J/ApJ/883/94ivo://CDS.VizieR/J/ApJ/883/94doi:10.26093/cds/vizier.18830094CDSTrakhtenbrot B.Arcavi I.MacLeod C.L.Ricci C.Kara E.Graham M.L.,Stern D.Harrison F.A.Burke J.Hiramatsu D.Hosseinzadeh G.,Howell D.A.Smartt S.J.Rest A.Prieto J.L.Shappee B.J.,Holoien T.W.-S.Bersier D.Filippenko A.V.Brink T.G.Zheng W.Li R.,Remillard R.A.Loewenstein M.2021-04-27T12:37:10Z2021-03-24T08:46:31ZCDS support team

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

cds-question@unistra.fractive-galactic-nucleivisible-astronomyspectroscopyultraviolet-photometryx-ray-sourcesWe study the sudden optical and ultraviolet (UV) brightening of 1ES1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was part of the small and peculiar class of "true Type-2" AGNs that lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appearance of a blue, featureless continuum, followed several weeks later by the appearance of broad Balmer emission lines. This timescale is generally consistent with the expected light travel time between the central engine and the broadline emission region in (persistent) broadline AGN. Hubble Space Telescope spectroscopy reveals no evidence for broad UV emission lines (e.g., CIV{lambda}1549, CIII]{lambda}1909, MgII{lambda}2798), probably owing to dust in the broadline emission region. To the best of our knowledge, this is the first case where the lag between the change in continuum and in broadline emission of a "changing look" AGN has been temporally resolved. The nature and timescales of the photometric and spectral evolution disfavor both a change in line-of-sight obscuration and a change of the overall rate of gas inflow as driving the drastic spectral transformations seen in this AGN. Although the peak luminosity and timescales are consistent with those of tidal disruption events seen in inactive galaxies, the spectral properties are not. The X-ray emission displays a markedly different behavior, with frequent flares on timescales of hours to days, and will be presented in a companion publication.2019ApJ...883...94Thttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/883/94CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/ApJ/666/757 : CIV 1549{AA} emission line in AGNs (Sulentic+, 2007)J/MNRAS/383/581 : Broad-line Balmer decrements in blue AGN (Dong+, 2008)J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)J/MNRAS/423/600 : Type-1 low-z AGN emission properties (Stern+, 2012)J/MNRAS/426/2703 : Type 1 AGN at low z. II. (Stern+, 2012)J/ApJ/793/38 : Palomar Transient Factory photometric obs. (Arcavi+, 2014)J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)J/ApJS/219/1 : Catalog of Type-1 AGNs from SDSS-DR7 (Oh+, 2015)J/ApJ/850/74 : Swift/BAT AGN Spectroscopic Survey. I. (Koss+, 2017)J/ApJ/852/72 : LFs of tidal disruption flares (van Velzen, 2018)J/ApJ/874/8 : Follow-up spec. of SDSS changing-look QSOs (Macleod+, 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/883/94https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/883/94http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/883/94https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/883/94https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/883/94http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/883/94GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapX-rayUVOpticaldefaultJ/ApJ/883/94/fig1Long-term optical light curve of 1ES1927+654recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD[56734.5/58630.6] Modified Julian Date of Observation (JD-2400000.5)dtime.epochdoublePhase[-1349.42/510.5] Rest-frame days since 2017 December 23 (MJD=58110.2)dtime.phasedoublel_mag[l] 3-sigma non-detection limit flag on magmeta.code.errorcharmag[14.8/19.5] Apparent magnitude in Filtmagphot.magfloate_mag[0.014/0.4]? Uncertainty in mag (G1)magstat.error;phot.magfloatnullableTelTelescope (ASAS-SN or ATLAS)meta.id;instr.telcharFiltFilter (g, V or c, o)meta.id;instr.filtercharq_magQuality for mag: "bad weather"meta.code.qualcharJ/ApJ/883/94/table1Log of spectroscopic observationsf_Exp[d] Flag on Exp (1)meta.codecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateDate of observation (UT) at exposure starttime.epochnullablef_Date[*c] Flag on Date (1)meta.codecharMJD[58183.5/58622.6] Modified Julian Date at exposure startdtime.epochfloatdelT[72/503] Time since ATLAS first detection of the optical flare (MJD=58110.2), in rounded rest-frame daysdtime;arith.diffintTelTelescopemeta.id;instr.telcharInstInstrumentmeta.id;instrcharu_Exp[~] Uncertainty flag on Expmeta.code.errorcharExp[300/3600] Exposure timestime.duration;obs.exposureintspInteractive plot of the spectrummeta.ref.urlcharJ/ApJ/883/94/fig2Light curve and equivalent-width evolution of 1ES 1927+654 during the flarerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD[56734.5/58630.6] Modified Julian Date of Observation (JD-2400000.5)dtime.epochdoublePhase[-1349.42/510.5] Phase in days since 2017 December 23 (MJD=58110.2)dtime.phasedoubleEW[0.014/205]? Equivalent width in Angstrom units0.1nmspect.line.eqWidthfloatnullablee_EW[0.014/27.2]? Lower uncertainty on EW0.1nmstat.error;spect.line.eqWidthfloatnullableE_EW[0.2/13.4]? Upper uncertainty on EW0.1nmstat.error;stat.maxfloatnullableLineH{alpha} or H{beta}meta.id;spect.lineFx[0.3/1298]? 0.5-10keV X-ray fluxphot.flux;em.X-raydoublenullablee_Fx[0/24]? Lower uncertainty on Fxstat.errorfloatnullableE_Fx[0.1/16.5]? Upper uncertainty on Fxstat.error;stat.maxfloatnullableTelTelescope (ASAS-SN, ATLAS, Swift-UVOT, Swift-XRT, NICER or XMM)meta.id;instr.telcharl_mag[l] 3-sigma non-detection limit flag on magmeta.code.errorcharmag[13.89/19.5]? Apparent magnitude in Filtmagphot.magfloatnullablee_mag[0.014/0.4]? Uncertainty on mag (G1)magstat.error;phot.magfloatnullableFiltFilter (g, V; c, o or U, UVM2, UVW1, UVW2)meta.id;instr.filterchar