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Keywords = gravitational waves: sources

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26 pages, 2204 KiB  
Review
Recent Advances in Understanding R-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems
by Avrajit Bandyopadhyay and Timothy C. Beers
Universe 2025, 11(7), 229; https://doi.org/10.3390/universe11070229 - 11 Jul 2025
Viewed by 279
Abstract
The rapid neutron-capture process (r-process) is responsible for the creation of roughly half of the elements heavier than iron, including precious metals like silver, gold, and platinum, as well as radioactive elements such as thorium and uranium. Despite its importance, the [...] Read more.
The rapid neutron-capture process (r-process) is responsible for the creation of roughly half of the elements heavier than iron, including precious metals like silver, gold, and platinum, as well as radioactive elements such as thorium and uranium. Despite its importance, the nature of the astrophysical sites where the r-process occurs, and the detailed mechanisms of its formation, remain elusive. The key to resolving these mysteries lies in the study of chemical signatures preserved in ancient, metal-poor stars. These stars, which formed in the early Universe, retain the chemical fingerprints of early nucleosynthetic events and offer a unique opportunity to trace the origins of r-process elements in the early Galaxy. In this review, we explore the state-of-the-art understanding of r-process nucleosynthesis, focusing on the sites, progenitors, and formation mechanisms. We discuss the role of potential astrophysical sites such as neutron star mergers, core-collapse supernovae, magneto-rotational supernovae, and collapsars, that can play a key role in producing the heavy elements. We also highlight the importance of studying these signatures through high-resolution spectroscopic surveys, stellar archaeology, and multi-messenger astronomy. Recent advancements, such as the gravitational wave event GW170817 and detection of the r-process in the ejecta of its associated kilonovae, have established neutron star mergers as one of the confirmed sites. However, questions remain regarding whether they are the only sites that could have contributed in early epochs or if additional sources are needed to explain the signatures of r-process found in the oldest stars. Additionally, there are strong indications pointing towards additional sources of r-process-rich nuclei in the context of Galactic evolutionary timescales. These are several of the outstanding questions that led to the formation of collaborative efforts such as the R-Process Alliance, which aims to consolidate observational data, modeling techniques, and theoretical frameworks to derive better constraints on deciphering the astrophysical sites and timescales of r-process enrichment in the Galaxy. This review summarizes what has been learned so far, the challenges that remain, and the exciting prospects for future discoveries. The increasing synergy between observational facilities, computational models, and large-scale surveys is poised to transform our understanding of r-process nucleosynthesis in the coming years. Full article
(This article belongs to the Special Issue Advances in Nuclear Astrophysics)
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22 pages, 12185 KiB  
Article
Airborne Strapdown Gravity Survey of Sos Enattos Area (NE Sardinia, Italy): Insights into Geological and Geophysical Characterization of the Italian Candidate Site for the Einstein Telescope
by Filippo Muccini, Filippo Greco, Luca Cocchi, Maria Marsella, Antonio Zanutta, Alessandra Borghi, Matteo Cagnizi, Daniele Carbone, Mauro Coltelli, Danilo Contrafatto, Peppe Junior Valentino D’Aranno, Luca Frasca, Alfio Alex Messina, Luca Timoteo Mirabella, Monia Negusini and Eleonora Rivalta
Remote Sens. 2025, 17(13), 2309; https://doi.org/10.3390/rs17132309 - 5 Jul 2025
Viewed by 357
Abstract
Strapdown gravity systems are increasingly employed in airborne geophysical exploration and geodetic studies due to advantages such as ease of installation, wide dynamic range, and adaptability to various platforms, including airplanes, helicopters, and large drones. This study presents results from an airborne gravity [...] Read more.
