Quasar spectral variability from the<i>XMM-Newton</i>serendipitous source catalogue

Serafinelli, Roberto; Vagnetti, F.; Middei, R.

doi:10.1051/0004-6361/201629885

Cited by 24 publications

(24 citation statements)

References 48 publications

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“…-Our spectral variability estimates, that also take errors on both fluxes and spectral indices into account, do not present a dependence on the flux. -No trend with black hole mass, Eddington ratio, redshift, Xray and bolometric luminosities is found, in agreement with our previous results (Serafinelli et al, 2017).…”

Section: Discussionsupporting

confidence: 92%

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The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars

Serafinelli

Vagnetti

Chiaraluce

et al. 2017

Front. Astron. Space Sci.

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We present the second Multi-Epoch X-ray Serendipitous AGN Sample (MEXSAS2), extracted from the 6th release of the XMM Serendipitous Source Catalog (XMMSSC-DR6), cross-matched with Sloan Digital Sky Survey quasar catalogs DR7Q and DR12Q. Our sample also includes the available measurements for masses, bolometric luminosities, and Eddington ratios. Analyses of the ensemble structure function and spectral variability are presented, together with their dependences on such parameters. We confirm a decrease of the structure function with the X-ray luminosity, and find a weak dependence on the black hole mass. We introduce a new spectral variability estimator, taking errors on both fluxes and spectral indices into account. We confirm an ensemble softer when brighter trend, with no dependence of such estimator on black hole mass, Eddington ratio, redshift, X-ray and bolometric luminosity.

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Section: Discussionsupporting

confidence: 92%

“…We update the analysis of the spectral variability parameter, initially introduced by Trevese and Vagnetti (2002) and recently adapted to the X-ray band by Serafinelli et al (2017) …”

Section: Spectral Variabilitymentioning

confidence: 99%

The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars

Serafinelli

Vagnetti

Chiaraluce

et al. 2017

Front. Astron. Space Sci.

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“…For example, a positive correlation between the photon index Γ and the accretion rate in Eddington units λ Edd has been robustly determined in different classes of AGN accreting at moderate or high level (e.g., Shemmer et al 2008;Risaliti et al 2009;Brightman et al 2013Brightman et al , 2016, but see Trakhtenbrot et al 2017 for a discording view). This result, which is strengthened by the steeper-when-brighter trend consistently observed in long-term spectral variability studies of AGN (e.g., Sobolewska & Papadakis 2009) and in large samples of quasars (Serafinelli et al 2017), suggests that the photon index can be used as an indicator of the accretion rate. This is consistent with the behavior regularly observed in Galactic black holes (GBHs) during their spectral transitions between the low/hard and high/soft states (e.g., Remillard & McClintock 2006), and lends support to the unification model of black hole systems at all scales, where the different classes of AGN can be associated with different spectral states of Galactic black holes (GBHs) during their spectral evolution (e.g., Done & Gierliński 2005).…”

Section: Discussionmentioning

confidence: 74%

The soft X-ray excess: NLS1s versus BLS1s

Gliozzi

Williams

2019

Monthly Notices of the Royal Astronomical Society

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The soft X-ray excess -the excess of X-rays below 2 keV with respect to the extrapolation of the hard X-ray spectral continuum model -is a very common feature among type 1 active galactic nuclei (AGN); yet the nature of the soft X-ray excess is still poorly understood and hotly debated. To shed some light on this issue, we have measured in a model-independent way the soft excess strength in a flux-limited sample of broad-line and narrow-line Seyfert 1 galaxies (BLS1s and NLS1s) that are matched in X-ray luminosity but different in terms of the black hole mass and the accretion rate values, with NLS1s being characterized by smaller M BH and larger m values. Our analysis, in agreement with previous studies carried out with different AGN samples, indicates that: 1) a soft excess is ubiquitously detected in both BLS1s and NLS1s; 2) the strength of the soft excess is significantly larger in the NLS1 sample, compared to the BLS1 sample; 3) combining the two samples, the strength of the soft excess appears to positively correlate with the photon index as well as with the accretion rate, whereas there is no correlation with the black hole mass. Importantly, our work also reveals the lack of an anticorrelation between the soft excess strength and the luminosity of the primary X-ray component, predicted by the absorption and reflection scenarios. Our findings suggest that the soft excess is consistent with being produced by a warm Comptonization component. Larger, more complete samples of NLS1s and BLS1s are needed to confirm these conclusions.

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“…5), which is seen both in Sample II and in the obscured subsample. This difference may be explained by the superposition of a soft component varying in flux and/or slope and a constant hard re-flection component, which can result in the "softer when brighter" behavior (e.g., Sobolewska & Papadakis 2009;Gibson & Brandt 2012;Serafinelli et al 2017). Additionally, the variability of absorption may be another possible reason, since the soft band is more easily affected by N H variation than the hard band.…”

Section: Variability Of Different Energy Bandsmentioning

confidence: 99%

Deepest View of AGN X-Ray Variability with the 7 Ms Chandra Deep Field-South Survey

Zheng

Xue

Brandt

et al. 2017

ApJ

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We systematically analyze X-ray variability of active galactic nuclei (AGNs) in the 7 Ms Chandra Deep Field-South survey. On the longest timescale (≈ 17 years), we find only weak (if any) dependence of Xray variability amplitudes on energy bands or obscuration. We use four different power spectral density (PSD) models to fit the anti-correlation between normalized excess variance (σ 2 nxv ) and luminosity, and obtain a best-fit power law index β = 1.16 +0.05 −0.05 for the low-frequency part of AGN PSD. We also divide the whole light curves into 4 epochs in order to inspect the dependence of σ 2 nxv on these timescales, finding an overall increasing trend. The analysis of these shorter light curves also infers a β of ∼ 1.3 that is consistent with the above-derived β, which is larger than the frequently-assumed value of β = 1. We then investigate the evolution of σ 2 nxv . No definitive conclusion is reached due to limited source statistics but, if present, the observed trend goes in the direction of decreasing AGN variability at fixed luminosity toward large redshifts. We also search for transient events and find 6 notable candidate events with our considered criteria. Two of them may be a new type of fast transient events, one of which is reported here for the first time. We therefore estimate a rate of fast outbursts Ṅ = 1.0 +1.1 −0.7 × 10 −3 galaxy −1 yr −1 and a tidal disruption event (TDE) rate Ṅ TDE = 8.6 +8.5 −4.9 × 10 −5 galaxy −1 yr −1 assuming the other four long outbursts to be TDEs.

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Quasar spectral variability from theXMM-Newtonserendipitous source catalogue

Cited by 24 publications

References 48 publications

The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars

The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars

The soft X-ray excess: NLS1s versus BLS1s

Deepest View of AGN X-Ray Variability with the 7 Ms Chandra Deep Field-South Survey

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