, $F_{\mathrm{unabs},\mathrm{peak}}=1.5\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.2_{-0.4}^{+0.4}$, $N_H=1.98\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs},\mathrm{average}}=2.9_{-0.6}^{+0.7}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical candidate detected
EP240625a	310.760	−15.966	Dur. ≈ 300 s, $F_{\mathrm{unabs},\mathrm{peak}}=1.3\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.8_{-0.3}^{+0.3}$, $N_H=3.85\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs},\mathrm{average}}=2.9_{-0.5}^{+0.7}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	X-ray source decays slowly; optical candidate with low SNR detected
EP240626a	263.023	−13.051	Dur. ≈ 160 s, $F_{\mathrm{unabs},\mathrm{peak}}=6\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =0.{95}_{-0.54}^{+0.54}$, $N_H=1.8\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs},\mathrm{average}}=1.{70}_{-0.50}^{+0.73}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Weak follow-up X-ray source detected; no optical counterpart
EP240702a	328.203	−38.980	Dur. ≈ 50 s, $F_{\mathrm{peak}}=1.2\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.1_{-0.2}^{+0.2}$, $N_H=2.0\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs},\mathrm{average}}=5.4_{-1.2}^{+1.5}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No optical or radio counterpart; no matching known X-ray source
EP240703a	273.803	−9.681	Dur. ≈ 300 s, $F_{\mathrm{peak}}=5\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (absorbed), $N_H=1.5_{-0.6}^{+0.7}\times {10}^{22}{\mathrm{cm}}^{-2}$, $\Gamma =2.0_{-0.9}^{+1.0}$, $F_{\mathrm{unabs},\mathrm{average}}=5.9_{-2.6}^{+8.6}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$; When $N_H=4.5\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =0.4_{-0.3}^{+0.3}$, $F_{\mathrm{unabs},\mathrm{average}}=2.5_{-0.3}^{+0.4}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical candidate detected but not independently confirmed; no matching known X-ray source
EP240703b	279.539	−57.401	Dur. ≈ 600 s, $F_{\mathrm{peak}}=3\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (absorbed), $N_H=1.4_{-1.2}^{+1.3}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =1.5_{-0.5}^{+0.6}$, $F_{\mathrm{unabs},\mathrm{average}}=7.5_{-1.8}^{+1.3}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$; When $N_H=6.8\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.2_{-0.2}^{+0.2}$, $F_{\mathrm{unabs},\mathrm{average}}=7.1_{-1.0}^{+1.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No multi-band counterpart
EP240703c	289.264	−30.325	Dur. > 1000 s, with multipeak lightcurve structure, $N_H=8\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.3_{-0.5}^{+0.5}$, $F_{\mathrm{unabs}}=2.5_{-0.8}^{+0.8}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No clear multi-band counterpart; no matching known X-ray source
EP240708a	345.963	−22.840	Dur. ≈ 1300 s, $F_{\mathrm{peak}}=1.1\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=2.0\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.{57}_{-0.54}^{+0.63}$, $F_{\mathrm{unabs},\mathrm{average}}=7.7_{-2.6}^{+3.4}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Weak follow-up X-ray source detected
EP240801a	345.140	32.610	Dur. > 80 s, lightcurve from WXT shows rapid brightening profile, $N_H=3.1_{-3.1}^{+3.1}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =1.9_{-0.9}^{+0.9}$, $F_{\mathrm{unabs},\mathrm{average}}=4.8_{-3.1}^{+3.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV)	X-ray afterglow detected; optical candidate detected in the error circle, z = 1.673
EP240806a	11.491	5.091	Dur. ≈ 150 s, $N_H=3.1_{+2.8}^{-2.5}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =2.6_{+1.2}^{-1.0}$, $F_{\mathrm{unabs},\mathrm{average}}=1.9_{+1.8}^{-0.6}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical counterpart detected, z = 2.818
EP240816b	16.013	15.398	For the WXT: Dur. > 50 s, $N_H=5.2\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.6_{-0.7}^{+0.7}$, $F_{\mathrm{unabs},\mathrm{average}}=1.3_{-0.5}^{+0.7}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV) For the average FXT spectrum in 0.5–10 keV band: $N_H=9.5_{-6.7}^{+6.9}\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.{69}_{-0.22}^{+0.23}$, $F_{\mathrm{unabs},\mathrm{average}}=4.3_{-0.5}^{+0.6}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV)	No clear optical or radio counterpart
EP240816a	292.925	−54.412	$N_H=4.2\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.1_{-0.5}^{+0.6}$, $F_{\mathrm{unabs},\mathrm{average}}=3.0_{-0.5}^{+0.5}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ For the average FXT spectrum in the 0.5–10 keV band: $N_H=4.2\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.{87}_{-0.39}^{+0.40}$, $F_{\mathrm{unabs},\mathrm{average}}=1.2_{-0.3}^{+0.5}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV)	No multi-band counterpart