Strapdown gravity systems are increasingly employed in airborne geophysical exploration and geodetic studies due to advantages such as ease of installation, wide dynamic range, and adaptability to various platforms, including airplanes, helicopters, and large drones. This study presents results from an airborne gravity survey conducted over the northeastern sector of Sardinia (Italy), using a high-resolution strapdown gravity ensuring an accuracy of approximately 1 mGal. Data were collected at an average altitude of 1800 m with a spatial resolution of 3.0 km. The survey focused on the Sos Enattos area near Lula (Nuoro province), a candidate site for the Einstein Telescope (ET), a third-generation gravitational wave observatory. The ideal site is required to be geologically and seismically stable with a well-characterized subsurface. To support this, we performed a new gravity survey to complement existing geological and seismic data aimed at characterizing the mid-to-shallow crustal structure of Sos Enattos. Results show that the strapdown system effectively detects gravity anomalies linked to crustal sources down to ~3.5 km, with particular emphasis within the 1–2 km depth range. Airborne gravity data reveal higher frequency anomalies than those resolved by the EGM2008 global gravity model and show good agreement with local terrestrial gravity data. Forward modeling of the gravity field suggests a crust dominated by alternating high-density metamorphic rocks and granitoid intrusions of the Variscan basement. These findings enhance the geophysical understanding of Sos Enattos and support its candidacy for the ET site. Full article
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23 pages, 337 KiB  
Article
A Spacetime Metric for the 4 + 1 Formalism
by Martin Land
Sci 2025, 7(3), 86; https://doi.org/10.3390/sci7030086 - 1 Jul 2025
Viewed by 253
Abstract
In his foundational work on classical and quantum electrodynamics, Stueckelberg introduced an external evolution parameter, τ, in order to overcome difficulties associated with the problem of time in relativity. Stueckelberg particle trajectories are described by the evolution of spacetime events under the [...] Read more.
In his foundational work on classical and quantum electrodynamics, Stueckelberg introduced an external evolution parameter, τ, in order to overcome difficulties associated with the problem of time in relativity. Stueckelberg particle trajectories are described by the evolution of spacetime events under the monotonic advance of τ, the basis for the Feynman–Stueckelberg interpretation of particle–antiparticle interactions. An event is a solution to τ-parameterized equations of motion, which, under simple conditions, including the elimination of pair processes, can be reparameterized by the proper time of motion. The 4+1 formalism in general relativity (GR) extends this framework to provide field equations for a τ-dependent local metric γμν(x,τ) induced by these Stueckelberg trajectories, leading to τ-parameterized geodesic equations in an evolving spacetime. As in standard GR, the linearized theory for weak fields leads to a wave equation for the local metric induced by a given matter source. While previous attempts to solve the wave equation have produced a metric with the expected features, the resulting geodesic equations for a test particle lead to unreasonable trajectories. In this paper, we discuss the difficulties associated with the wave equation and set up the more general ADM-like 4+1 evolution equations, providing an initial value problem for the metric induced by a given source. As in the familiar 3+1 formalism, the metric can be found as a perturbation to an exact solution for the metric induced by a known source. Here, we propose a metric, ansatz, with certain expected properties; obtain the source that induces this metric; and use them as the initial conditions in an initial value problem for a general metric posed as a perturbation to the ansatz. We show that the ansatz metric, its associated source, and the geodesic equations for a test particle behave as required for such a model, recovering Newtonian gravitation in the nonrelativistic limit. We then pose the initial value problem to obtain more general solutions as perturbations of the ansatz. Full article
10 pages, 5511 KiB  
Review
Multimessenger Studies with the Pierre Auger Observatory
by Jon Paul Lundquist and the Pierre Auger Collaboration
Particles 2025, 8(2), 45; https://doi.org/10.3390/particles8020045 - 22 Apr 2025
Viewed by 607
Abstract
The Pierre Auger Observatory, the world’s largest ultra-high-energy (UHE) cosmic ray (CR) detector, plays a crucial role in multi-messenger astroparticle physics with its high sensitivity to UHE photons and neutrinos. Recent Auger Observatory studies have set stringent limits on the diffuse and point-like [...] Read more.
