J/MNRAS/498/4033 Extreme quasar X-ray variability (Timlin+, 2020)
The frequency of extreme X-ray variability for radio-quiet quasars.
Timlin J.D., Brandt W.N., Zhu S., Liu H., Luo B, Ni Q.
<Mon. Not. R. Astron. Soc. 498, 4033-4050 (2020)>
=2020MNRAS.498.4033T 2020MNRAS.498.4033T (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; QSOs ; X-ray sources
Keywords: galaxies: active - quasars: general - X-rays: galaxies -
X-rays: general
Abstract:
We analyze 1598 serendipitous Chandra X-ray observations of 462
radio-quiet quasars to constrain the frequency of extreme amplitude
X-ray variability that is intrinsic to the quasar corona and innermost
accretion flow. The quasars in this investigation are all
spectroscopically confirmed, optically bright (mi≤20.2), and
contain no identifiable broad absorption lines in their
optical/ultraviolet spectra. This sample includes quasars spanning
z∼0.1-4 and probes X-ray variability on timescales of up to ∼12
rest-frame years. Variability amplitudes are computed between every
epoch of observation for each quasar and are analyzed as a function of
timescale and luminosity. The tail-heavy distributions of variability
amplitudes at all timescales indicate that extreme X-ray variations
are driven by an additional physical mechanism and not just typical
random fluctuations of the coronal emission. Similarly, extreme X-ray
variations of low-luminosity quasars seem to be driven by an
additional physical mechanism, whereas high-luminosity quasars seem
more consistent with random fluctuations. The amplitude at which an
X-ray variability event can be considered extreme is quantified for
different timescales and luminosities. Extreme X-ray variations occur
more frequently at long timescales ({DELTA}t≥300-days) than at
shorter timescales, and in low-luminosity quasars compared to
high-luminosity quasars over a similar timescale. A binomial analysis
indicates that extreme intrinsic X-ray variations are rare, with a
maximum occurrence rate of <2.4% of observations. Finally, we present
X-ray variability and basic optical emission-line properties of three
archival quasars that have been newly discovered to exhibit extreme
X-ray variability.
Description:
Serendipitous Chandra observations of SDSS quasars.
To assemble our quasar catalog, we combined the SDSS datarelease
fourteen quasar catalog (DR14Q; Paris et al., 2018A&A...613A..51P 2018A&A...613A..51P,
Cat. VII/286) and the large quasar catalog from Richards et al. (2015,
Cat. J/ApJS/219/39) which compiled other spectroscopically-confirmed
quasars that overlap the SDSS imaging footprint.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
appena.dat 461 1972 Quasars with duplicate Chandra observations
(table A1)
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See also:
VII/286 : SDSS quasar catalog, fourteenth data release (Paris+, 2018)
J/ApJS/219/39 : QSOs selection from SDSS and WISE (Richards+, 2015)
Byte-by-byte Description of file: appena.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Object Name (HHMMSS.ssss+DDMMSS.ssss)
25- 43 F19.15 deg RAdeg Right Ascension (J2000)
45- 66 F22.18 deg DEdeg Declination (J2000)
68- 86 F19.17 --- z Redshift (1)
88-105 F18.15 [cm-2] logNH log Galactic column density (2)
107-111 I5 d MJD MJD of the Chandra observation
113-130 F18.15 mag imag Apparent i-band magnitude
132-151 F20.18 mag Ei Reddening in the i-band (3)
153-157 I5 --- ObsID Chandra observation ID
159-176 F18.16 arcmin Theta Chandra off-axis angle
178-197 F20.13 s Tefffull Full-band effective exposure time
199-222 E24.19 --- Pbsoft [0/1] Binomial probability of detection
(soft band)
224-247 E24.19 --- Pbhard [0/1] Binomial probability of detection
(hard band)
249-272 E24.19 --- Pbfull [0/1] Binomial probability of detection
(full band)
274-294 F21.16 ct CTFull Net counts in the full band
296-314 F19.16 ct E_CTFull One sigma upper limit on net counts
316-335 F20.17 ct e_CTFull One sigma lower limit on net counts
337-356 E20.15 cm2.s meanSRCExpf Mean exposure map pixel value of the
source region
358-377 E20.15 cm2.s meanBGExpf Mean exposure map pixel value of the
background region
379 I1 --- ChipEdge [0/1] Chip-edge flag (4)
381-398 E18.13 s Tstart Chandra start time
400 I1 --- fbrightCl [0/1]? Bright cluster flag (5)
402 I1 --- BALFlag [0/3]? BAL flag (6)
404-411 F8.4 mag iMAG Absolute magnitude (corrected to z=2)
413-430 F18.15 [10-7W/Hz] logL2500 Logarithm of the rest-frame monochromatic
2500Å luminosity (erg/s/Hz)
432-439 F8.4 [mW/m2/Hz] logF2500 Logarithm of the rest-frame monochromatic
2500Å flux density (erg/cm2/s/Hz)
441-461 F21.18 --- logR Logarithm of the radio-loudness
parameter, R
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Note (1): see Richards et al. 2015, Cat. J/ApJS/219/39;
Paris et al., 2018A&A...613A..51P 2018A&A...613A..51P, Cat. VII/286.
Note (2): see Kalberla et al., 2005A&A...440..775K 2005A&A...440..775K, Cat. VIII/76.
Note (3): from the Schlafly & Finkbeiner (2011ApJ...737..103S 2011ApJ...737..103S) dust map;
subtract imag and Ei to obtain the de-reddened i-band magnitude.
Note (4): Chip-edge flag as follows:
0 = good detection
1 = edge detection
Note (5): Bright cluster flag as follows:
0 = no cluster
1 = cluster
Note (6): BAL flag as follows:
0 = no BAL detected
1 = BAL present
2 = mini-BAL
3 = potential low-z mini-BAL
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Acknowledgements:
John Timlin, jxt811(at)psu.edu
(End) John Timlin [Penn State University], Patricia Vannier [CDS] 18-Sep-2020