EP240820a	16.221	−34.698	For the WXT observed transient: Dur. ≈ 250 s, $N_H=1.62\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.2_{+0.8}^{-0.7}$, $F_{\mathrm{unabs},\mathrm{average}}=1.2_{+0.7}^{-0.5}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV) For the FXT spectrum: Fitted with an absorbed power-law, parameters fixed to those from EP-WXT spectral fitting, $F\approx 2.0\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No multi-band counterpart
EP240904a	276.8750	−9.9426	Detected by EP/WXT at 2024-09-04T17:20:40 UTC. WXT spectrum (0.5–4 keV): absorbed power-law with $\Gamma =0.6_{-1.3}^{+1.1}$, $N_H=1.32\times {10}^{22}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=4.2_{-1.6}^{+1.8}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. EP/FXT follow-up (5.9 ks exposure) localized source at R.A. = 276.8750°, Dec. = −9.9426° (J2000; 10 arcsec error radius). Spectrum (0.5–10 keV): $\Gamma =1.{95}_{-0.01}^{+0.01}$, $N_H=3.0_{-0.1}^{+0.1}\times {10}^{22}{\mathrm{cm}}^{-2}$. $F_{\mathrm{unabs}}=2.1_{-0.1}^{+0.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	Radio counterpart detected
EP240908a	14.0031	8.0735	For the WXT observed transient: Dur. ≈ 950 s, $F_{\mathrm{peak}}=1\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), $N_H=7\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.6_{+0.4}^{-0.5}$, $F_{\mathrm{unabs},\mathrm{average}}=7.4_{+2.4}^{-1.9}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV) For the FXT: $N_H=1.5_{+1.7}^{-1.5}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =2.1_{+0.7}^{-0.6}$, $F_{\mathrm{unabs}}\left(0.5–10.0\mathrm{keV}\right)=7.4_{+1.3}^{-2.0}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical counterpart detected
EP240918a	289.3937	46.1281	For the WXT observed transient: Dur. ≈ 170 s, $F_{\mathrm{peak}}\approx 3.2\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=9.9\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.7_{+0.7}^{-0.6}$, $F_{\mathrm{unabs},\mathrm{average}}=7.2_{+2.8}^{-1.9}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ For the EP-FXT light curve: Shows a fast decline, flux decreased to $\approx 1.0\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ within $\approx 1000$ s	No clear optical or radio counterpart
EP240918b	258.66	66.739	Dur. ≈ 200 s, $F_{\mathrm{absorbed},\mathrm{average}}=2.6_{-1.2}^{+4.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=3.2_{-3.2}^{+6.2}\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =1.5_{-1.3}^{+1.8}$	No clear optical or radio counterpart
EP240918c	281.338	−13.167	Dur. ≈ 100 s, $F_{\mathrm{peak}}\approx 5.8\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), $N_H=3.7\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =1.6_{-0.8}^{+0.8}$, $F_{\mathrm{unabs},\mathrm{average}}=1.5_{-0.2}^{+0.6}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No previously known bright X-ray sources are found within the error circle around the source position
EP241021a	28.852	5.957	$F_{\mathrm{peak}}\approx 1\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), $N_H=5\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.{48}_{+1.24}^{-1.22}$, $F_{\mathrm{unabs},\mathrm{average}}=3.3_{+4.8}^{-1.6}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical counterpart detected; redshift of host galaxy $z=0.748$; a bright source was detected at the optical transient (OT) position at a frequency of 5.5 GHz; the flux density of this source is ${400}_{-20}^{+20}\mu \mathrm{Jy}$
EP241026b	56.403	41.031	$F_{\mathrm{peak}}\approx 1.7\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), $N_H=3.38\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =2.5_{-0.8}^{+0.8}$, $F_{\mathrm{unabs},\mathrm{average}}=1.2_{+0.4}^{-0.3}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Short-time X-ray flare; optical candidate with 1.9-magnitude brightening detected; an upper limit of 1.8 for the redshift
EP241101a	37.763	22.731	For the WXT observed transient: Dur. > 100 s, $N_H=1.5\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =0.9_{-0.6}^{+0.6}$, $F_{\mathrm{unabs},\mathrm{average}}=1.2_{-0.4}^{+0.5}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV) For the FXT: During its autonomous observation within the WXT error circle, no significant source was detected. The flux upper limit is $7.1\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV)	Possible detection of some optical counterparts
EP241103a	27.7572	18.9587	For the WXT: Duration: ≈ 60 s, $N_H=6.3\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =0.8_{-0.4}^{+0.4}$, $F_{\mathrm{unabs},\mathrm{average}}=3.8_{-0.9}^{+1.1}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $F_{\mathrm{peak}}\approx 1.1\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ For FXT (in the 0.5–10 keV band): Exposure time: 2300 s, no significant light curve variation observed, $N_H$ fixed at Galactic value, $\Gamma =2.0_{-0.4}^{+0.4}$, $F_{\mathrm{average}}=6.0_{-1.4}^{+2.3}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No multi-band counterpart
EP241107a	35.0085	3.3329	The trigger flux: $\approx 1\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical and radio (the flux density is ${207}_{-7}^{+7}\mu \mathrm{Jy}$) counterpart candidates detected; z = 0.456