The Pierre Auger Observatory, the world’s largest ultra-high-energy (UHE) cosmic ray (CR) detector, plays a crucial role in multi-messenger astroparticle physics with its high sensitivity to UHE photons and neutrinos. Recent Auger Observatory studies have set stringent limits on the diffuse and point-like fluxes of these particles, enhancing constraints on dark-matter models and UHECR sources. Although no temporal coincidences of neutrinos or photons with LIGO/Virgo gravitational wave events have been observed, competitive limits on the energy radiated in these particles have been established, particularly from the GW170817 binary neutron star merger. Additionally, correlations between the arrival directions of UHECRs and high-energy neutrinos have been explored using data from the IceCube Neutrino Observatory, ANTARES, and the Auger Observatory, providing additional neutrino flux constraints. Efforts to correlate UHE neutron fluxes with gamma-ray sources within our galaxy continue, although no significant excesses have been found. These collaborative and multi-faceted efforts underscore the pivotal role of the Auger Observatory in advancing multi-messenger astrophysics and probing the most extreme environments of the Universe. Full article
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32 pages, 3983 KiB  
Article
Parameter Estimation Precision with Geocentric Gravitational Wave Interferometers: Monochromatic Signals
by Manoel Felipe Sousa, Tabata Aira Ferreira and Massimo Tinto
Universe 2025, 11(4), 122; https://doi.org/10.3390/universe11040122 - 7 Apr 2025
Viewed by 429
Abstract
We present a Fisher information matrix study of the parameter estimation precision achievable by a class of future space-based, “mid-band”, gravitational wave interferometers observing monochromatic signals. The mid-band is the frequency region between that accessible by the Laser Interferometer Space Antenna (LISA) and [...] Read more.
We present a Fisher information matrix study of the parameter estimation precision achievable by a class of future space-based, “mid-band”, gravitational wave interferometers observing monochromatic signals. The mid-band is the frequency region between that accessible by the Laser Interferometer Space Antenna (LISA) and ground-based interferometers. We analyze monochromatic signals observed by the TianQin mission, gLISA (a LISA-like interferometer in a geosynchronous orbit) and a descoped gLISA mission, gLISAd, characterized by an acceleration noise level that is three orders of magnitude worse than that of gLISA. We find that all three missions achieve their best angular source reconstruction precision in the higher part of their accessible frequency band, with an error box better than 1010 sr in the frequency band [101,10] Hz when observing a monochromatic gravitational wave signal of amplitude h0=1021 that is incoming from a given direction. In terms of their reconstructed frequencies and amplitudes, TianQin achieves its best precision values in both quantities in the frequency band [102,4×101] Hz, with a frequency precision σfgw=2×1011 Hz and an amplitude precision σh0=2×1024. gLISA matches these precisions in a frequency band slightly higher than that of TianQin, [3×102,1] Hz, as a consequence of its smaller arm length. gLISAd, on the other hand, matches the performance of gLISA only over the narrower frequency region, [7×101,1] Hz, as a consequence of its higher acceleration noise at lower frequencies. The angular, frequency, and amplitude precisions as functions of the source sky location are then derived by assuming an average signal-to-noise ratio of 10 at a selected number of gravitational wave frequencies covering the operational bandwidth of TianQin and gLISA. Similar precision functions are then derived for gLISAd by using the amplitudes resulting in the gLISA average SNR being equal to 10 at the selected frequencies. We find that, for any given source location, all three missions display a marked precision improvement in the three reconstructed parameters at higher gravitational wave frequencies. Full article
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49 pages, 5523 KiB  
Review
Gamma-Ray Bursts: The Energy Monsters of the Universe
by Franco Giovannelli
Galaxies 2025, 13(2), 16; https://doi.org/10.3390/galaxies13020016 - 25 Feb 2025
Viewed by 2557
Abstract
Gamma-Ray Bursts(GRBs) are the most violent and energetic astrophysical phenomena, which I dare call “the Energy Monsters of the Universe”. Indeed, they show an enormous emitted isotropic energy ranging from ∼3 × 1046 erg (GRB 170817A) to ∼1055 [...] Read more.
