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21. SEAMBHs. X. Reverberation mapping campaign compilation
ID:
ivo://CDS.VizieR/J/ApJ/877/23
Title:
SEAMBHs. X. Reverberation mapping campaign compilation
Short Name:
J/ApJ/877/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We compiled a sample of 73 active galactic nuclei (AGNs) with reverberation mapping (RM) observations from RM campaigns, including our ongoing campaign of monitoring super-Eddington accreting massive black holes (BHs). This sample covers a large range of BH mass (M_{bullet}_=10^6^-9^M_{sun}_), dimensionless accretion rates (dM/dt=10^-2.7^-10^2.7^), and 5100{AA} luminosity (L_5100_=10^42-46^erg/s), allowing us to systematically study the AGN variability and their relations with BH mass, accretion rates, and optical luminosity. We employed the damped random walk (DRW) model to delineate the optical variability of continuum at 5100{AA} and obtained damped variability timescale ({tau}_d_) and amplitude ({sigma}_d_) using a Markov Chain Monte Carlo method. We also estimated the traditional variability amplitudes (F_var_), which provide a model-independent measure and therefore are used to test the DRW results. We found that AGN variability characteristics are generally correlated with (M_{bullet}_, dM/dt, L_5100_). These correlations are smooth from sub-Eddington to super-Eddington accretion AGNs, probably implying that the AGN variability may be caused by the same physical mechanism.
22. Spectral analysis of low-mass X-ray binaries
ID:
ivo://CDS.VizieR/J/ApJ/853/150
Title:
Spectral analysis of low-mass X-ray binaries
Short Name:
J/ApJ/853/150
Date:
21 Oct 2021
Publisher:
CDS
Description:
A recent study of a small sample of X-ray binaries (XRBs) suggests a significant softening of spectra of neutron star (NS) binaries as compared to black hole (BH) binaries in the luminosity range 10^34^-10^37^erg/s. This softening is quantified as an anticorrelation between the spectral index and the 0.5-10keV X-ray luminosity. We extend the study to significantly lower luminosities (i.e., ~a few x10^30^erg/s) for a larger sample of XRBs. We find evidence for a significant anticorrelation between the spectral index and the luminosity for a group of NS binaries in the luminosity range 10^32^-10^33^erg/s. Our analysis suggests a steep slope for the correlation i.e., -2.12+/-0.63. In contrast, BH binaries do not exhibit the same behavior. We examine the possible dichotomy between NS and BH binaries in terms of a Comptonization model that assumes a feedback mechanism between an optically thin hot corona and an optically thick cool source of soft photons. We gauge the NS-BH dichotomy by comparing the extracted corona temperatures, Compton-y parameters, and the Comptonization amplification factors: the mean temperature of the NS group is found to be significantly lower than the equivalent temperature for the BH group. The extracted Compton-y parameters and the amplification factors follow the theoretically predicted relation with the spectral index.
23. Supermassive BH masses of reverberation-mapped AGNs
ID:
ivo://CDS.VizieR/J/ApJ/901/133
Title:
Supermassive BH masses of reverberation-mapped AGNs
Short Name:
J/ApJ/901/133
Date:
21 Feb 2022 08:57:26
Publisher:
CDS
Description:
Using different kinds of velocity tracers derived from the broad H{beta} profile (in the mean or rms spectrum) and the corresponding virial factors f, the central supermassive black hole masses (M_BH_) are calculated for a compiled sample of 120 reverberation-mapped (RM) active galactic nuclei (AGNs). For its subsample of RM AGNs with measured stellar velocity dispersion ({sigma}_*_), the multivariate linear regression technique is used to calibrate the mean value f, as well as the variable FWHM-based f. It is found that, whether excluding the pseudobulges or not, the M_BH_ from the H{beta} line dispersion in the mean spectrum ({sigma}_H{beta},mean_) has the smallest offset rms with respect to the M_BH_-{sigma}_*_ relation. For the total sample excluding SDSS-RM AGNs, with respect to M_BH_ from {sigma}_*_ or that from the H{beta} line dispersion in the rms spectrum ({sigma}_H{beta},rms_), it is found that we can obtain M_BH_ from the {sigma}_H{beta},mean_ with the smallest offset rms of 0.38 or 0.23dex, respectively. It implies that, with respect to the H{beta} FWHM, we prefer {sigma}_H{beta},mean_ to calculate M_BH_ from the single-epoch spectrum. Using the FWHM-based f, we can improve the M_BH_ calculation from FWHM(H{beta}) and the mean f, with a decreased offset rms from 0.52 to 0.39 dex with respect to M_BH_ from {sigma}_*_ for the subsample of 36 AGNs with {sigma}_*_. The value of 0.39dex is almost the same as that from {sigma}_H{beta},mean_ and the mean f.