EP241113a	131.9964	52.3815	WXT Observations: - $\Gamma =1.3\pm 0.2$, $N_H=2.6\times {10}^{20}{\mathrm{cm}}^{-2}$ - $F_{\mathrm{avg}}$: $5.{57}_{-0.76}^{+1.26}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ FXT Observations: Exp. time: 5000 s, significant decline in light-curve, $\Gamma =2.40\pm 0.17$, $N_H$ fixed - $F_{\mathrm{avg}}$ in 0.5–10 keV: $2.5_{-0.2}^{+0.3}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	X-ray fading, no gamma-ray counterpart; tentative host redshift $z=1.53$, likely extragalactic origin
EP241119a	84.116	3.832	By WXT: $\mathrm{Dur}.\approx 200s$, $F_{\mathrm{peak}}\approx 4\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. $\Gamma =1.{27}_{-0.44}^{+0.45}$, $N_H=2.1\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=2.{43}_{-0.52}^{+0.67}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV).  9 h later by FXT, $F_{\mathrm{AG}}\approx 2\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	No multi-band association or optical candidate detected
EP241125a	48.561	37.677	$\mathrm{Dur}.>$ 150 s, $F_{\mathrm{peak}}\approx 8\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). $\Gamma =1.{90}_{-0.95}^{+1.12}$, $N_H=1.2\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}=2.{79}_{-0.86}^{+1.11}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	No multi-band association
EP241126a	33.744	11.705	$\mathrm{Dur}.>$ 60 s, $F_{\mathrm{peak}}\approx 2\times {10}^{-8}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). $\Gamma =0.9_{-0.4}^{+0.4}$, $N_H=7.4\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}=3.3_{-0.7}^{+0.9}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV).	Optical counterpart detected
EP241201a	282.596	66.081	$\mathrm{Dur}.\approx$ 230 s, $\Gamma =3.9_{+1.6}^{-1.4}$, $N_H=1.5_{+0.8}^{-0.6}\times {10}^{22}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=7.1_{+32.7}^{-4.9}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical candidate detected
EP241202b	45.302	2.441	$\mathrm{Dur}.>$ 140 s, $F_{\mathrm{peak}}=1.4\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. $\Gamma =1.{06}_{-0.41}^{+0.43}$, $N_H=9.5\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=5.4_{-1.6}^{+2.0}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Optical candidate detected
EP241206a	34.702	38.914	$\mathrm{Dur}.\approx$ 400 s. $\Gamma =1.{96}_{-0.40}^{+0.52}$, $N_H=5.47\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}=4.{92}_{-1.24}^{+1.19}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No multi-band counterpart detected
EP241208a	127.812	49.082	$\mathrm{Dur}.\approx$ 50 s (trigger ID: 01709128715). $\Gamma =1.{29}_{-0.88}^{+0.93}$, $N_H=4.20\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}=6.{57}_{-2.49}^{+4.73}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	The long soft transient also was detected by SVOM
EP241217a	46.957	30.901	$F_{\mathrm{peak}\mathrm{count}}\approx 1\mathrm{cnt}/\mathrm{s}$. In 0.5–4 keV, $\Gamma =1.{93}_{-0.59}^{+0.71}$ (absorbed power-law), $F_{\mathrm{unabs}}=(7.3\pm 2.7)\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. FXT follow-up: at 1.02 h post-trigger, $F_{0.5–10\mathrm{keV}}=(6.23\pm 0.46)\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$; at 8.18 h post-trigger, $F_{0.5–10\mathrm{keV}}=(1.35\pm 0.22)\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. Flux decay index $\alpha =0.73\pm 0.35$, consistent with Swift-XRT. Spectral fits: negligible intrinsic absorption, ${\Gamma }_1=1.76\pm 0.11$, ${\Gamma }_2=1.96\pm 0.17$.	Optical candidate detected; z = 4.59; radio counterpart (the flux densities are $20\pm 6.6\mu \mathrm{Jy}$ at $3\mathrm{GHz}$, $58\pm 4\mu \mathrm{Jy}$ at $6\mathrm{GHz}$, and $99.3\pm 4.1\mu \mathrm{Jy}$ at $10\mathrm{GHz}$)
EP241223a	74.804	7.110	$\mathrm{Dur}.\approx 80s$, $F_{\mathrm{peak}}\approx 2.4\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =2.{01}_{-0.85}^{+1.02}$, $N_H=1.22\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}=9.0_{-4.0}^{+4.0}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No optical counterpart or other multi-band association detected
EP241231b	100.064	16.171	$F_{\mathrm{abs}}$ (absorbed flux) $=1.5_{-0.5}^{+1.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=4.1\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =2.1_{-0.9}^{+1.1}$	No multi-band association or optical candidate detected
EP250101a	85.575	0.352	$\mathrm{Dur}.\approx 2500s$ is seen. $F_{\mathrm{peak}}\approx 1.7\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $\Gamma =1.5_{-1.1}^{+1.6}$, $N_H=3.3\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $F_{\mathrm{unabs}}=4.4_{-1.7}^{+2.3}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	No optical counterpart or other multi-band association detected