Gamma-Ray Bursts(GRBs) are the most violent and energetic astrophysical phenomena, which I dare call “the Energy Monsters of the Universe”. Indeed, they show an enormous emitted isotropic energy ranging from ∼3 × 1046 erg (GRB 170817A) to ∼1055 erg (GRB 221009A) and a duration ranging from ≈milliseconds to ∼104 s. In this review—which I agreed to write as a scientist not directly involved in the field of GRBs—I will present the history of GRBs from the time of their discovery by chance until the new era whose beginning was marked by the detection of gravitational waves coming from the merger of two neutron stars. I will discuss the experimental results and their physical interpretation, which is still a source of heated debate within the scientific community. Due to the reasonable length of this review and especially given my limited knowledge, I do not claim to have exhausted the complicated topic of GRBs, but to have contributed in making this subject easy to read for non-experts, providing a critical contribution that is hopefully useful to the whole community. Full article
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20 pages, 909 KiB  
Article
Where to Search for Supermassive Binary Black Holes
by Paola Marziani, Edi Bon, Natasa Bon and Mauro D’Onofrio
Universe 2025, 11(3), 76; https://doi.org/10.3390/universe11030076 - 21 Feb 2025
Viewed by 647
Abstract
Supermassive binary black holes (SMBBHs) are the anticipated byproducts of galaxy mergers and play a pivotal role in shaping galaxy evolution, gravitational wave emissions, and accretion physics. Despite their theoretical prevalence, direct observational evidence for SMBBHs remains elusive, with only a handful of [...] Read more.
Supermassive binary black holes (SMBBHs) are the anticipated byproducts of galaxy mergers and play a pivotal role in shaping galaxy evolution, gravitational wave emissions, and accretion physics. Despite their theoretical prevalence, direct observational evidence for SMBBHs remains elusive, with only a handful of candidates identified to date. This paper explores optimal strategies and key environments for locating SMBBHs, focusing on observational signatures in the broad Balmer lines. We present a preliminary analysis on a flux-limited sample of sources belonging to an evolved spectral type along the quasar main sequence, and we discuss the spectroscopic clues indicative of binary activity and highlight the critical role of time-domain spectroscopic surveys in uncovering periodic variability linked to binary systems. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
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9 pages, 1558 KiB  
Article
Magnetic Noise Mitigation Strategies for the Einstein Telescope Infrastructure
by Barbara Garaventa, Federico Armato, Andrea Chincarini and Irene Fiori
Galaxies 2025, 13(1), 9; https://doi.org/10.3390/galaxies13010009 - 31 Jan 2025
Cited by 1 | Viewed by 793
Abstract
The Einstein Telescope (ET) will be a third-generation Gravitational Wave (GW) detector that will tackle cutting-edge technological challenges. The ET will be constructed at a depth of 200–300 m to isolate it from vibrations caused by seismic waves and human activities, which are [...] Read more.
The Einstein Telescope (ET) will be a third-generation Gravitational Wave (GW) detector that will tackle cutting-edge technological challenges. The ET will be constructed at a depth of 200–300 m to isolate it from vibrations caused by seismic waves and human activities, which are sources of noise for GW detection. To meet the ET’s objectives, it will be necessary to improve low-frequency sensitivity by about two orders of magnitude compared to current interferometers (LIGO, Virgo). Magnetic noise is a limiting noise in the frequency range from a few Hz up to around 100 Hz in future GW detectors. This article will discuss the magnetic noise mitigation strategies under development, based on experiences from Virgo. Full article
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22 pages, 3351 KiB  
Article
Distinguishing Compact Objects in Extreme-Mass-Ratio Inspirals by Gravitational Waves
by Lujia Xu, Shucheng Yang, Wenbiao Han, Xingyu Zhong, Rundong Tang and Yuanhao Zhang
Universe 2025, 11(1), 18; https://doi.org/10.3390/universe11010018 - 13 Jan 2025
Cited by 2 | Viewed by 1363
Abstract
Extreme-mass-ratio inspirals (EMRIs) are promising gravitational-wave (GW) sources for space-based GW detectors. EMRI signals typically have long durations, ranging from several months to several years, necessitating highly accurate GW signal templates for detection. In most waveform models, compact objects in EMRIs are treated [...] Read more.