24. Swift/XRT and NICER timing study of MAXI J1820+070
ID:
ivo://CDS.VizieR/J/ApJ/889/142
Title:
Swift/XRT and NICER timing study of MAXI J1820+070
Short Name:
J/ApJ/889/142
Date:
03 Dec 2021 13:13:00
Publisher:
CDS
Description:
We present a detailed timing analysis of the bright black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), during its first detected outburst lasting from 2018 March until 2019 October based on Swift/XRT window timing mode observations, corresponding UVOT data and NICER observations. The light curves clearly show four outbursts, with the source remaining in the hard state during its first outburst, while the rise of the second outburst corresponds with the transition to the soft state. A similar double outburst of GX339-4 has been observed in 2004. Here it is followed by two hard-state only outbursts. In many observations the power density spectra showed type-C quasi-periodic oscillations (QPOs) with characteristic frequencies below 1Hz, which suggests that the source stayed in a state of low effective accretion for large parts of its outburst. The absence of other types of QPOs hinders a precise determination of the state transitions, but from combining NICER and Swift/XRT data, we find that MAXI J1820+070 went from the hard-intermediate to the soft state in less than one day. The covariance ratios derived from NICER data show an increase toward lower energies, which indicate that the source should make a transition to the soft state. This transition finally took place, after MAXI J1820+070 stayed in the hard state at rather constant luminosity for about 116 days. The steepness of the increase of the covariance ratios is not correlated with the amount of rms variability and it does not show a monotonic evolution along the outburst.
25. TESS light curve of AGN NGC 4395
ID:
ivo://CDS.VizieR/J/ApJ/899/136
Title:
TESS light curve of AGN NGC 4395
Short Name:
J/ApJ/899/136
Date:
03 Dec 2021 13:06:51
Publisher:
CDS
Description:
We present optical light curves from the Transiting Exoplanet Survey Satellite (TESS) for the archetypical dwarf active galactic nucleus (AGN) in the nearby galaxy NGC 4395 hosting a ~105M{sun} supermassive black hole (SMBH). Significant variability is detected on timescales from weeks to hours before reaching the background noise level. The ~month-long, 30 minute-cadence, high-precision TESS light curve can be well fit by a simple damped random walk (DRW) model, with the damping timescale {tau}DRW constrained to be 2.3_-0.7_^+1.8^days (1{sigma}). NGC 4395 lies almost exactly on the extrapolation of the {tau }_DRW_-M_BH_ relation measured for AGNs with BH masses that are more than three orders of magnitude larger. The optical variability periodogram can be well fit by a broken power law with the high-frequency slope (-1.88{+/-}0.15) and the characteristic timescale ({tau}_br_=1/(2{pi}f_br_)=1.4_-0.5_^+1.9^days) consistent with the DRW model within 1{sigma}. This work demonstrates the power of TESS light curves in identifying low-mass accreting SMBHs with optical variability, and a potential global {tau}_DRW}_-M_BH_ relation that can be used to estimate SMBH masses with optical variability measurements.
26. The blueshift of the C IV broad emission line in QSOs
ID:
ivo://CDS.VizieR/J/AJ/157/148
Title:
The blueshift of the C IV broad emission line in QSOs
Short Name:
J/AJ/157/148
Date:
21 Oct 2021
Publisher:
CDS
Description:
For the sample from Ge et al. (2016MNRAS.462..966G) of 87 low-z Palomar-Green quasi-stellar objects (QSOs) and 130 high-z QSOs (0<z<5) with H{beta}-based single-epoch supermassive black hole masses, we perform a uniform decomposition of the C IV {lambda}1549 broad-line profile. Based on the rest frame defined by the [O III] {lambda}5007 narrow emission line, a medium-strong positive correlation is found between the C IV blueshift and the luminosity at 5100 {AA} or the Eddington ratio L_Bol_/L_Edd_. A medium-strong negative relationship is found between the C IV blueshift and C IV equivalent width. These results support the postulation where the radiation pressure may be the driver of C IV blueshift. There is a medium-strong correlation between the mass ratio of C IV-based to H{beta}-based M_BH_ and the C IV blueshift, which indicates that the bias for C IV-based M_BH_ is affected by the C IV profile.
27. The Megamaser Cosmology Project. X.
ID:
ivo://CDS.VizieR/J/ApJ/854/124
Title:
The Megamaser Cosmology Project. X.
