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17 pages, 1454 KiB

Open AccessArticle

Explaining the Multiwavelength Emission of γ-ray Bright Flat-Spectrum Radio Quasar 3C 454.3 in Different Activity States

by Yaru Feng, Shaoming Hu, Ruixin Zhou and Songbo Gao

Universe 2022, 8(11), 585; https://doi.org/10.3390/universe8110585 - 04 Nov 2022

Viewed by 1172

Abstract

The origin of gamma-ray flares of blazars is still an open issue in jet physics. In this work, we reproduce the multiwavelength spectral energy distribution (SED) of flat-spectrum radio quasars 3C 454.3 under a one-zone leptonic scenario, investigate the variation of the physical [...] Read more.

The origin of gamma-ray flares of blazars is still an open issue in jet physics. In this work, we reproduce the multiwavelength spectral energy distribution (SED) of flat-spectrum radio quasars 3C 454.3 under a one-zone leptonic scenario, investigate the variation of the physical parameters in different activity states, and analyze the possible origin of its

γ

-ray outburst. Based on the analysis of multiwavelength quasi-simultaneous observations of 3C 454.3 during MJD 55,400–56,000, we consider that the radiation includes synchrotron (Syn), synchrotron self-Compton (SSC), and external Compton (EC) radiations by the simulation, and the seed photons of the external Compton component mainly comes from the broad-line region and dusty molecular torus. The model results show that: (1) We can well reproduce the multiwavelength quasi-simultaneity SED of 3C 454.3 in various activity states by using a one-zone Syn+SSC+EC model. (2) By comparing the physical model parameters of the bright and the quiescent states, we suggest that this

γ

-ray flaring activity is more likely to be caused by the increase in the doppler factor. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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13 pages, 2743 KiB

Open AccessArticle

Study of Intra-Day Flux Distributions of Blazars Using XMM-Newton Satellite

by Kiran Wani and Haritma Gaur

Universe 2022, 8(11), 578; https://doi.org/10.3390/universe8110578 - 02 Nov 2022

Viewed by 980

Abstract

We present a study of the flux distribution of a sample of 15 Intermediate and Low-energy peaked blazars using XMM-Newton observations in a total of 57 epochs on short-term timescales. We characterise the X-ray variability of all of the light curves using excess [...] Read more.

We present a study of the flux distribution of a sample of 15 Intermediate and Low-energy peaked blazars using XMM-Newton observations in a total of 57 epochs on short-term timescales. We characterise the X-ray variability of all of the light curves using excess fractional variability amplitude and found that only 24 light curves in 7 sources are significantly variable. In order to characterise the origin of X-ray variability in these blazars, we fit the flux distributions of all these light curves using Gaussian and lognormal distributions, as any non-Gaussian perturbation could indicate the imprints of fluctuations in the accretion disc, which could be Doppler boosted through the relativistic jets in blazars. However, intra-day variability, as seen in our observations, is difficult to reconcile using disc components as the emissions in such sources are mostly dominated by jets. We used Anderson–Darling (AD) and

χ^{2}

tests to fit the histograms. In 11 observations of 4 blazars, namely, ON 231, 3C 273, PKS 0235+164 and PKS 0521-365, both models equally fit the flux distributions. In the rest of the observations, we are unable to model them with any distribution. In two sources, namely, BL Lacertae and S4 0954+650, the lognormal distribution is preferred over the normal distribution, which could arise from non-Gaussian perturbations from relativistic jets or linear Gaussian perturbation in the particle time scale leading to such flux distributions. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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13 pages, 450 KiB

Open AccessArticle

A Machine Learning Approach for Predicting Black Hole Mass in Blazars Using Broadband Emission Model Parameters

by Krishna Kumar Singh, Anilkumar Tolamatti, Sandeep Godiyal, Atul Pathania and Kuldeep Kumar Yadav

Universe 2022, 8(10), 539; https://doi.org/10.3390/universe8100539 - 18 Oct 2022

Cited by 2 | Viewed by 1156

Abstract

Blazars are observed to emit non-thermal radiation across the entire electromagnetic spectrum from the radio to the very-high-energy

γ

-ray region. The broadband radiation measured from a blazar is dominated by emission from a relativistic plasma jet which is assumed to be powered [...] Read more.