Extreme-mass-ratio inspirals (EMRIs) are promising gravitational-wave (GW) sources for space-based GW detectors. EMRI signals typically have long durations, ranging from several months to several years, necessitating highly accurate GW signal templates for detection. In most waveform models, compact objects in EMRIs are treated as test particles without accounting for their spin, mass quadrupole, or tidal deformation. In this study, we simulate GW signals from EMRIs by incorporating the spin and mass quadrupole moments of the compact objects. We evaluate the accuracy of parameter estimation for these simulated waveforms using the Fisher Information Matrix (FIM) and find that the spin, tidal-induced quadruple, and spin-induced quadruple can all be measured with precision ranging from 102 to 101, particularly for a mass ratio of ∼104. Assuming the “true” GW signals originate from an extended body inspiraling into a supermassive black hole, we compute the signal-to-noise ratio (SNR) and Bayes factors between a test-particle waveform template and our model, which includes the spin and quadrupole of the compact object. Our results show that the spin of compact objects can produce detectable deviations in the waveforms across all object types, while tidal-induced quadrupoles are only significant for white dwarfs, especially in cases approaching an intermediate-mass ratio. Spin-induced quadrupoles, however, have negligible effects on the waveforms. Therefore, our findings suggest that it is possible to distinguish primordial black holes from white dwarfs, and, under certain conditions, neutron stars can also be differentiated from primordial black holes. Full article
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13 pages, 2989 KiB  
Article
Torsion Pendulum Apparatus for Ground Testing of Space Inertial Sensor
by Shaoxin Wang, Zuolei Wang, Dongxu Liu, Peng Dong, Jian Min, Ziren Luo, Keqi Qi and Jungang Lei
Sensors 2024, 24(23), 7816; https://doi.org/10.3390/s24237816 - 6 Dec 2024
Viewed by 1389
Abstract
The precise movement of the test mass along a geodesic is crucial for gravitational wave detection in space. To maintain this motion, the core payload-inertial sensor incorporates multiple functional units designed to mitigate various sources of stray force noise affecting the test mass. [...] Read more.
The precise movement of the test mass along a geodesic is crucial for gravitational wave detection in space. To maintain this motion, the core payload-inertial sensor incorporates multiple functional units designed to mitigate various sources of stray force noise affecting the test mass. Understanding the limits of these noise sources is essential for enhancing the inertial sensor system design. Additionally, thorough ground-based verification of these functional units is necessary to ensure their reliability for space missions. To address these challenges, we developed a low-frequency torsion pendulum apparatus that utilizes a commercial autocollimator as the optical readout element for testing this type of space inertial sensor. This paper provides a comprehensive overview of the apparatus’s operating principle, structural characteristics, and the results of laboratory tests of its background noise. Experimental data demonstrate that the torsion pendulum achieves a sensitivity of 1 × 10−11 Nm/Hz1/2 within the measurement band from 1 mHz to 0.1 Hz, confirming its suitability for various inertial sensor tests. Furthermore, the insights gained from constructing the torsion pendulum will inform future system upgrades. Full article
(This article belongs to the Special Issue Advanced Inertial Sensors: Advances, Challenges and Applications)
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31 pages, 1408 KiB  
Article
Black Hole Solutions in Non-Minimally Coupled Weyl Connection Gravity
by Maria Margarida Lima and Cláudio Gomes
Universe 2024, 10(11), 433; https://doi.org/10.3390/universe10110433 - 20 Nov 2024
Viewed by 1017
Abstract
Schwarzschild and Reissner–Nordstrøm black hole solutions are found in the context of a non-minimal matter–curvature coupling with Weyl connection both in vacuum and in the presence of a cosmological constant-like matter content. This model has the advantage of an extra force term which [...] Read more.
