An X-ray view of central engines of low-luminosity quasars (LLQSO) in the local Universe

Laha, Sibasish; Ghosh, Ritesh; Guainazzi, M.; Markowitz, A.

doi:10.1093/mnras/sty1919

Cited by 24 publications

(16 citation statements)

References 75 publications

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“…The sources hosted in high-mass galaxies likely have black hole masses comparable to those of the higher-luminosity AGNs, and their low X-ray luminosities are probably attributed to inefficient accreting. Conversely, those sources inhabiting low-mass dwarf galaxies may be lowermass black holes with typical accretion rates, similar to the low-luminosity quasars reported in Laha et al (2018). In terms of the star formation rates of host galaxies, the distributions of the four samples (i.e., 12 AGN candidates, 28 LLAGNs, 53 higher-luminosity AGNs, and 75 normal galaxies) are not significantly different from each other.…”

Section: Agn Candidates and Their Basic Propertiessupporting

confidence: 67%

Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

Ding

Brandt

Paolillo

et al. 2018

ApJ

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In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of luminosities have been identified. However, cosmologically distant low-luminosity AGN (LLAGN, L X 10 42 erg s −1 ) identification still poses a challenge due to significant contamination from host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the longest timescale (∼ 17 years) deep X-ray survey to date, we utilize an X-ray variability selection technique to search for LLAGNs that remain unidentified among the CDF-S X-ray sources. We find 13 variable sources from 110 unclassified CDF-S X-ray sources. Except for one source which could be an ultraluminous X-ray source, the variability of the remaining 12 sources is most likely due to accreting supermassive black holes. These 12 AGN candidates have low intrinsic X-ray luminosities, with a median value of 7 × 10 40 erg s −1 . They are generally not heavily obscured, with an average effective power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is independent of X-ray luminosity and is only restricted by the total number of observed net counts, confirming previous findings that X-ray variability is a near-ubiquitous property of AGNs over a wide range of luminosities. There is an anti-correlation between X-ray luminosity and variability amplitude for high-luminosity AGNs, but as the luminosity drops to 10 42 erg s −1 , the variability amplitude no longer appears dependent on the luminosity. The entire observed luminosity-variability trend can be roughly reproduced by an empirical AGN variability model based on a broken power-law power spectral density function.

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Section: Agn Candidates and Their Basic Propertiessupporting

confidence: 67%

Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

Ding

Brandt

Paolillo

et al. 2018

ApJ

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“…As would be expected from the paradigm described above, observations have revealed evidence that the accretion disk and X-ray corona are connected. First, there is a strong correlation between AGN UV/optical and X-ray luminosities, which is often parameterized as a relation between the optical-to-X-ray power-law slope parameter α OX 1 and L 2500 Å across a broad range in UV luminosity (e.g., Avni & Tananbaum 1982Kriss & Canizares 1985;Wilkes et al 1994;Vignali et al 2003;Strateva et al 2005;Steffen et al 2006;Just et al 2007;Gibson et al 2008;Green et al 2009;Lusso et al 2010;Grupe et al 2010;Jin et al 2012;Laha et al 2018;Chiaraluce et al 2018). This correlation can also be described as the dependence of L 2 keV on L 2500 Å (e.g., Tananbaum et al 1979;Avni & Tananbaum 1982Wilkes et al 1994;Strateva et al 2005;Steffen et al 2006;Just et al 2007;Lusso et al 2010;Lusso & Risaliti 2016;Chiaraluce et al 2 2018).…”

Section: Introductionmentioning

confidence: 99%

On the Observational Difference Between the Accretion Disk-Corona Connections among Super- and Sub-Eddington Accreting Active Galactic Nuclei

Liu,

Luo,

Brandt

et al. 2021

Preprint

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We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation-mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk-corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter (α OX ) and the monochromatic luminosity at 2500 Å (L 2500 Å ) for both the super-and sub-Eddington subsamples. The best-fit α OX -L 2500 Å relations are consistent overall, indicating that super-Eddington accreting AGNs are not particularly X-ray weak in general compared to sub-Eddington accreting AGNs. We find dependences of α OX on both the Eddington ratio (L Bol /L Edd ) and black hole mass (M BH ) parameters for our full sample. A multi-variate linear regression analysis yields α OX = −0.13log(L Bol /L Edd ) − 0.10logM BH − 0.69, with a scatter similar to that of the α OX -L 2500 Å relation. The hard (rest-frame > 2 keV) X-ray photon index (Γ) is strongly correlated with L Bol /L Edd for the full sample and the super-Eddington subsample, but these two parameters are not significantly correlated for the sub-Eddington subsample. A fraction of super-Eddington accreting AGNs show strong X-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) X-ray radiation to study the accretion disk-corona connections in AGNs.L 2500 Å are the monochromatic luminosities at rest-frame 2 keV and 2500 Å, respectively.

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“…See Table 1 for details and the short notation of the observation ids. The Suzaku reprocessing and spectral extraction were carried out following the steps described in Laha et al (2018) and Ghosh et al (2016). There is no pile up in the XIS spectra of the source.…”

Section: Observation and Data Reprocessingmentioning

confidence: 99%

Investigating the origin of the Fe emission lines of the Seyfert 1 galaxy Mrk 205

Laha

Ghosh

Tripathi

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We have investigated the nature and origin of the Fe K emission lines in Mrk 205 using observations with Suzaku and XMM-Newton, aiming to resolve the ambiguity between a broad emission line and multiple unresolved lines of higher ionization. We detect the presence of a narrow Fe Kα emission line along with a broad band Compton reflection hump at energies E > 10 keV. These are consistent with reflected emission of hard X-ray photons off a Compton thick material of N H 2.15 × 10 24 cm −2 . In addition we detect a partially covering ionized absorption with ionization parameter log(ξ/ erg cm s −1 ) = 1.9 +0.1 −0.5 , column density N H = (5.6 +2.0 −1.9 ) × 10 22 cm −2 and a covering factor of 0.22 +0.09 −0.06 . We detect the presence of emission arising out of ionized disk reflection contributing in the soft and the hard X-rays consistently in all the observations. We however, could not definitely ascertain the presence of a relativistically broadened Fe line in the X-ray spectra. Using relativistic reflection models, we found that the data are unable to statistically distinguish between the scenarios when the super-massive black hole is non-rotating and when it is maximally spinning. Using the disk reflection model we also find that the accretion disk of the AGN may be truncated at a distance 6R G < R < 12R G , which may suggest why there may not be any broad Fe line. The Eddington rate of the source is low (λ Edd = 0.03), which points to an inefficient accretion, possibly due to a truncated disk.

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An X-ray view of central engines of low-luminosity quasars (LLQSO) in the local Universe

Cited by 24 publications

References 75 publications

Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

On the Observational Difference Between the Accretion Disk-Corona Connections among Super- and Sub-Eddington Accreting Active Galactic Nuclei

Investigating the origin of the Fe emission lines of the Seyfert 1 galaxy Mrk 205

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