J/MNRAS/498/4033ivo://CDS.VizieR/J/MNRAS/498/4033doi:10.26093/cds/vizier.74984033CDSTimlin J.D.Brandt W.N.Zhu S.Liu H.Luo BNi Q.2024-08-21T20:16:00Z2020-10-02T13:06:21ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fractive-galactic-nucleiquasarsx-ray-sourcesWe 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 (m_i_<=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.2020MNRAS.498.4033Thttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/498/4033CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVII/286 : SDSS quasar catalog, fourteenth data release (Paris+, 2018)J/ApJS/219/39 : QSOs selection from SDSS and WISE (Richards+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/498/4033https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/498/4033http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/498/4033https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/498/4033https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/498/4033http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/498/4033GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/498/4033/appena (Quasars with duplicate Chandra observations (table A1))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/498/4033/appena?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/498/4033/appena?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/498/4033/appena?GETtext/xml+votable180.050000true6.0088525-2.016979440.0055555555555555565/6814 6/32 1700 4178 4215 4361 4376 4448 4512 4548 4804 4808 4835 4838 4943 5051 5061 5069 5074 5099 5140 5306 5327 5587 5625 5648 5731 5733 5757 5795 5797-5799 5881 5927 5975 5985 5987 5999 6010 6073 6075 6077 6088 6399 6436 6448 6471 6536 6538 7178 7208 7239 7242-7243 7264 7273 7308 7345 7371 7424 7426 7606 8271 8338-8339 8526 8555 8707 8733 8921 8969 8972 9052 9147 9150 9181 9271 9343 9354 9428 9466 9468 9476 9496 9498 9764 9769 9842 9997 9999 10137 10158 10213 10306-10307 10312-10313 10378 10391 10400-10401 10442 10484 10512-10513 10515-10516 10518-10519 10527 10544 10551 10589 10601 10607 10704-10705 10721 10743 10769 10905 10911 11042 11044 11063 11080 11101 11179 11222 11252-11253 11259 11371-11372 11424-11425 11428 11434 11457 11467 11512 11608 11806 11810 11845 11904 17237 17406 17469 17492 17502 17622 17662 17688 17690 17699 17702 17741 17766-17767 17769 17772-17773 17840 17850 17860 18009 18016 18060 18071 18274 18385 18416 18762 18779 18790-18791 18795 18800 18826-18827 18894 19033 19036 19089 19097 19432 19458 19905 19935 19950 20021 22960 23185 23205 23216 25919 25950 25981 25990 26039 26186 26189 26208-26209 26215 26245 26298 26303 26313 26316 26470 26508 26555 26596 26956 26975 27073 27126-27127 27245 27247 27305 27344 27382 27428 27440 27476 27514-27515 27541 27571 27580 27718-27719 27730 27767 27773 27914 27921 27936 27944 27946 27948 28022 28045 28086 28149 28174 28184 28251 28377 28430 28448 28452 28495 28535 28555 28619-28620 28631 31332 32459 32500 36846 45044https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/498/4033?format=asciiX-raydefaultJ/MNRAS/498/4033/appenaQuasars with duplicate Chandra observations (table A1)SimbadNameSimbad column added by the CDSmeta.idcharnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameObject Name (HHMMSS.ssss+DDMMSS.ssss)meta.id;meta.maincharRAJ2000Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainzRedshift (1)src.redshiftdoublelogNHlog Galactic column density (2)log(cm**-2)phys.columnDensity;pos.galacticfloatMJDMJD of the Chandra observationdtime.epoch;obsintimagApparent i-band magnitudemagphot.mag;em.opt.IfloatEiReddening in the i-band (3)magphot.color.excessfloatObsIDChandra observation IDmeta.id;obsintThetaChandra off-axis anglearcmininstr.offsetfloatTefffullFull-band effective exposure timestime.duration;obs.exposuredoublePbsoft[0/1] Binomial probability of detection (soft band)stat.fit.goodnessfloatPbhard[0/1] Binomial probability of detection (hard band)stat.fit.goodnessfloatPbfull[0/1] Binomial probability of detection (full band)stat.fit.goodnessfloatCTFullNet counts in the full bandctphot.count;em.X-rayfloatE_CTFullOne sigma upper limit on net countsctstat.error;stat.maxfloate_CTFullOne sigma lower limit on net countsctstat.errorfloatmeanSRCExpfMean exposure map pixel value of the source regioncm**2.sstat.value;obs.field;stat.meandoublemeanBGExpfMean exposure map pixel value of the background regioncm**2.sinstr.background;obs.field;stat.meandoubleBALFlag[0/3]? BAL flag (6)meta.codeintnullableChipEdge[0/1] Chip-edge flag (4)meta.codeintTstartChandra start timestime.startdoublefbrightCl[0/1]? Bright cluster flag (5)meta.codeintnullableiMAGAbsolute magnitude (corrected to z=2)magphys.magAbsdoublelogL2500Logarithm of the rest-frame monochromatic 2500{AA} luminosity (erg/s/Hz)log(1e-07W.Hz**-1)phys.luminosityfloatlogF2500Logarithm of the rest-frame monochromatic 2500{AA} flux density (erg/cm^2^/s/Hz)log(mW.m**-2.Hz**-1)phot.fluxdoublelogRLogarithm of the radio-loudness parameter, Rphot.flux;arith.ratiofloat