Schwarzschild and Reissner–Nordstrøm black hole solutions are found in the context of a non-minimal matter–curvature coupling with Weyl connection both in vacuum and in the presence of a cosmological constant-like matter content. This model has the advantage of an extra force term which can mimic dark matter and dark energy, and simultaneously following Weyl’s idea of unifying gravity and electromagnetism. In fact, vacuum Schwarzschild solutions differ from the ones in a constant curvature scenario in f(R) theories, with the appearance of a coefficient in the term that is linear in r and a corrected “cosmological constant”. Non-vacuum Schwarzschild solutions formally have the same solutions as in the previous case, with the exception being the physical interpretation of a cosmological constant as the source of the matter Lagrangian and not a simple reparameterization of the f(R) description. Reissner–Nordstrøm solutions cannot be found in a vacuum, only in the presence of matter fields, with the result that the solutions also differ from the constant curvature scenario in f(R) theories by the term being linear in r, the corrected/dressed charge, and the cosmological constant. These results have bearings on future numerical simulations for black holes and gravitational waves in next-generation wavelet templates. Full article
(This article belongs to the Section Gravitation)
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15 pages, 3604 KiB  
Article
Off-Axis Color Characteristics of Binary Neutron Star Merger Events: Applications for Space Multi-Band Variable Object Monitor and James Webb Space Telescope
by Hongyu Gong, Daming Wei and Zhiping Jin
Universe 2024, 10(10), 403; https://doi.org/10.3390/universe10100403 - 19 Oct 2024
Viewed by 1115
Abstract
With advancements in gravitational wave detection technology, an increasing number of binary neutron star (BNS) merger events are expected to be detected. Due to the narrow opening angle of jet cores, many BNS merger events occur off-axis, resulting in numerous gamma-ray bursts (GRBs) [...] Read more.
With advancements in gravitational wave detection technology, an increasing number of binary neutron star (BNS) merger events are expected to be detected. Due to the narrow opening angle of jet cores, many BNS merger events occur off-axis, resulting in numerous gamma-ray bursts (GRBs) going undetected. Models suggest that kilonovae, which can be observed off-axis, offer more opportunities to be detected in the optical/near-infrared band as electromagnetic counterparts of BNS merger events. In this study, we calculate kilonova emission using a three-dimensional semi-analytical code and model the GRB afterglow emission with the open-source Python package afterglowpy at various inclination angles. Our results show that it is possible to identify the kilonova signal from the observed color evolution of BNS merger events. We also deduce the optimal observing window for SVOM/VT and JWST/NIRCam, which depends on the viewing angle, jet opening angle, and circumburst density. These parameters can be cross-checked with the multi-band afterglow fitting. We suggest that kilonovae are more likely to be identified at larger inclination angles, which can also help determine whether the observed signals without accompanying GRBs originate from BNS mergers. Full article
(This article belongs to the Special Issue Studies in Neutron Stars)
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18 pages, 766 KiB  
Review
Time-Delay Interferometry: The Key Technique in Data Pre-Processing Analysis of Space-Based Gravitational Waves
by Pan-Pan Wang and Cheng-Gang Shao
Universe 2024, 10(10), 398; https://doi.org/10.3390/universe10100398 - 16 Oct 2024
Viewed by 1351
Abstract
Space gravitational wave detection primarily focuses on the rich wave sources corresponding to the millihertz frequency band, which provide key information for studying the fundamental physics of cosmology and astrophysics. However, gravitational wave signals are extremely weak, and any noise during the detection [...] Read more.
