J/A+A/672/A167ivo://CDS.VizieR/J/A+A/672/A167doi:10.26093/cds/vizier.36720167CDSHoman D.Krumpe M.Markowitz A.Saha T.Gokus A.Partington E.,Lamer G.Malyali A.Liu Z.Rau A.Grotova I.Cackett E.M.,Buckley D.A.H.Ciroi S.Di Mille F.Gendreau K.Gromadzki M.,Krishnan S.Schramm M.Steiner J.F.2024-11-28T20:02:56Z2023-04-19T08:41:33ZCDS support team

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

cds-question@unistra.fractive-galactic-nucleix-ray-sourcesphotometryvisible-astronomyIn November 2020, a new, bright object, eRASSt J234402.9-352640, was discovered in the second all-sky survey of SRG/eROSITA. The object brightened by a factor of at least 150 in 0.2-2.0keV flux compared to an upper limit found six months previous, reaching an observed peak of 1.76^+0.03^_-0.24_x10^-11^erg/cm^2^/s. The X-ray ignition is associated with a galaxy at z=0.10, making the peak luminosity log10(L0.2-2keV/[erg/s])=44.7+/-0.1. Around the time of the rise in X-ray flux, the nucleus of the galaxy brightened by approximately 3mag. in optical photometry, after correcting for the host contribution. We present X-ray follow-up data from Swift, XMM-Newton, and NICER, which reveal a very soft spectrum as well as strong 0.2-2.0keV flux variability on multiple timescales. Optical spectra taken in the weeks after the ignition event show a blue continuum with broad, asymmetric Balmer emission lines, and high-ionisation ([OIII]4959,5007) and low-ionisation ([NII]6585, [SII]6716,6731) narrow emission lines. Following the peak in the optical light curve, the X-ray, UV, and optical photometry all show a rapid decline. The X-ray light curve shows a decrease in luminosity of ~0.45 over 33 days and the UV shows a drop of ~0.35 over the same period. eRASSt J234402.9-352640 also shows a brightening in the mid-infrared, likely powered by a dust echo of the luminous ignition. We find no evidence in Fermi-LAT gamma-ray data for jet-like emission. The event displays characteristics of a tidal disruption event (TDE) as well as of an active galactic nucleus (AGN), complicating the classification of this transient. Based on the softness of the X-ray spectrum, the presence of high-ionisation optical emission lines, and the likely infrared echo, we find that a TDE within a turned-off AGN best matches our observations.2023A&A...672A.167Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/672/A167CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/672/A167https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/672/A167http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/672/A167https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/672/A167https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/672/A167http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/672/A167GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapX-rayOpticaldefaultJ/A+A/672/A167/table4Optical photometric data for eRASSt J234402.9-352640, combining data from several instrumentsMJDObserving datedtime.epochdoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSurveyName of survey/instrument from which the entry originatesmeta.id;meta.maincharFilterName of the filter used for the observation (1)meta.id;instr.setup;instr.filtercharmagAB magnitudemagphot.magfloate_mag? 1sigma error on AB magnitudemagstat.error;phot.magfloatnullable