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Revisiting Optical Tidal Disruption Events with iPTF16axa

Hung, T. and Gezari, S. and Blagorodnova, N. and Roth, N. and Cenko, S. B. and Kulkarni, S. R. and Horesh, A. and Arcavi, I. and McCully, C. and Yan, Lin and Lunnan, R. and Fremling, C. and Cao, Y. and Nugent, P. E. and Wozniak, P. (2017) Revisiting Optical Tidal Disruption Events with iPTF16axa. Astrophysical Journal, 842 (1). Art. No. 29. ISSN 0004-637X.

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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 ×10^4 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. We find no correlation between the peak luminosity and the black hole mass, contrary to the expectations for TDEs to have M ∝ M_(BH)^(-1/2).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Blagorodnova, N.0000-0003-0901-1606
Cenko, S. B.0000-0003-1673-970X
Kulkarni, S. R.0000-0001-5390-8563
Arcavi, I.0000-0001-7090-4898
Yan, Lin0000-0003-1710-9339
Lunnan, R.0000-0001-9454-4639
Fremling, C.0000-0002-4223-103X
Cao, Y.0000-0002-8036-8491
Nugent, P. E.0000-0002-3389-0586
Additional Information:© 2017 American Astronomical Society. Received 2017 March 1. Accepted 2017 May 13. Published 2017 June 8. We thank the anonymous referee for helpful comments regarding the manuscript. T.H. thanks T. Holoien and C. Bonnerot for providing data from their papers. S.G. is supported in part by NSF CAREER grant 1454816, NASA Swift Cycle 12 grant NNX16AN85G, and NASA Keck Grant 1568615. N.R. acknowledges the support of a Joint Space-Science Institute prize postdoctoral fellowship. A.H. acknowledges the support of a grant from the I-CORE program "From the Big Bang to Planets." Support for I.A. was provided by NASA through the Einstein Fellowship Program, grant PF6-170148. These results made use of the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Funding AgencyGrant Number
Joint Space-Science InstituteUNSPECIFIED
I-CORE Program of the Planning and Budgeting CommitteeUNSPECIFIED
NASA Einstein FellowshipPF6-170148
W. M. Keck FoundationUNSPECIFIED
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:accretion, accretion disks; black hole physics; galaxies: nuclei; ultraviolet: general
Record Number:CaltechAUTHORS:20170609-064008817
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Official Citation:T. Hung et al 2017 ApJ 842 29
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78038
Deposited By: Ruth Sustaita
Deposited On:09 Jun 2017 16:09
Last Modified:22 Nov 2017 17:53

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