Blazars are observed to emit non-thermal radiation across the entire electromagnetic spectrum from the radio to the very-high-energy

γ

-ray region. The broadband radiation measured from a blazar is dominated by emission from a relativistic plasma jet which is assumed to be powered by a spinning supermassive black hole situated in the central region of the host galaxy. The formation of jets, their mode of energy transport, actual power budget, and connection with the central black hole are among the most fundamental open problems in blazar research. However, the observed broadband spectral energy distribution from blazars is generally explained by a simple one-zone leptonic emission model. The model parameters place constraints on the contributions from the magnetic field, radiation field, and kinetic power of particles to the emission region in the jet. This in turn constrains the minimum power transported by the jet from the central engine. In this work, we explore the potential of machine learning frameworks including linear regression, support vector machine, adaptive boosting, bagging, gradient boosting, and random forests for the estimation of the mass of the supermassive black hole at the center of the host galaxy of blazars using the best-fit emission model parameters derived from the broadband spectral energy distribution modeling in the literature. Our study suggests that the support vector machine, adaptive boosting, bagging, and random forest algorithms can predict black hole masses with reasonably good accuracy. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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16 pages, 748 KiB

Open AccessArticle

Long-Term Monitoring of Blazar PKS 0208-512: A Change of γ-Ray Baseline Activity from EGRET to Fermi Era

by Krishna Mohana Ammenadka, Debbijoy Bhattacharya, Subir Bhattacharyya, Nilay Bhatt and Chelliah Subramonian Stalin

Universe 2022, 8(10), 534; https://doi.org/10.3390/universe8100534 - 17 Oct 2022

Cited by 1 | Viewed by 1103

Abstract

The blazar PKS 0208-512 was in the lowest

γ

-ray brightness state during the initial 10 years of observations with the Fermi Gamma-ray Space Telescope (Fermi), which was an order of magnitude lower than its flux state during the EGRET era [...] Read more.

The blazar PKS 0208-512 was in the lowest

γ

-ray brightness state during the initial 10 years of observations with the Fermi Gamma-ray Space Telescope (Fermi), which was an order of magnitude lower than its flux state during the EGRET era (1991–2000). The weekly averaged maximum

γ

-ray flux of this source during the first 10 years of Fermi observation is nearly a factor of 3 lower than the highest flux observed by EGRET in a single epoch. During the period 2018–2020, the source showed a large

γ

-ray flare, with the average brightness similar to the period 1991–2000. We observed the source with AstroSat, during its low and high activity states, respectively. We carried out broad-band spectral energy distribution (SED) modeling of the source using a one-zone leptonic emission model during its various brightness states. From the SED modeling, we found that there was an inefficient conversion from the bulk energy to the particle energy during the long-term low-activity states as compared to the high flux state during the EGRET era and the later part of Fermi observation. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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11 pages, 345 KiB

Open AccessArticle

The Orbital and Epicyclic Frequencies in Axially Symmetric and Stationary Spacetime

by Bobur Turimov and Ozodbek Rahimov

Universe 2022, 8(10), 507; https://doi.org/10.3390/universe8100507 - 26 Sep 2022

Cited by 5 | Viewed by 1115

Abstract

Motivated by observational evidence of the electromagnetic signal from the X-ray binary system known as quasi-periodic oscillations in the light curves of astrophysical black holes or neutron stars, we examined the general relativity and alternative theory of gravity in the strong gravity regime. [...] Read more.

Motivated by observational evidence of the electromagnetic signal from the X-ray binary system known as quasi-periodic oscillations in the light curves of astrophysical black holes or neutron stars, we examined the general relativity and alternative theory of gravity in the strong gravity regime. The orbital and epicyclic motion of test particles in general axially symmetric spacetime was investigated. We provide a general description to derive the exact analytical expressions for the fundamental frequencies, namely, Keplerian epicyclic (radial and vertical) frequencies of test particles in an arbitrary axisymmetric and stationary spacetime. The detailed derivation of the expressions for the orbital and epicyclic frequencies of test particles orbiting around the Kerr–Newman-NUT black hole is also shown. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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13 pages, 1816 KiB

Open AccessArticle

The Classification of Blazar Candidates of Uncertain Types

by Jun-Hui Fan, Ke-Yin Chen, Hu-Bing Xiao, Wen-Xin Yang, Jing-Chao Liang, Guo-Hai Chen, Jiang-He Yang, Yu-Hai Yuan and De-Xiang Wu

Universe 2022, 8(8), 436; https://doi.org/10.3390/universe8080436 - 22 Aug 2022

Cited by 6 | Viewed by 1252

Abstract

In this work, the support vector machine (SVM) method is adopted to separate BL Lacertae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) in the plots of the photon spectrum index against the photon flux,

α_{ph} \sim \log F

, those [...] Read more.

