J/ApJ/903/31 Photometry AT 2018hyz with Swift XRT, UVOT and Swope (Hung+, 2020) ================================================================================ Double-peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event. Hung T., Foley R.J., Ramirez-Ruiz E., Dai J.L., Auchettl K., Kilpatrick C.D., Mockler B., Brown J.S., Coulter D.A., Dimitriadis G., Holoien T.W.-S., Law-Smith J.A.P., Piro A.L., Rest A., Rojas-Bravo C., Siebert M.R. =2020ApJ...903...31H ================================================================================ ADC_Keywords: Supernovae; Photometry, UVBGRI; X-ray sources Keywords: Galaxy accretion disks ; Black hole physics ; High energy astrophysics Abstract: We present the multiwavelength analysis of the tidal disruption event (TDE) AT2018hyz (ASASSN-18zj). From follow-up optical spectroscopy, we detect the first unambiguous case of resolved double-peaked Balmer emission in a TDE. The distinct line profile can be well-modeled by a low eccentricity (e~0.1) accretion disk extending out to ~100Rp and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out. Our analysis indicates that in AT2018hyz, disk formation took place promptly after the most-bound debris returned to pericenter, which we estimate to be roughly tens of days before the first detection. Redistribution of angular momentum and mass transport, possibly through shocks, must occur on the observed timescale of about a month to create the large H{alpha}-emitting disk that comprises <~5% of the initial stellar mass. With these new insights from AT2018hyz, we infer that circularization is efficient in at least some, if not all optically bright, X-ray faint TDEs. In these efficiently circularized TDEs, the detection of double-peaked emission depends on the disk inclination angle and the relative strength of the disk contribution to the non-disk component, possibly explaining the diversity seen in the current sample. Description: AT2018hyz was observed by the Ultraviolet Optical Telescope (UVOT) and simultaneously by the X-ray Telescope (XRT) on board the Neil Gehrels Swift Observatory as well as the Swope telescope at the Las Campanas Observatory. Optical photometry of AT2018hyz in gri was obtained with the 1m Swope telescope from 2018 November 16 to 2019 June 16 with a 2-5day cadence. Objects: ---------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------- 10 06 59.6 +01 47 56.3 AT 2018hyz = ASASSN -18zj ---------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tablea1.dat 25 37 Swift XRT observations tablea2.dat 31 270 Photometric data of AT 2018hyz -------------------------------------------------------------------------------- See also: J/MNRAS/425/1789 : Berkeley supernova Ia program. I. (Silverman+, 2012) J/ApJS/208/20 : Nine-year WMAP point source catalogs (Bennett+, 2013) J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014) J/ApJ/793/38 : Palomar Transient Factory photometric obs. (Arcavi+, 2014) J/ApJ/795/44 : PS1 SNe Ia (0.02