J/ApJS/255/7ivo://CDS.VizieR/J/ApJS/255/7doi:10.26093/cds/vizier.22550007CDSRicci C.Loewenstein M.Kara E.Remillard R.Trakhtenbrot B.,Arcavi I.Gendreau K.C.Arzoumanian Z.Fabian A.C.Li R.Ho L.C.,Macleod C.L.Cackett E.Altamirano D.Gandhi P.Kosec P.Pasham D.,Steiner J.Chan C.-H.2021-12-06T19:56:23Z2021-11-25T08:13:04ZCDS support team

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

cds-question@unistra.fractive-galactic-nucleix-ray-sources1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678ks) and 14 Swift/XRT (26ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior unlike any previously known AGN. The source is extremely variable both in spectral shape and flux and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst, the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT~80eV (for a 0.3-2keV luminosity of L_0.3-2_~10^41.5^erg/s) to ~200eV (for L_0.3-2_~10^44^erg/s). The spectra show evidence of ionized outflows and of a prominent feature at ~1keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.2021ApJS..255....7Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/255/7CatalogResearchIsServedByTAP VizieR generic servicerelated-toB/swift : Swift Master Catalog (HEASARC, 2004-)B/xmm : XMM-Newton Obs. Log (XMM-Newton Science Operation Center, 2012)IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)J/ApJS/129/547 : RBSC-NVSS sample. I. (Bauer+, 2000)J/MNRAS/397/1177 : Swift-XRT observations of GRBs (Evans+, 2009)J/ApJ/705/1336 : X-ray measurements of ChaMP-SDSS gal. (Constantin+, 2009)J/MNRAS/423/600 : Type-1 low-z AGN emission properties (Stern+, 2012)J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)J/A+A/588/A70 : Hard X-ray view of the soft excess in AGN (Boissay+, 2016)J/MNRAS/466/3309 : X-ray flux variability of AGN (Rani+, 2017)J/ApJ/836/99 : NuSTAR serendipitous survey: 40-month cat. (Lansbury+, 2017)J/ApJ/850/74 : Swift/BAT AGN Spectroscopic Survey. I. (Koss+, 2017)J/ApJS/233/17 : Swift/BAT AGN spectroscopic survey. V. X-ray (Ricci+, 2017)J/ApJ/854/160 : SDSS and DES long-term extreme var. QSOs (Rumbaugh+, 2018)J/ApJ/874/8 : Follow-up spec. of SDSS changing-look QSOs (Macleod+, 2019)J/ApJ/883/94 : Opt. and UV follow-up of 1ES 1927+654 (Trakhtenbrot+, 2019)J/MNRAS/498/4033 : Extreme quasar X-ray variability (Timlin+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJS/255/7https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJS/255/7http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJS/255/7https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJS/255/7https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJS/255/7http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJS/255/7GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapX-raydefaultJ/ApJS/255/7/tablea1X-ray observation logrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTelX-ray telescope (1)instr.telcharObsDate of observation, ISO 8601stime.epochnullableObsIdObservation ID on Telmeta.id;obsExpExposure timestime.duration;obs.exposureint