EP250109b	118.611	−14.651	Peak flux (0.5–4 keV) = $\sim 7\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, photon index (average 0.5–4 keV spectrum during flare) = $1.5_{-1.1}^{+1.2}$ (galactic column density fixed at $1.68\times {10}^{21}{\mathrm{cm}}^{-2}$), average unabsorbed 0.5–4 keV flux = $(3.0_{-1.2}^{+2.3})\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Distance error circle of the nearby eclipsing binary MT Pup is 3.6 arcminutes (exceeding the positioning uncertainty range), and the flare luminosity (>${10}^{34}\mathrm{erg}/\mathrm{s}$) is much higher than that of a typical stellar flare (usually <${10}^{32}\mathrm{erg}/\mathrm{s}$)
EP250111a	97.1809	56.8983	$\mathrm{Dur}.=$ 83 s, $N_H=1.11\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =1.{01}_{+0.54}^{-0.52}$, $F_{\mathrm{obs}}=1.{39}_{+0.53}^{-0.40}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ About 4 min later, FXT autonomous observation. For FXT 0.5–10 keV: Fitted with absorbed power-law, $N_H=1.11\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =2.{42}_{+0.15}^{-0.14}$, $F_{\mathrm{obs}}=3.{43}_{+0.36}^{-0.33}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV).	Optical candidate detected
EP250125a	175.364	−21.708	For WXT, $\mathrm{Dur}.=$ 74 s, $N_H=4.15\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =0.8_{+0.5}^{-0.5}$, $F_{\mathrm{unabs}}=1.8_{+0.7}^{-0.5}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). About 2 min later, FXT autonomous observation. For FXT 0.5–10 keV: Fitted with absorbed power-law, $N_H=4.15\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =2.0_{+0.1}^{-0.1}$, $F_{\mathrm{unabs}}=5.4_{+0.6}^{-0.6}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV).	Presence of optical candidates (at r = 19.3 mag); z = 2.89
EP250207b	167.495	−7.906	$\mathrm{Dur}.>$ 120 s (before observation ended). For WXT, $N_H=4.24\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =0.6_{+0.8}^{-0.8}$, $F_{\mathrm{unabs}}=6.1_{+4.2}^{-2.5}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. FXT conducted two ToO observations: First observation: For FXT 0.5–10 keV, $N_H=4.24\times {10}^{20}{\mathrm{cm}}^{-2}$, $\Gamma =1.5_{+0.6}^{-0.6}$, $F_{\mathrm{unabs}}=3.6_{+3.5}^{-1.4}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV). Second observation: $F=6.4_{+3.5}^{-2.8}\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (flux declined)	Optical candidate detected; needs follow-up; not verified by other observations
EP250212a	114.949	60.493	$\mathrm{Dur}.\approx$ 360 s (from WXT light curve), $N_H=0.5_{+0.3}^{-0.3}\times {10}^{22}{\mathrm{cm}}^{-2}$, $\Gamma =2.2_{+1.0}^{-0.9}$, $F_{\mathrm{unabs}}=0.9_{+1.0}^{-0.3}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $F_{\mathrm{peak}}\approx 6\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. (absorbed blackbody): $N_H^{\mathrm{upper}\mathrm{limit}}=0.45\times {10}^{22}{\mathrm{cm}}^{-2}$, $T=0.6_{+0.2}^{-0.1}\mathrm{keV}$. EP-FXT follow-up ToO observation: Exposure time $t=5970$ s, about 5.6 h after EP-WXT detection. For FXT 0.5–10 keV (absorbed power-law): $N_H=6.3\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =2.1_{+0.3}^{-0.3}$, $F_{\mathrm{unabs}}=3.2_{+0.8}^{-0.7}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	No optical counterpart or other multi-band association detected
EP250220a	113.400	39.795	$\mathrm{Dur}.\approx$ 150 s, $N_H=7.13\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =1.8_{+1.0}^{-0.9}$, $F_{\mathrm{unabs}}=5.8_{+3.3}^{-2.2}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. First FXT observation: 13 h after WXT detection, exposure $\sim 3\mathrm{ks}$. In the WXT error circle, an FXT module detected a faint X-ray source. Second FXT observation: 32 h after WXT detection, exposure $\sim 7\mathrm{ks}$. No source in the WXT error circle. With $\Gamma =1.1$, $N_H=7.13\times {10}^{20}{\mathrm{cm}}^{-2}$, 0.5–10 keV upper limit is $1.90\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	No optical counterpart or other multi-band association detected
EXO 0748-676/UY Vol	117.140458	−67.752138	EXO 0748-676/UY Vol exhibited renewed X-ray activity with multiple Type-I bursts detected since June 2024, ending its 16-year quiescence since 2008. EP-WXT initially detected the source on 9 July 2024 (26 ks exposure) with $F_{\mathrm{unabs}}\sim 2.2\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV; $\Gamma =-2.0$ fixed, $N_H=1.5\times {10}^{21}{\mathrm{cm}}^{-2}$). Subsequent non-detections in July–August 2024 set $F_{\mathrm{upper}}<7.7\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. Renewed brightening was observed from 2024-10-04T22:42:34 UTC onward, with $F_{\mathrm{unabs}}$ increasing from $2.4\times {10}^{-11}$ to $4.5\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), indicating ∼20× flux enhancement compared to July levels.	Neutron star thermonuclear bursts
Optical Transients
EP240414a	191.498	−9.695	WXT: $F_{\mathrm{peak}}=3\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ FXT: $N_H=3.35\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =1.7_{-0.3}^{+0.3}$, $F_{\mathrm{unabs}}=3.5_{-0.8}^{+0.8}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV), associated with EP240414a, faded by 4 orders of magnitude in X-ray flux in 2 h since WXT detection	Optical counterpart AT2024gsa detected; later spectral evolution to SN Ic-BL; radio detection similar to long GRB