Space gravitational wave detection primarily focuses on the rich wave sources corresponding to the millihertz frequency band, which provide key information for studying the fundamental physics of cosmology and astrophysics. However, gravitational wave signals are extremely weak, and any noise during the detection process could potentially overwhelm the gravitational wave signals. Therefore, data pre-processing is necessary to suppress the main noise sources. Among the various noise sources, laser phase noise is dominant, approximately seven orders of magnitude larger in strength than typical gravitational wave signals, and requires suppression using time-delay interferometry (TDI) techniques, which involve combining raw data with time delays. This paper will be based on the basic principles of TDI to present methods for obtaining multi-type TDI combinations, including algebraic methods for solving indeterminate equations and geometric methods for symbolic search. Furthermore, the applicability of TDI under actual operating conditions will be considered, such as the arm locking in conjunction with the TDI algorithm. Finally, the sensitivity functions for different types of TDI combinations will be provided, which can be used to evaluate the signal-to-noise ratio (SNRs) of different TDI combinations. Full article
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31 pages, 2024 KiB  
Article
Prospects for Time-Domain and Multi-Messenger Science with AXIS
by Riccardo Arcodia, Franz E. Bauer, S. Bradley Cenko, Kristen C. Dage, Daryl Haggard, Wynn C. G. Ho, Erin Kara, Michael Koss, Tingting Liu, Labani Mallick, Michela Negro, Pragati Pradhan, J. Quirola-Vásquez, Mark T. Reynolds, Claudio Ricci, Richard E. Rothschild, Navin Sridhar, Eleonora Troja and Yuhan Yao
Universe 2024, 10(8), 316; https://doi.org/10.3390/universe10080316 - 2 Aug 2024
Cited by 7 | Viewed by 3069
Abstract
The Advanced X-ray Imaging Satellite (AXIS) promises revolutionary science in the X-ray and multi-messenger time domain. AXIS will leverage excellent spatial resolution (<1.5 arcsec), sensitivity (80× that of Swift), and a large collecting area (5–10× that of Chandra) across a 24-arcmin [...] Read more.
The Advanced X-ray Imaging Satellite (AXIS) promises revolutionary science in the X-ray and multi-messenger time domain. AXIS will leverage excellent spatial resolution (<1.5 arcsec), sensitivity (80× that of Swift), and a large collecting area (5–10× that of Chandra) across a 24-arcmin diameter field of view at soft X-ray energies (0.3–10.0 keV) to discover and characterize a wide range of X-ray transients from supernova-shock breakouts to tidal disruption events to highly variable supermassive black holes. The observatory’s ability to localize and monitor faint X-ray sources opens up new opportunities to hunt for counterparts to distant binary neutron star mergers, fast radio bursts, and exotic phenomena like fast X-ray transients. AXIS will offer a response time of <2 h to community alerts, enabling studies of gravitational wave sources, high-energy neutrino emitters, X-ray binaries, magnetars, and other targets of opportunity. This white paper highlights some of the discovery science that will be driven by AXIS in this burgeoning field of time domain and multi-messenger astrophysics. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at the AXIS website. Full article
(This article belongs to the Section Galaxies and Clusters)
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22 pages, 648 KiB  
Article
RisingTides: An Analytic Modeling Code of Tidal Effects in Binary Neutron Star Mergers
by Alexander O’Dell and Maria C. Babiuc Hamilton
Astronomy 2024, 3(3), 167-188; https://doi.org/10.3390/astronomy3030011 - 2 Jul 2024
Viewed by 2156
Abstract
Gravitational waves produced by binary neutron star mergers offer a unique window into matter behavior under extreme conditions. In this context, we analytically model the effect of matter on gravitational waves from binary neutron star mergers. We start with a binary black hole [...] Read more.
Gravitational waves produced by binary neutron star mergers offer a unique window into matter behavior under extreme conditions. In this context, we analytically model the effect of matter on gravitational waves from binary neutron star mergers. We start with a binary black hole system, leveraging the post-Newtonian formalism for the inspiral and the Backwards-one-Body model for the merger. We combine the two methods to generate a baseline waveform and we validate our results against numerical relativity simulations. Next, we integrate tidal effects in phase and amplitude to account for matter and spacetime interaction using the NRTidal model and test its accuracy against numerical relativity predictions for two equations of state, finding a mismatch around the merger. Subsequently, we lift the restriction on the coefficients to be independent of the tidal deformability and recalibrate them using the numerical relativity predictions. We obtain better fits for phase and amplitude around the merger and are able to extend the phase modeling beyond the merger. We implement our method in new open-source, user-friendly Python code, steered by a Jupyter Notebook, named RisingTides. Our research offers new perspectives on analytically modeling the effect of tides on the gravitational waves from binary neutron star mergers. Full article
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