Short Name:
J/ApJ/854/124
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high-resolution (submas) Very Long Baseline Interferometry maps of nuclear H_2_O megamasers for seven galaxies. In UGC 6093, the well-aligned systemic masers and high-velocity masers originate in an edge-on, flat disk and we determine the mass of the central supermassive black holes (SMBH) to be M_SMBH_=2.58x10^7^M_{sun}_ (+/-7%). For J1346+5228, the distribution of masers is consistent with a disk, but the faint high-velocity masers are only marginally detected, and we constrain the mass of the SMBH to be in the range (1.5-2.0)x10^7^M_{sun}_. The origin of the masers in Mrk 1210 is less clear, as the systemic and high-velocity masers are misaligned and show a disorganized velocity structure. We present one possible model in which the masers originate in a tilted, warped disk, but we do not rule out the possibility of other explanations including outflow masers. In NGC 6926, we detect a set of redshifted masers, clustered within a parsec of each other, and a single blueshifted maser about 4.4pc away, an offset that would be unusually large for a maser disk system. Nevertheless, if it is a disk system, we estimate the enclosed mass to be M_SMBH_<4.8x10^7^M_{sun}_. For NGC 5793, we detect redshifted masers spaced about 1.4pc from a clustered set of blueshifted features. The orientation of the structure supports a disk scenario as suggested by Hagiwara+ (2001ApJ...560..119H). We estimate the enclosed mass to be M_SMBH_<1.3x10^7^M_{sun}_. For NGC 2824 and J0350-0127, the masers may be associated with parsec- or subparsec-scale jets or outflows.
28. Xinglong optical spectra of UGC3223 in 4 epochs
ID:
ivo://CDS.VizieR/J/AJ/159/245
Title:
Xinglong optical spectra of UGC3223 in 4 epochs
Short Name:
J/AJ/159/245
Date:
21 Oct 2021
Publisher:
CDS
Description:
The discovery of spectral type transition of active galactic nuclei (AGNs), the so-called "changing-look" (CL) phenomenon, challenges the widely accepted AGN paradigm, not only in the orientation-based unified model, but also in the standard disk model. In past decades, only a couple of nearby repeat changing-look active galactic nuclei (CL-AGNs) have been identified. Here we report spectroscopic observations of UGC3223 over the course of 18yr, from 2001 onwards. Combining the spectrum taken in 1987 by Stirpe, we have witnessed its type transitions from 1.5 to 2.0 to 1.8 over 32yr, and captured a long-lived (at least 10 yr) thorough "turn-off" state with a spectrum typical of a Seyfert 2 galaxy. The long-term thorough turn-off state probably suggests a once-dormant and an awakening central engine in UGC3223. We argue that the (dis)appearance of the broad Balmer emission lines can be explained by the disk-wind broad-line region model given the evolution of the calculated Eddington ratio of accretion of the supermassive black hole.
29. 24yr of radio observations of V404 Cygni
ID:
ivo://CDS.VizieR/J/ApJ/874/13
Title:
24yr of radio observations of V404 Cygni
Short Name:
J/ApJ/874/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
Relativistic outflows are believed to be a common feature of black hole X-ray binaries (BHXBs) at the lowest accretion rates, when they are in their "quiescent" spectral state. However, we still lack a detailed understanding of how quiescent jet emission varies with time. Here we present 24yr of archival radio observations (from the Very Large Array and the Very Long Baseline Array) of the BHXB V404 Cygni in quiescence (totaling 150 observations from 1.4 to 22GHz). The observed flux densities follow lognormal distributions with means and standard deviations of (<logf{nu}>,{sigma}_logf{nu}_)=(-0.53,0.19) and (-0.53,0.30) at 4.9 and 8.4GHz, respectively (where f{nu} is the flux density in units of mJy). As expected, the average radio spectrum is flat with a mean and standard deviation of (<{alpha}_r_,{sigma}_{alpha}r_)=(0.02,0.65), where f{nu}{propto}{nu}^{alpha}_r_^. We find that radio flares that increase the flux density by factors of 2-4 over timescales as short as <10 minutes are commonplace, and that long-term variations (over 10-4000 day timescales) are consistent with shot-noise impulses that decay to stochastic variations on timescales <~10 days (and perhaps as short as tens of minutes to several hr). We briefly compare the variability characteristics of V404 Cygni to jetted active galactic nuclei, and we conclude with recommendations on how to account for variability when placing quiescent BHXB candidates with radio luminosities comparable to V404 Cygni (L_R_~10^28^erg/s) onto the radio/X-ray luminosity plane.

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