EP240426a	121.8567	−29.4609	Assuming a power-law spectrum with $\Gamma =2.0$ and galactic absorption, $F_{\mathrm{unabs}}=9.2\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV)	As an optical counterpart reported by DECam, AT 2024hfq shows obvious optical excitation characteristics, which is consistent with the electromagnetic counterpart in the context of multiple messengers. At the same time, the X-ray signal detected by EP-FXT is auxiliary information, which supports that the event is related to the merger of compact objects triggered by gravitational waves
EP250108a	55.623	−22.509	Dur. $>2500$ s. $F_{\mathrm{peak}}\sim 1.4\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). Spectrum: absorbed power-law with $\Gamma =1.35\pm 0.40$, $N_H=1.6\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=4.2_{-0.9}^{+1.2}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Associated with optical counterpart AT 2025kg, redshift $z=0.176$
EP250223a	98.258	−22.432	WXT: $\mathrm{Dur}.=140$ s, $F_{\mathrm{peak}}=2\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, $N_H=1.36\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed), $\Gamma =2.1^{\pm 0.6}$, $F_{\mathrm{unabs}}=4.4_{+1.4}^{-1.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. FXT: About 2 min later, for FXT 0.5–10 keV, $N_H=1.36\times {10}^{21}{\mathrm{cm}}^{-2}$, $\Gamma =1.{97}^{\pm 0.05}$, $F_{\mathrm{unabs}}=2.5^{\pm 0.1}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$.	Optical counterpart detected, z = 2.756
Known Sources/Unclassified
EP240309a	178.566	−50.29	WXT detected persistent emission (16 March 2024 before) with $F_{\mathrm{peak}}$ $=5$–$7\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV), upper limit $9.4\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (17 March 2024). Historical detections: XMMSL J115415.6-501758 ($F_{\mathrm{peak}}=3.5\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, 0.2–2 keV; 10 January 2022), Swift/XRT ($1.5\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, 0.3–10 keV; 20 July 2021), 1eRASS J115415.7-501758 ($3.0\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$, 0.2–2.3 keV FXT spectrum: $\Gamma =0.{95}_{-0.25}^{+0.31}$, $N_H=3.3_{-1.3}^{+2.0}\times {10}^{21}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=7.4\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.3–10 keV). Spatial association with highly variable UV/optical source Gaia DR3 5370642890382757888 ($g=14$–17; offset $<10$ arcsec), suggesting Galactic CV’s origin	Galactic CV candidate
EP240327a	203.853	7.488	Spectrum: absorbed blackbody (tbabs * bbody) with $N_H=2.7\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed), $kT={79}_{-15}^{+18}$ eV. $F_{\mathrm{unabs}}=3.5_{-0.9}^{+0.9}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4.0 keV). Source associated with nucleus of early-type galaxy SDSS J133519.91 + 072,807.4 ($z=0.0024$)	Possible AGN flare
GOTO065054.49 + 593,624.51	102.7272	59.6078	Spectrum (0.5–10 keV): absorbed power-law with $\Gamma =3.{23}_{-0.56}^{+0.68}$, $N_H=7.1_{-4.3}^{+6.8}\times {10}^{20}{\mathrm{cm}}^{-2}$. $F_{\mathrm{unabs}}=8.1_{-1.4}^{+1.9}\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Galactic WZ Sge-type dwarf nova outburst (high-amplitude optical/X-ray transient; spectra confirm Balmer/HeI absorption lines)
EP J0052.9-7230	13.215	−72.494	Associated with CXOU J005245.0-722844, WXT spectra (0.5–4 keV): absorbed blackbody with $T=0.{087}_{-0.002}^{+0.002}/0.{091}_{-0.001}^{+0.001}$ keV, $N_H=4.8\times {10}^{21}{\mathrm{cm}}^{-2}$ (fixed). Corresponding $F_{\mathrm{unabs}}=1.{76}_{-0.08}^{+0.08}/1.{52}_{-0.05}^{+0.05}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Potential neutron star/white dwarf origin
EP240709a	7.910	−56.760	WXT spectrum (0.5–4 keV): absorbed power-law with $\Gamma =0.7_{-0.6}^{+0.6}$, $N_H=1.2\times {10}^{20}{\mathrm{cm}}^{-2}$ (fixed). $F_{\mathrm{unabs}}=1.3_{-0.5}^{+0.6}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. FXT follow-up observation Spectrum: $\Gamma =2.3_{-0.2}^{+0.1}$, $N_H=1.5_{-0.4}^{+0.4}\times {10}^{21}{\mathrm{cm}}^{-2}$. $F_{\mathrm{unabs}}=6.6_{-0.3}^{+0.3}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV).	Associated with high-energy gamma-ray source 4FGL J0031.5-564
CV GD 1662	352.248	−29.749	Historical Swift/XRT observations show high variability: $F_{\mathrm{unabs}}=1.3_{-0.3}^{+0.3}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (17 October 2008) vs. $2.4_{-0.1}^{+0.1}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (10 August 2015; 0.5–10 keV). FXT spectrum: absorbed power-law with $\Gamma =1.{63}_{-0.09}^{+0.09}$. $F_{\mathrm{unabs}}=4.{65}_{-0.21}^{+0.21}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	CV flare activity
