We construct an X-ray spectral model from the clumpy torus in an active galactic nucleus, designated as "XCLUMPY," utilizing the Monte Carlo simulation for Astrophysics and Cosmology framework. The ...adopted geometry of the torus is the same as that in Nenkova et al. who assume a power-law distribution of clumps in the radial direction and a normal distribution in the elevation direction. We investigate the dependence of the X-ray continuum and Fe K fluorescence line profile on the torus parameters. Our model is compared with other torus models: MYTorus model, Ikeda model, and CTorus model. As an example, we also present the results applied to the broadband X-ray spectra of the Circinus galaxy observed with XMM-Newton, Suzaku, and NuSTAR. Our model can well reproduce the data, yielding a hydrogen column density along the equatorial plane cm−2, a torus angular width degree, and a 2-10 keV luminosity . These results are discussed in comparison with the observations in other wavelengths.
Abstract
The Fermi satellite has detected ∼ 60 radio galaxies (RGs). In this study, we investigate the difference in the properties of X-ray spectra between GeV-loud RGs and GeV-quiet RGs. Our sample ...comprises 68 objects: 36 RGs detected with Fermi and 32 RGs not detected with gamma-rays. We analyzed the X-ray spectra of these 68 objects using data from the XMM-Newton, Chandra, NuSTAR, and Swift satellites. Our results show that most GeV-loud RGs do not exhibit significant absorption, while $\sim \!50\%$ of the GeV-quiet RGs exhibit significant absorption. This suggests that the jet of GeV-loud RGs is viewed from a small angle, and thus the emission is not easily blocked by the torus. Moreover, we reported that RGs with a heavy absorption are mostly in the X-ray luminosity range of 1043–1045 erg s−1; however, few RGs with lower and higher luminosity suffer from heavy absorption. This is the same trend as that of Seyfert galaxies.
The Study of X-Ray Flux Variability of M87 Imazawa, Ryo; Fukazawa, Yasushi; Takahashi, Hiromitsu
The Astrophysical journal,
10/2021, Letnik:
919, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
We searched for a short-term X-ray variability of the M87 core and jet from archival X-ray data with long exposure data taken by the Suzaku, Chandra, and NuSTAR telescopes. We found the ...intraday variability for the Suzaku data obtained in 2006, and for the Chandra core obtained in 2017. The intraday variability suggested a minute emission region about the size of the Schwarzschild radius of the M87 supermassive black hole. Suzaku could not resolve a core and HST-1; however, in 2006, HST-1 was much brighter than the core, and thus, the variability is likely due to the HST-1. Since the photon index in 2006 was 2.38, the emission was possibly synchrotron emission from the local shock region in the HST-1, indicating that the particle acceleration of TeV electrons occurred far away (∼100 pc) from the core. Assuming the fading time to be equal to the synchrotron cooling time, the magnetic field is constrained to be
B
∼ 1.94
δ
1/3
mG. Moreover, the photon index of the core in 2017 was approximately 1.96; thus, the possible emission was from the radiative inefficiency accretion flow of the core or inverse Compton scattering in the jet. Intraday time variability prefers the latter possibility.
Abstract
In this study, we systematically studied the X-ray to GeV gamma-ray spectra of 61 Fermi Large Area Telescope detected radio galaxies. We found an anticorrelation between peak frequency and ...peak luminosity in the high-energy spectral component of radio galaxies, similar to blazars. With this sample, we also constructed a gamma-ray luminosity function (GLF) of gamma-ray-loud radio galaxies. We found that blazar-like GLF shapes can reproduce their redshift and luminosity distribution, but the log
N
–log
S
relation prefers models with more low-
z
radio galaxies. Utilizing our latest GLF, the contribution of radio galaxies to the extragalactic gamma-ray background is found to be 1%–10%. We further investigated the nature of gamma-ray-loud radio galaxies. Compared to radio or X-ray flux-limited radio galaxy samples, the gamma-ray-selected sample tends to lack high radio power galaxies like FR II radio galaxies. We also found that only ∼10% of radio galaxies are GeV gamma-ray loud. Radio galaxies may contribute to the cosmic MeV gamma-ray background comparable to blazars if gamma-ray-quiet radio galaxies have X-ray to gamma-ray spectra like Cen A, with a small gamma-ray-to-X-ray flux ratio.
