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

T. W. -S. Holoien; C. S. Kochanek; J. L. Prieto; D. Grupe; Ping Chen; D. Godoy-Rivera; K. Z. Stanek; B. J. Shappee; Subo Dong; J. S. Brown; U. Basu; J. F. Beacom; D. Bersier; J. Brimacombe; E. K. Carlson; E. Falco; E. Johnston; B. F. Madore; G. Pojmanski; M. Seibert

doi:10.1093/mnras/stw2272

paper

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

arXiv:1602.01088 · doi:10.1093/mnras/stw2272

Abstract

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 ( $d ≃ 216$ Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source peaked at a bolometric luminosity of $L ≃ 1.3 \times 1 0^{44}$ ergs s $^{- 1}$ and radiated a total energy of $E ≃ 6.6 \times 1 0^{50}$ ergs over the first $\sim 3.5$ months of observations. The early optical/UV emission of the source can be fit by a blackbody with temperature increasing from $T \sim 2 \times 1 0^{4}$ K to $T \sim 4 \times 1 0^{4}$ K while the luminosity declines from $L ≃ 1.3 \times 1 0^{44}$ ergs s $^{- 1}$ to $L ≃ 2.3 \times 1 0^{43}$ ergs s $^{- 1}$ , requiring the photosphere to be shrinking rapidly. The optical/UV luminosity decline during this period is most consistent with an exponential decline, $L \propto e^{- (t - t_{0}) / τ}$ , with $τ ≃ 46.5$ days for $t_{0} ≃ 57241.6$ (MJD), while a power-law decline of $L \propto (t - t_{0})^{- α}$ with $t_{0} ≃ 57212.3$ and $α = 1.62$ provides a moderately worse fit. 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 $\sim 3$ 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.

arXiv comment18 pages, 13 figures, 5 tables. Photometric data presented in this submission are included as ancillary files. Manuscript updated to reflect changes made in the published version. For a brief video explaining this paper, see https://youtu.be/clYXbqAQ0u0

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

Abstract

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