HMXB 4U 2238 + 60	339.8390	61.2729	EP/WXT detected $F_{\mathrm{obs}}\sim 1.0\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. EP/FXT follow-up (2421 s exposure) localized source at R.A. = 339.8390°, Dec. = 61.2729° (10 arcsec error radius; Assoc.: HMXB 4U 2238 + 60, 5.5 arcsec from Gaia EDR3). Historical Chandra detection (2013): $F_{\mathrm{unabs}}=3.8_{-0.4}^{+0.4}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–7 keV). FXT spectrum: $\Gamma =0.8_{-0.2}^{+0.2}$, $F_{\mathrm{unabs}}=5.4_{-0.4}^{+0.4}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV), indicating a ∼140× flux increase	HMXB outburst
PHL 1811	328.756302	−9.373429	EP/WXT detected a flare from quasar PHL 1811 (9.24 ks exposure), $F_{\mathrm{unabs}}=1.2_{-0.7}^{+0.7}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). EP/FXT follow-up (2024-08-04T14:35:25 UTC, 33 h later) confirmed association, with $\Gamma =1.{85}_{-0.29}^{+0.29}$ and $F_{\mathrm{unabs}}=5.{25}_{-0.15}^{+0.15}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV). Swift/XRT non-detection (2024-08-06T20:45:02 UTC) sets $F_{\mathrm{upper}}<1.0\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.3–10 keV). Historical fluxes: $6.8_{-0.4}^{+0.4}\times {10}^{-14}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (XMM-Newton 1 November 2004; 0.2–12 keV), $4.2_{-1.0}^{+1.0}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (Swift/XRT 22 October 2005; 0.3–10 keV). EP flare shows ∼100× flux enhancement, indicating day-timescale X-ray variability in this X-ray weak WLQ	Quasar X-ray flare
Aql X-1	287.816905	0.584963	Detected by EP-WXT: Power-law: $\Gamma =2.7_{-1.1}^{+1.6}$, $N_H=1.6_{-0.7}^{+0.9}\times {10}^{22}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=2.1_{-1.1}^{+6.5}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV); Diskbb: $kT=0.8_{-0.3}^{+0.6}$ keV, $N_H=1.1_{-0.4}^{+0.3}\times {10}^{22}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=1.1_{-0.3}^{+0.6}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. 2024-09-18T15:53:42 UTC (flux increased): Power-law: $\Gamma =1.9_{-0.3}^{+0.2}$, $N_H=1.0_{-0.2}^{+0.1}\times {10}^{22}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=6.0_{-0.7}^{+1.1}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$; Diskbb: $kT=1.1_{-0.1}^{+0.2}$ keV, $N_H=0.7_{-0.1}^{+0.1}\times {10}^{22}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=4.7_{-0.4}^{+0.4}\times {10}^{-10}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	LMXB accretion state transition
S241125n	58.079	+69.689	Duration = Following the gravitational wave event S241125n and the Swift/BAT candidate, EP/FXT conducted an 11 ks observation of the BAT localization region (R.A. = 58.079°, Dec. = +69.689°) 26 h post-trigger. Within the 5 arcmin error circle, an X-ray source EPF_J035226 + 6938 (R.A. = 58.1097°, Dec. = 69.6392°, 10 arcsec positional uncertainty) was detected, consistent with the Swift/XRT source S241125n_X3 (GCN 38324). Its spectrum is well fitted by a power-law model with $\Gamma =0.{43}_{-0.74}^{+0.76}$ ($N_H=3.4\times {10}^{21}{\mathrm{cm}}^{-2}$ fixed), yielding $F_{\mathrm{unabs}}=1.{17}_{-0.63}^{+1.18}\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV). Six additional X-ray sources were detected within a 10 arcmin radius, including three cross-matched with Swift/XRT. The brightest source, EPF_J035113 + 6949, has an observed flux of $\sim 7.7\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$	Gravitational wave counterpart candidate
RX J0032.9-7348	8.232	−37.807	Detected possible X-ray brightening of HMXB RX J0032.9-7348 (SMC) on 2024-10-27T19:36:51 UTC (5.6 ks exposure), localized at R.A. = 8.232°/−73.807° (2.2 arcmin error). Follow-up EP/FXT observations (14.5/20.9 h post-detection) confirmed a source at R.A. = 8.2249°/−73.8094° (10 arcsec precision; Assoc.: RX J0032.9-7348, 3.6 arcsec offset from Haberl & Sturm, 2016 position). Time-resolved FXT spectra show $\Gamma =0.{81}_{-0.05}^{+0.05}$, $N_H=4.8_{-2.4}^{+2.5}\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=7.{95}_{-0.30}^{+0.31}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV), ∼40× brighter than historical upper limits (RASS 1993: ∼$2\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$; XMM-Newton/Swift 2010–2024: $<{10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$), indicating a potential outburst	HMXB potential outburst
LAMOST J015016.17 + 375,618.9	27.556	37.937	Detected X-ray brightening of CV LAMOST J015016.17 + 375,618.9 on 2024-11-05T07:13:32 UTC (11.8 ks exposure), localized at R.A. = 27.556°/+37.937° (2.3 arcmin uncertainty). Stacked pre-flare data (7 September 2024) sets $F_{\mathrm{upper}}\sim 2\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$. WXT spectrum: $\Gamma =1.3_{-0.4}^{+0.7}$ ($N_H=5.2\times {10}^{20}{\mathrm{cm}}^{-2}$ fixed), $F_{\mathrm{unabs}}=7.2_{-2.7}^{+2.7}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). EP/FXT follow-up (2024-11-06T08:52:05 UTC) confirmed the source at R.A. = 27.5677°/+37.9381° (10 arcsec precision; Assoc.: CV LAMOST J015016.17 + 375,618.9, 1.9 arcsec offset) with $\Gamma =1.{53}_{-0.08}^{+0.10}$, $F_{\mathrm{unabs}}=7.{83}_{-0.21}^{+0.21}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV), ∼40× brighter than ROSAT All-Sky Survey flux ($\sim 2\times {10}^{-13}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$)	CV outburst
