J/A+A/593/A55 MEXSAS catalogue (Vagnetti+, 2016)
Ensemble X-ray variability of active galactic nuclei.
II. Excess variance and updated structure function.
Vagnetti F., Middei R., Antonucci M., Paolillo M., Serafinelli R.
<Astron. Astrophys. 593, A55 (2016)>
=2016A&A...593A..55V 2016A&A...593A..55V (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; QSOs ; X-ray sources
Keywords: catalogs - galaxies: active - quasars: general - X-rays: galaxies
Abstract:
Most investigations of the X-ray variability of active galactic nuclei
(AGN) have been concentrated on the detailed analyses of individual,
nearby sources. A relatively small number of studies have treated the
ensemble behaviour of the more general AGN population in wider regions
of the luminosity-redshift plane. We want to determine the ensemble
variability properties of a rich AGN sample, called Multi-Epoch XMM
Serendipitous AGN Sample (MEXSAS), extracted from the fifth release of
the XMM-Newton Serendipitous Source Catalogue (XMMSSC-DR5), with
redshift between 0.1 and 5, and X-ray luminosities in the 0.5-4.5keV
band between 1042 and 1047erg/s. We urge caution on the use of the
normalised excess variance (NXS), noting that it may lead to
underestimate variability if used improperly. We use the structure
function (SF), updating our previous analysis for a smaller sample. We
propose a correction to the NXS variability estimator, accounting for
the light curve duration in the rest frame on the basis of the
knowledge of the variability behaviour gained by SF studies. We find
an ensemble increase of the X-ray variability with the rest-frame time
lag tau, given by tau0.12. We confirm an inverse dependence on the
X-ray luminosity, approximately as L_X-0.19. We analyse the SF in
different X-ray bands, finding a dependence of the variability on the
frequency as nu-0.15, corresponding to a softer when brighter trend.
In turn, this dependence allows us to parametrically correct the
variability estimated in observer-frame bands to that in the rest
frame, resulting in a moderate shift upwards (V-correction). Ensemble
X-ray variability of AGNs is best described by the structure function.
An improper use of the normalised excess variance may lead to an
underestimate of the intrinsic variability, so that appropriate
corrections to the data or the models must be applied to prevent these
effects.
Description:
We present the catalog of the Multi-Epoch XMM Serendipitous AGN Sample
(MEXSAS), extracted from the fifth release of the XMM-Newton
Serendipitous Source Catalogue (XMMSSC-DR5) and cross-matched with the
Sloan Digital Sky Survey Quasar catalogs DR7Q and DR12Q. It contains
2700 repeatedly observed AGN, with corrected excess variance
information.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 68 2700 The MEXSAS sample
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See also:
IX/46 : XMM-Newton Serendipitous Source Cat. 3XMM-DR5 (XMM-SSC, 2016)
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
J/A+A/536/A84 : X-ray variability of AGN (Vagnetti+, 2011)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Sequential source number
6- 9 A4 --- --- [3XMM]
11- 26 A16 --- Name Source 3XMM name (JHHMMSS.s+DDMMSS)
28- 32 F5.3 --- z Redshift
34- 42 E9.3 mW/m2 <fX> Average flux, 0.5-4.5keV
44- 45 I2 --- Nep Number of observing epochs
47- 53 F7.2 d Dtrest Rest-frame time interval
55- 60 F6.3 --- NXS Normalised excess variance
62- 68 F7.3 --- NXScorr Normalised excess variance, corrected
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Acknowledgements:
Fausto Vagnetti, fausto.vagnetti(at)roma2.infn.it
References:
Rosen et al., XMMSSC-DR5 2016A&A...590A...1R 2016A&A...590A...1R, Cat. IX/46
Schneider et al., SDSS-DR7Q 2010AJ....139.2360S 2010AJ....139.2360S, Cat. VII/260
Vagnetti et al., Paper I 2011A&A...536A..84V 2011A&A...536A..84V, Cat. J/A+A/536/A84
(End) F. Vagnetti [Univ Roma Tor Vergata, Italy], P. Vannier [CDS] 03-Aug-2016