In this work, the support vector machine (SVM) method is adopted to separate BL Lacertae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) in the plots of the photon spectrum index against the photon flux,

α_{ph} \sim \log F

, those of the photon spectrum index against the variability index,

α_{ph} \sim \log V I

and those of the variability index against the photon flux,

\log V I \sim \log F

. Then, we used the dividing lines to distinguish BL Lacs from FSRQs in the blazar candidates of uncertain types from the Fermi/LAT catalogue. Our main conclusions are: 1. We separate BL Lacs and FSRQs by

α_{ph} = - 0.123 \log F + 1.170

in the

α_{ph} \sim \log F

plot,

α_{ph} = - 0.161 \log V I + 2.594

in the

α_{ph} \sim \log V I

plot and

\log V I = 0.792 \log F + 9.203

in the

\log V I \sim \log F

plot. 2. We obtain 932 BL Lac candidates and possible BL Lac candidates, and 585 FSRQ candidates and possible FSRQ candidates. 3. Discussion is given regarding comparisons with the literature. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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13 pages, 500 KiB

Open AccessArticle

Spectral and Timing Properties of H 1743-322 in the “Faint” 2005 Normal Outburst

by Aijun Dong, Chang Liu, Qijun Zhi, Ziyi You, Qibin Sun and Bowen Du

Universe 2022, 8(5), 273; https://doi.org/10.3390/universe8050273 - 06 May 2022

Cited by 1 | Viewed by 1744

Abstract

H 1743-322 is a well-known black hole X-ray binary (BH XRBs) that has been observed in several outbursts over the past. In this work, we have performed the spectral and timing analysis of H 1743-322 during the “faint” 2005 outburst for the first [...] Read more.

H 1743-322 is a well-known black hole X-ray binary (BH XRBs) that has been observed in several outbursts over the past. In this work, we have performed the spectral and timing analysis of H 1743-322 during the “faint” 2005 outburst for the first time with the RXTE/PCA data. In this outburst, the spectral and timing parameters (e.g.,

T_{in}

,

Γ

,

R_{in}

,

r m s

and QPOs, etc.) presented an obvious change and a q-like pattern was found in the Hardness Intensity Diagram (HID), which often named as the hysteresis effect of BH XRBs. The radius of the innermost stable circular orbit was constrained as

R_{ISCO}

∼3.50

R_{g}

, which predicts that H 1743-322 is a lower-spin black hole. We further explored the correlation between timing and spectral properties. The relation of photon index

Γ

and X-ray flux,

F_{3 - 25 keV}

, presented a transition between negative and positive correlation when the X-ray luminosity,

L_{3 - 25 keV}

, is above and below a critical X-ray luminosity,

L_{X, crit} ≃ 2.55 \times 10^{- 3}

L_{Edd}

, which can be well explained by the Shakura-Sunyaev disk–corona model (SSD-corona) and advection-dominated accretion flow (ADAF). We also found the tight linear, negative correlation between photon index

Γ

and the total fractional

r m s

. Since the amount of soft photons from the accretion disk seems invariable, an increase of the number of soft photons will dilute the variability from the harder photons. Therefore, the softer the X-ray spectra will result in the smaller total fractional

r m s

. The above results suggested that the 2005 outburst of H 1743-322 was a normal outburst and H 1743-322 represented similar properties with other black hole X-ray binaries. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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Review

Jump to: Research

8 pages, 250 KiB

Open AccessReview

Thermal Radiation from Compact Objects in Curved Space-Time

by Abhas Mitra and Krishna Kumar Singh

Universe 2022, 8(10), 504; https://doi.org/10.3390/universe8100504 - 26 Sep 2022

Cited by 1 | Viewed by 949

Abstract

We highlight here the fact that the distantly observed luminosity of a spherically symmetric compact star radiating thermal radiation isotropically is higher by a factor of

{(1 + z_{b})}^{2}

compared to the corresponding flat space-time case, where

z_{b}

[...] Read more.

We highlight here the fact that the distantly observed luminosity of a spherically symmetric compact star radiating thermal radiation isotropically is higher by a factor of

{(1 + z_{b})}^{2}

compared to the corresponding flat space-time case, where

z_{b}

is the surface gravitational redshift of the compact star. In particular, we emphasize that if the thermal radiation is indeed emitted isotropically along the respective normal directions at each point, this factor of increment

{(1 + z_{b})}^{2}

remains unchanged even if the compact object would lie within its photon sphere. Since a canonical neutron star has

z_{b} \approx 0.1

, the actual X-ray luminosity from the neutron star surface could be

\sim 20 %

higher than what would be interpreted by ignoring the general relativistic effects described here. For a static compact object, supported by only isotropic pressure, compactness is limited by the Buchdahl limit

z_{b} < 2.0

. However, for compact objects supported by anisotropic pressure,

z_{b}

could be even higher (

z_{b} < 5.211

). In addition, in principle, there could be ultra-compact objects having

z_{b} ≫ 1

. Accordingly, the general relativistic effects described here might be quite important for studies of thermal radiation from some ultra-compact objects. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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