Abstract
IGR J00370+6122 is a high-mass X-ray binary with a B1 Ib primary star and a companion suggested to be a neutron star because of the detection of a 346 s pulsation in a one-off 4 ks ...observation. To better understand the nature of the compact companion, the present work performs timing and spectral studies of the X-ray data of this object, taken with XMM-Newton, Swift, Suzaku, RXTE, and INTEGRAL. In the XMM-Newton data, a sign of coherent 674 s pulsation was detected, for which the previous 346 s period may be the second harmonic. The spectra exhibited the “harder when brighter” trend in the 1–10 keV range, and a flat continuum without clear cutoff in the 10–80 keV range. These properties are both similar to those observed from several low-luminosity accreting pulsars, including X Persei in particular. Thus, the compact object in IGR J00370+6122 is considered to be a magnetized neutron star with a rather low luminosity. The orbital period was refined to 15.6649 ± 0.0014 d. Along the orbit, the luminosity changes by three orders of magnitude, involving a sudden drop from ∼4 × 1033 to ∼1 × 1032 erg s−1 at an orbital phase of 0.3 (and probably vice verse at 0.95). Although these phenomena cannot be explained by simple Hoyle–Lyttleton accretion from the primary’s stellar winds, they can be explained when incorporating the propeller effect with a strong dipole magnetic field of ∼5 × 1013 G. Therefore, the neutron star in IGR J00370+6122 may have a stronger magnetic field compared to ordinary X-ray pulsars.
Abstract GRS 1734-292 is a radio-quiet galaxy, exhibiting neither intense starburst nor jet activities. However, Fermi-LAT detected this object in the GeV band. The origin of nonthermal activity in ...this Seyfert galaxy is an intriguing question. We report Atacama Large Millimeter/submillimeter Array observations of GRS 1734-292 at frequencies of 97.5, 145, and 225 GHz. These observations confirmed the millimeter excess within the central ⪅100 pc region and its time variability based on two separate observations conducted 4 days apart. The timescale of variability aligns with the light-crossing time for a compact source smaller than <100 Schwarzschild radius. If we take into account the power-law synchrotron emission originating from the corona (i.e., the hot plasma located above the accretion disk), the millimeter spectrum indicates the coronal magnetic field of ≈10 G and the size of ≈10 Schwarzschild radius. An alternative explanation for this millimeter emission could be synchrotron and free–free emission from disk winds (i.e., fast wide-opening angle outflows from the disk) with the size of ≈10 pc, although it may be difficult to explain the fast variability. Future millimeter observations with higher resolution (<0.″01) will enable the differentiation between these two scenarios. Such observations will provide insights into the acceleration sites of high-energy particles at the core of active galactic nuclei.
We analyzed the spectral shape of the Compton shoulder around the neutral Fe-K line of the Compton-thick type II Seyfert nucleus of the Circinus galaxy. The characteristics of this Compton shoulder ...with respect to the reflected continuum and Fe-K line core intensity are powerful diagnostics tools for analyzing the structure of the molecular tori, which obscures the central engine. We applied our Monte-Carlo-based X-ray reflection spectral model to the Chandra High Energy Transmission Grating data and successfully constrained the various spectral parameters independently, using only the spectral data only around the Fe-K emission line. The obtained column density and inclination angle are consistent with previous observations and the Compton-thick type II Seyfert picture. In addition, we determined the metal abundance of the molecular torus for the case of the smooth and clumpy torus to be and 1.74 0.16 solar abundance, respectively. Such slightly over-solar abundance can be useful information for discussing the star formation rate in the molecular tori of active galactic nuclei.
