TY - JOUR

T1 - Double-peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event

AU - Hung, Tiara

AU - Foley, Ryan J.

AU - Ramirez-Ruiz, Enrico

AU - Dai, Jane L.

AU - Auchettl, Katie

AU - Kilpatrick, Charles D.

AU - Mockler, Brenna

AU - Brown, Jonathan S.

AU - Coulter, David A.

AU - Dimitriadis, Georgios

AU - Holoien, Thomas W-S

AU - Law-Smith, Jamie A. P.

AU - Piro, Anthony L.

AU - Rest, Armin

AU - Rojas-Bravo, Cesar

AU - Siebert, Matthew R.

PY - 2020/11/1

Y1 - 2020/11/1

N2 - We present the multiwavelength analysis of the tidal disruption event (TDE) AT 2018hyz (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 similar to 100 R-p and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out. Our analysis indicates that in AT 2018hyz, 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 less than or similar to 5% of the initial stellar mass. With these new insights from AT 2018hyz, 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.

AB - We present the multiwavelength analysis of the tidal disruption event (TDE) AT 2018hyz (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 similar to 100 R-p and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out. Our analysis indicates that in AT 2018hyz, 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 less than or similar to 5% of the initial stellar mass. With these new insights from AT 2018hyz, 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.

KW - Galaxy accretion disks

KW - Black hole physics

KW - High energy astrophysics

KW - BLACK-HOLES

KW - STARS

KW - LINES

KW - PHOTOMETRY

KW - EVOLUTION

KW - PROGRAM

KW - STREAM

KW - MASSES

KW - FLOWS

KW - POWER

U2 - 10.3847/1538-4357/abb606

DO - 10.3847/1538-4357/abb606

M3 - Journal article

VL - 903

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 31

ER -