J/ApJ/937/8ivo://CDS.VizieR/J/ApJ/937/8doi:10.26093/cds/vizier.19370008CDSYao Y.Lu W.Guolo M.Pasham D.R.Gezari S.Gilfanov M.,Gendreau K.C.Harrison F.Cenko S.B.Kulkarni S.R.Miller J.M.,Walton D.J.Garcia J.A.van Velzen S.Alexander K.D.,Miller-Jones J.C.A.Nicholl M.Hammerstein E.Medvedev P.Stern D.,Ravi V.Sunyaev R.Bloom J.S.Graham M.J.Kool E.C.Mahabal A.A.,Masci F.J.Purdum J.Rusholme B.Sharma Y.Smith R.Sollerman J.2024-11-06T20:27:42Z2024-08-30T14:46:20ZCDS support team

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

cds-question@unistra.frx-ray-sourcesultraviolet-photometryvisible-astronomyWe present X-ray, UV, optical, and radio observations of the nearby (~78Mpc) tidal disruption event AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy hosting a ~10^7^M_{sun}_ black hole (MBH inferred from host galaxy scaling relations). High-cadence Swift and Neutron Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first undergoes a gradual soft -> hard transition and then suddenly turns soft again within 3 days at {delta}t~272d during which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation ({delta}t=264d, harder state), we observe a prominent nonthermal component up to 30keV and an extremely broad emission line in the iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of 6.0_-3.8_^+10.4^%L_Edd_ when the X-ray spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical luminosity stays relatively constant, and the optical spectra are featureless. We propose the following interpretations: (i) the soft -> hard transition may be caused by the gradual formation of a magnetically dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical depth (~a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger column density-the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the thermal-viscous instability in the inner accretion flow, leading to a much thinner disk.2022ApJ...937....8Yhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/937/8CatalogResearchIsServedByTAP VizieR generic servicerelated-toB/xmm : XMM-Newton Observation Log (XMM-Newton Science Operation Center, 2012-)III/218 : ELODIE archive (Prugniel+, 2001)II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)II/328 : AllWISE Data Release (Cutri+ 2013)V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009)J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)J/A+A/593/A68 : PTF12os & iPTF13bvn spectra & light curves (Fremling+, 2016)J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)J/ApJS/222/15 : WATCHDOG: all-sky database of Gal. BHXBs (Tetarenko+, 2016)J/ApJ/844/46 : Phot. of the transient event iPTF16fnl (Blagorodnova+, 2017)J/A+A/631/A147 : Transient processing & analysis using AMPEL (Nordin+, 2019)J/ApJ/872/198 : UV-Opt LC of flare AT2018zr (van Velzen+, 2019)J/ApJ/886/152 : ZTF early observations of Type Ia SNe. I. LCs (Yao+, 2019)J/ApJ/900/46 : UV, optical and IR LC of supernova SN2019dge (Yao+, 2020)J/ApJ/909/102 : SDSSJ143359.16+400636.0 nucleus LRIS sp. (Brightman+, 2021)J/ApJS/266/9 : Young Supernova Experiment (YSE) DR1 (Aleo+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/937/8https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/937/8http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/937/8https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/937/8https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/937/8http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/937/8GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapX-rayUVOpticaldefaultJ/ApJ/937/8/table8UV and optical photometry of AT2021ehbrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD[59250.16/59679.14] Modified Julian Date (UT)dtime.epochdoubleFiltFilter identifier (uvw1,uvw2,uvm2,UBV,ugri)meta.id;instr.filtercharFlux[-23.21/720.7] Flux in FiltuJyphot.flux.densitydoublee_Flux[1.85/181.1] Uncertainty in FluxuJystat.error;phot.fluxdoubleInstInstrument identifier (1)meta.id;instrchar