J/A+A/675/A44ivo://CDS.VizieR/J/A+A/675/A44doi:10.26093/cds/vizier.36750044CDSQuirola-Vasquez J.Bauer F.E.Jonker P.G.Brandt W.N.Yang G.,Levan A.J.Xue Y.Q.Eappachen D.Camacho E.Ravasio M.E.Zheng X.C.,Luo B.2024-11-06T20:05:12Z2023-06-30T09:52:00ZCDS support team

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

cds-question@unistra.frx-ray-sourcesExtragalactic fast X-ray transients (FXTs) are short flashes of X-ray photons of unknown origin that last a few minutes to hours. We extend the search for extragalactic FXTs from Quirola et al. 2022 (Paper I; based on sources in the Chandra Source Catalog 2.0, CSC2, using data taken between 2000-2014) to further Chandra archival data between 2014-2022. We extract X-ray data using a method similar to that employed by CSC2 and apply identical search criteria as in Paper I (Quirola et al., 2022A&A...663A.168Q). We report the detection of eight FXT candidates, with peak 0.3-10keV fluxes between 1*10^-13^ to 1*10^-11^erg/cm^2^/s and T90 values from 0.3 to 12.1ks. This sample of FXTs has likely redshifts between 0.7 to 1.8. Three FXT candidates exhibit light curves with a plateau (~1-3ks duration) followed by a power-law decay and X-ray spectral softening, similar to what was observed for a few previously reported FXTs in Paper I. In light of the new, expanded source lists (eight FXTs with known redshifts from Paper I and this work), we update the event sky rates derived in Paper I, finding 36.9^+9:7^_-8.3_deg^2^*yr^-1^ for the extragalactic samples for a limiting flux of >~1*10^-13^erg/cm^2^/s, calculate the first FXT X-ray luminosity function, and compare the volumetric density rate between FXTs and other transient classes. Our latest Chandra-detected extragalactic FXT candidates boost the total Chandra sample by 50%, and appear to have a similar diversity of possible progenitors.2023A&A...675A..44Qhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/675/A44CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/675/A44https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/675/A44http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/675/A44https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/675/A44https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/675/A44http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/675/A44GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/675/A44/table3 (Properties of the extragalactic FXT candidates detected and/or discussed in this work, ordered by date.)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/675/A44/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/675/A44/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/675/A44/table3?GETtext/xml+votable180.050000true233.7349623.468490.0055555555555555566/948 1679 8673 10312 17761 35935 46424https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/675/A44?format=asciiX-raydefaultJ/A+A/675/A44/table3Properties of the extragalactic FXT candidates detected and/or discussed in this work, ordered by date.recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFXT[15/22] Shorthand identifier (FXT NN) used throughout this workmeta.idintXRTX-ray transient identifier (XRT date), plus previous name when availablemeta.id;meta.maincharn_XRT[+] Note on XRT (1)meta.notecharObsIDChandra observation IDmeta.id;obsintTexpChandra observation exposure timekstime.duration;obsfloatDateChandra observation datetime.epoch;obschare_T90Error on T90 (lower limit)ksstat.errorfloatE_T90Error on T90 (upper limit)ksstat.error;stat.maxfloatT90T_90_ duration, which measures the time over which the source emits the central 90% (i.e., from % to 95%) of its total measured counts, in units of kskstime.duration;arith.ratiofloatRAJ2000Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainOffAxisOff-axis angle of the FXT candidates, with respect to the Chandra aimpointarcmininstr.offsetfloatePosEstimated 2{sigma} X-ray positional uncertainty (see Sect. 2.5).arcsecstat.error;posfloatHRHardness ratio (2)phot.flux;arith.ratiofloate_HRHardness ratio 1{sigma} uncertaintystat.errorfloatS/NApproximate signal-to-noise ratio (S/N)stat.snrfloat