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Title: Revisiting Optical Tidal Disruption Events with iPTF16axa

We report the discovery by the intermediate Palomar Transient Factory (iPTF) of a candidate tidal disruption event (TDE) iPTF16axa at z = 0.108 and present its broadband photometric and spectroscopic evolution from three months of follow-up observations with ground-based telescopes and Swift. The light curve is well fitted with a t -5/3 decay, and we constrain the rise time to peak to be <49 rest-frame days after disruption, which is roughly consistent with the fallback timescale expected for the ~5 × 10 6 M black hole inferred from the stellar velocity dispersion of the host galaxy. The UV and optical spectral energy distribution is well described by a constant blackbody temperature of T ~ 3 × 10 4 K over the monitoring period, with an observed peak luminosity of 1.1 × 10 44 erg s -1. The optical spectra are characterized by a strong blue continuum and broad He ii and Hα lines, which are characteristic of TDEs. We compare the photometric and spectroscopic signatures of iPTF16axa with 11 TDE candidates in the literature with well-sampled optical light curves. Based on a single-temperature fit to the optical and near-UV photometry, most of these TDE candidates have peak luminosities confined between log(L [erg s -1]) = 43.4–44.4, with constant temperatures of a few ×104 K during their power-law declines, implying blackbody radii on the order of 10 times the tidal disruption radius, that decrease monotonically with time. For TDE candidates with hydrogen and helium emission, the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas, where nebular arguments break down. In conclusion, we find no correlation between the peak luminosity and the black hole mass, contrary to the expectations for TDEs to have $$\dot{M}\propto {M}_{\mathrm{BH}}^{-1/2}$$.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [2] ; ORCiD logo [4] ; ORCiD logo [3] ;  [5] ; ORCiD logo [6] ; ORCiD logo [6] ; ORCiD logo [7] ; ORCiD logo [3] ; ORCiD logo [8] ; ORCiD logo [9] ; ORCiD logo [10] ; ORCiD logo [11]
  1. Univ. of Maryland, College Park, MD (United States). Dept. of Astronomy
  2. Univ. of Maryland, College Park, MD (United States). Dept. of Astronomy; Univ. of Maryland, College Park, MD (United States). Joint Space-Science Inst.
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States). Dept. of Astronomy
  4. Univ. of Maryland, College Park, MD (United States). Joint Space-Science Inst.; NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  5. Hebrew Univ. of Jerusalem (Israel). Racah Inst. of Physics
  6. Univ. of California, Santa Barbara, CA (United States). Dept. of Physics; Las Cumbres Observatory, Goleta, CA (United States)
  7. California Inst. of Technology (CalTech), Pasadena, CA (United States). Caltech Optical Observatories, Cahill Center for Astronomy and Astrophysics; California Inst. of Technology (CalTech), Pasadena, CA (United States). Infrared Processing and Analysis Center
  8. Stockholm Univ. (Sweden). Oskar Klein Center, Dept. of Astronomy
  9. California Inst. of Technology (CalTech), Pasadena, CA (United States). Dept. of Astronomy; Univ. of Washington, Seattle, WA (United States). eScience Inst. and Astronomy Dept.
  10. Univ. of California, Berkeley, CA (United States). Dept. of Astronomy; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  11. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-17-27705
Journal ID: ISSN 1538-4357; TRN: US1800380
Grant/Contract Number:
AC52-06NA25396; AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 842; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; Astronomy and Astrophysics; accretion; accretion disks; black hole physics; galaxies: nuclei; ultraviolet general
OSTI Identifier:
1412865
Alternate Identifier(s):
OSTI ID: 1437960