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ASASSN-15oi: A Rapidly Evolving, Luminous Tidal Disruption Event at 216 Mpc

Holoien, TW-S and Kochanek, CS and Prieto, JL and Grupe, D and Chen, P and Godoy-Rivera, D and Stanek, KZ and Shappee, BJ and Dong, S and Brown, JS and Basu, U and Beacom, JF and Bersier, D and Brimacombe, J and Carlson, EK and Falco, E and Johnston, E and Madore, BF and Pojmanski, G and Seibert, M (2016) ASASSN-15oi: A Rapidly Evolving, Luminous Tidal Disruption Event at 216 Mpc. Monthly Notices of the Royal Astronomical Society, 463 (4). pp. 3813-3828. ISSN 0035-8711

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We present ground-based and Swift photometric and spectroscopic observations of the tidal disruption event (TDE) ASASSN-15oi, discovered at the center of 2MASX J20390918-3045201 ($d\simeq216$ Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source peaked at a bolometric luminosity of $L\simeq1.9\times10^{44}$ ergs s$^{-1}$ and radiated a total energy of $E\simeq5.0\times10^{50}$ ergs over the $\sim3.5$ months of observations. The early optical/UV emission of the source can be fit by a blackbody with temperature increasing from $T\sim2\times10^4$ K to $T\sim6\times10^4$ K while the luminosity declines from $L\simeq1.9\times10^{44}$ ergs s$^{-1}$ to $L\simeq2.8\times10^{43}$ ergs s$^{-1}$, requiring the photosphere to be shrinking rapidly. The optical/UV luminosity decline is broadly consistent with an exponential decline, $L\propto e^{-t/t_0}$, with $t_0\simeq35$ days. ASASSN-15oi also exhibits roughly constant soft X-ray emission that is significantly weaker than the optical/UV emission. Spectra of the source show broad helium emission lines and strong blue continuum emission in early epochs, although these features fade rapidly and are not present $\sim3$ months after discovery. The early spectroscopic features and color evolution of ASASSN-15oi are consistent with a TDE, but the rapid spectral evolution is unique among optically-selected TDEs.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record "ASASSN-15oi: A Rapidly Evolving, Luminous Tidal Disruption Event at 216 Mpc" is available online at http://dx.doi.org/10.1093/mnras/stw2272
Uncontrolled Keywords: astro-ph.HE; astro-ph.HE
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 10 Feb 2016 10:24
Last Modified: 10 May 2017 10:03
DOI or Identification number: 10.1093/mnras/stw2272
URI: http://researchonline.ljmu.ac.uk/id/eprint/2897

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