QX Nor	243.162	−52.404	Detected possible X-ray brightening of LMXB QX Nor (1.6 ks exposure). Spectrum: absorbed power-law with $\Gamma =1.3_{-0.4}^{+0.5}$, $N_H=9.{60}_{-2.35}^{+2.73}\times {10}^{21}{\mathrm{cm}}^{-2}$. $F_{\mathrm{unabs}}=1.0_{-0.2}^{+0.4}\times {10}^{-9}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV).	LMXB accretion flare
EP J064833.4 + 065,624	102.133	6.919	Detected a new X-ray outburst (EP J064833.4 + 065,624) associated with CV PNV J06483343 + 0,656,236. WXT spectrum: $\Gamma =4.5_{-2.1}^{+2.7}$ ($N_H=5.5\times {10}^{21}{\mathrm{cm}}^{-2}$ fixed), $F_{\mathrm{abs}}=6.0_{-3.2}^{+6.6}\times {10}^{-12}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–4 keV). Follow-up EP/FXT (2025-02-10T18:11:45 UTC) localized source at R.A. = 102.1393°/Dec. = 6.9401° (10 arcsec precision; Assoc.: PNV J06483343+0656236, 1.3 arcsec offset) with $\Gamma =1.{54}_{-0.11}^{+0.15}$, $N_H<6.5\times {10}^{20}{\mathrm{cm}}^{-2}$, $F_{\mathrm{unabs}}=1.{36}_{-0.12}^{+0.13}\times {10}^{-11}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}$ (0.5–10 keV; ∼40× brighter than ROSAT $F_{\mathrm{peak}}$ $\sim 3.5\times {10}^{-13}$). Coincident optical outburst observed since 29 January 2025 with $\Delta g\sim 4.8$ mag brightening (ASAS-SN). First X-ray detection from this CV.	CV outburst with optical counterpart

Note: In the fourth column, the following abbreviations and conventions are used: RA/Dec—Right Ascension and Declination (in degrees, J2000 epoch). EP—Einstein Probe. Dur.—Duration (seconds); values correspond to the first exposure relative to the X-ray trigger time. $F_{\mathrm{peak}}$—Peak flux in the 0.5–4 keV band (erg s⁻¹ cm⁻²). $F_{\mathrm{AG}}$—Afterglow flux in the 0.5–4 keV band (erg s⁻¹ cm⁻²), based on the first exposure. $N_H$—Hydrogen column density (cm⁻²); “fixed” indicates that the value was held constant during spectral fitting. $\Gamma$—Photon index of the power-law spectrum. $F_{\mathrm{unabs}}$—Unabsorbed flux in the 0.5–4 keV band (erg s⁻¹ cm⁻²). T—Temperature (keV), as derived from the absorbed apec model. abs apec—Absorbed Astrophysical Plasma Emission Code model (thermal plasma emission); the model assumes fixed metal abundances and follows standard fitting procedures. Assoc.—“Associated with”, indicating source classifications (e.g., M-type star, GRB, FXT, OT). X-ray L_jump—X-ray luminosity jump, representing the factor by which the X-ray luminosity increases relative to the quiescent state. WXT—Wide-field X-ray Telescope of the Einstein Probe. FXT—Follow-up X-ray Telescope of the Einstein Probe. Fixed parameters—Values marked as “fixed” were not varied during spectral fitting, typically based on prior constraints (e.g., Galactic absorption). Energy range—Unless specified, fluxes are reported in the 0.5–4 keV band. Upper limit—3$\sigma$ flux upper limit in the 0.5–4 keV band (erg s⁻¹ cm⁻²). Uncertainties represent 1 $\sigma$ errors unless otherwise noted. For missing or inapplicable data, a dash (—) is used. The coordinates listed in this table and the corresponding X-ray properties are based primarily on the initial reports provided by EP for each source. When a source’s coordinates are not available from the EP report, the coordinates from the SIMBAD catalog have been added. Furthermore, source names follow the official EP nomenclature whenever available; if no official EP name exists, the source is instead identified by the corresponding star’s name.

Table A1 in the Appendix A provides a detailed summary of the multi-wavelength follow-up observations for transient events whose names begin with “EP”. These sources are selected because they represent the initial detections by Einstein Probe that subsequently triggered coordinated observations across various wavelengths.

3.2. Notable Sources

During its first year of operation, EP detected numerous interesting X-ray transients. Here, we highlight five of them.

The first transient detected by EP was EPW20240219aa, reported during its commissioning phase [19]. Follow-up analysis suggested that this source was likely a gamma-ray burst (GRB) event, based on the detection of a coincident weak gamma-ray transient in Fermi/GBM data [20]. This source was subsequently identified as an untriggered gamma-ray burst through archival searches in Fermi/GBM, Swift/BAT, and Insight-HXMT/HE data. The joint spectral analysis revealed that a single cutoff power-law model could well describe both X-ray and gamma-ray bands, with a photon index of $-1.70\pm 0.05$ and a peak energy of $257\pm 134$ keV, classifying it as an X-ray rich GRB. The analysis of prompt emission suggested a Poynting flux-dominated outflow rather than a thermal photon-dominated one. While follow-up observations in optical and radio bands identified several candidates, none was confirmed as the afterglow counterpart [21]. This discovery not only marked EP’s first light but also demonstrated its capability in detecting and characterizing the soft X-ray emission of GRBs.