Abstract
“Changing-look active galactic nuclei” (CLAGNs) are known to change their apparent types between types 1 and 2, usually accompanied by a drastic change in their luminosity on timescales of ...years. However, it is still unclear whether materials in broad-line regions (BLRs) in CLAGNs appear and disappear during the type-transition or remain at the same location while the line production is simply activated or deactivated. Here we present our X-ray–optical monitoring results of a CLAGN, NGC 3516, by Suzaku, Swift, and ground telescopes, with our primary focus on the narrow Fe–K
α
emission line, which is an effective probe of the BLR materials. We detected significant variations of the narrow Fe–K
α
line on a timescale of tens of days during the type-2 (faint) phase in 2013–2014, and conducted “narrow Fe–K
α
reverberation mapping,” comparing its flux variation with those of the X-ray continuum from a corona and
B
-band continuum from an accretion disk. We derived, as a result, a time lag of
10.1
−
5.6
+
5.8
days (1
σ
errors) for the Fe–K
α
line behind the continuum, which is consistent with the location of the BLR determined in optical spectroscopic reverberation mapping during the type-1 (bright) phase. This finding shows that the BLR materials remained at the same location without emitting optical broad lines during the type-2 phase. Considering the drastic decrease of the radiation during the type-transition, our result is possibly inconsistent with the hotly discussed formation models of the BLR, which propose that the radiative pressure from an accretion disk should be the main driving force.
ABSTRACT We have performed systematic studies of narrow Fe-K line (6.4 keV) flux variability and Ni-K line intensity for Seyfert galaxies, using Suzaku and XMM-Newton archival data. Significant Fe-K ...line variability of several tens of percent was detected for a pair of observations separated by 1000-2000 days (Cen A, IC 4329 A, NGC 3516, and NGC 4151) and 158 days (NGC 3516). These timescales are larger by a factor of 10-100 than the inner radius of the torus, consistent with the view that X-ray reflection by a torus is a main origin for a narrow Fe-K line. The Ni-K line was detected with a >2 level for the Circinus galaxy, Cen A, MRK 3, NGC 4388, and NGC 4151. A mean and variance of the Ni-K to Fe-K line intensity ratios are 0.066 and 0.026, respectively. Comparing this with the Monte-Carlo simulation of reflection, the Ni to Fe abundance ratio is 1.9 0.8 solar. We discuss the results and the possibility of Ni abundance enhancement.
Abstract
We report on the variations of the physical parameters of the jet observed in the blazar Mrk 421, and discuss the origin of X-ray flares in the jet, based on analysis of several spectral ...energy distributions (SEDs). The SEDs are modeled using the one-zone synchrotron self-Compton model, its parameters determined using a Markov chain Monte Carlo method. The lack of data at TeV energies means many of the parameters cannot be uniquely determined and are correlated. These are studied in detail. We find that the optimal solution can be uniquely determined only when we apply a constraint to one of four parameters: the magnetic field (B), the Doppler factor, the size of the emitting region, and the normalization factor of the electron energy distribution. We used 31 sets of SEDs from 2009 to 2014 with optical–UV data observed with UVOT/Swift and the Kanata telescope, X-ray data with XRT/Swift, and γ-ray data with the Fermi Large Area Telescope. The result of our SED analysis suggests that, in the X-ray faint state, the emission occurs in a relatively small area (∼1016 cm) with a relatively strong magnetic field (B ∼ 10−1 G). The X-ray bright state shows a tendency opposite to that of the faint state, that is, a large emitting area (∼1018 cm), probably downstream of the jet, and a weak magnetic field (B ∼ 10−3 G). The high X-ray flux was due to an increase in the maximum energy of electrons. On the other hand, the presence of two kinds of emitting areas implies that the one-zone model is unsuitable for reproducing at least part of the observed SEDs.
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