A particularly remarkable discovery was EP240315a, detected on 15 March 2024, which represents one of the most distant high-energy transients observed by EP, at a redshift of $z=4.859$ [22]. This event exhibited strikingly different temporal profiles between its soft X-ray and gamma-ray emissions—while the gamma-ray emission observed by Swift/BAT and Konus-Wind lasted approximately 40 s, the soft X-ray emission detected by EP-WXT persisted for over 1000 s, making it one of the longest GRB durations ever measured [23]. High-redshift GRBs provide crucial insights into the early universe, serving as beacons to probe the formation of the first-generation stars and the reionization epoch. EP240315a joins this class, which includes GRB 090423 ($z=8.2$) [5,24], further extending the sample of high-redshift bursts accessible to soft X-ray observations. Multi-wavelength follow-up observations revealed a relativistic jet with a half-opening angle of approximately $3^{\circ }$ and a beaming-corrected total energy of ∼$4\times {10}^{51}$ erg, typical of long GRBs [25]. The optical counterpart was detected by ATLAS approximately 1.3 h after the initial X-ray trigger, showing rapid fading behavior with a decay of ∼2 magnitudes within 19 h, while the radio counterpart was detected 2.86 days post-burst using the MeerKAT radio telescope, revealing emission consistent with optically thick synchrotron radiation. The combination of multi-wavelength observations suggested EP240315a originated from a highly relativistic event, likely either a long gamma-ray burst or a jetted tidal disruption event, and demonstrated that some FXTs could be related to the lower-luminosity end of the GRB population [26]. This discovery highlights EP’s capability to probe the high-redshift transient universe, complementing existing missions and potentially uncovering the population of early-universe X-ray transients.

Another intriguing discovery was EP240408a, detected on 8 April 2024, which represents a new class of X-ray transients with an intermediate timescale [27]. The source exhibited a peculiar light curve featuring a 12 s intense X-ray flare that reached a peak flux of $3.9\times {10}^{-9}$ erg cm⁻² s⁻¹ in the 0.5–4 keV energy band, approximately 300 times brighter than its underlying emission [27]. Further analysis revealed that at redshift z > 0.5, this corresponds to a peak luminosity of ∼${10}^{49}$ erg s⁻¹ [11]. The X-ray emission showed a plateau phase lasting for 4 days with luminosity exceeding ${10}^{46}$ erg s⁻¹, followed by a steep decay ($\propto t^{-7}$) [11]. Extensive multi-wavelength follow-up observations revealed no optical or radio counterparts, though a faint potential host galaxy (r ∼ 24 AB mag) was identified near the X-ray localization [11]. The source’s X-ray spectrum remained non-thermal throughout the outburst, with a power-law photon index varying between 1.8–2.5 [27]. The observed properties of EP240408a were found to be inconsistent with known transient types—notably, the lack of a bright gamma-ray counterpart conflicts with typical gamma-ray bursts of similar X-ray luminosities, suggesting it may represent either a peculiar jetted tidal disruption event at z > 1.0 or an entirely new class of X-ray transients [11].

EP240414a, discovered on 14 April 2024, represents a highly unique fast X-ray transient. Located at a redshift of $z=0.4018$, it showed an unusually large offset (approximately 26–27 kpc) from its spiral host galaxy [28]. The source exhibited a complex, multi-component light curve featuring an initial rapid decline, followed by an unusual re-brightening reaching an absolute magnitude $M_r\sim -21$ after two rest-frame days [29]. In the radio band, the source peaked around 30 days post-explosion with luminosity comparable to long gamma-ray bursts (∼$2\times {10}^{30}$ erg s⁻¹ Hz⁻¹), indicating a moderately relativistic outflow (bulk Lorentz factor $\Gamma \gtrsim 1.6$) [30]. The source eventually revealed a broad-lined Type Ic supernova component, and while it shared some characteristics with luminous fast blue optical transients (LFBOTs), its distinctive red colors and high X-ray luminosity (∼${10}^{48}$ erg s⁻¹) suggested different physical mechanisms [31]. This remarkable source represents a previously unknown population of extragalactic fast X-ray transients, bridging the gap between classical gamma-ray bursts and ordinary stripped-envelope supernovae.

EP240709a, discovered by EP on 9 July 2024, represents a distinctive blazar candidate exhibiting remarkable characteristics. Its most notable feature is an extraordinary orphan X-ray flare, where the flux in the 0.5–10 keV energy band increased by at least 28 times compared to its low state in 2020, while showing no significant variability in radio, infrared, optical, UV, and GeV bands [32]. Subsequent NICER monitoring revealed X-ray flux variations between $(3-9)\times {10}^{-12}$ erg s⁻¹ cm⁻² in the 0.4–3.0 keV band, and multiple lines of evidence support its classification as a high-frequency-peaked BL Lac object, including its spatial coincidence with the Fermi unassociated source 4FGL J0031.5-5648 and a 99.98% probability of being a quasar as revealed by Gaia DR3 machine learning classification [33]. This discovery demonstrates Einstein Probe’s capability in identifying peculiar activities from active galactic nuclei through high-cadence X-ray sky surveys.

4. Conclusions

The first year of Einstein Probe (EP) operations has not only validated its unique capabilities in monitoring the dynamic X-ray sky but also yielded critical insights into high-energy transient phenomena, thanks to the capability of rapidly disseminating high-energy alerts associated with early follow-up observations, such as the ones carried out with our BOOTES network.

Out of the 128 events, the BOOTES network has been able to follow up on 58 events, detecting 6 optical counterparts at early times (EP240309a, EP trigger ID 01708981728, EP240804a, EP241109a, GRB 241105A, and EP trigger ID 01709128948).

While EP delivered outstanding results in its inaugural year, continued improvements in data processing, calibration, and real-time alert dissemination will further enhance its scientific yield. Moreover, coordinated multi-wavelength and multi-messenger follow-up observations remain essential for fully characterizing the diverse transient phenomena uncovered by EP. In this regard, we expect the early-time follow-up by the BOOTES Global Network (and other facilities) will enhance the overall picture of the transients discovered by EP.

As time-domain and multi-messenger astronomy continue to evolve, EP’s first-year contributions firmly establish it as a key observatory for unveiling the transient X-ray universe, effectively bridging the gap between current and next-generation high-energy missions.