PS18kh: A New Tidal Disruption Event with a Non-axisymmetric Accretion Disk

Author(s): Pan-Starrs; Asas-Sn; Atlas; Holoien, TWS; Huber, ME; Shappee, BJ; Eracleous, M; Auchettl, K; Brown, JS; Tucker, MA; Chambers, KC; Kochanek, CS; Stanek, KZ; Rest, A; Bersier, D; Post, RS; Aldering, G; Ponder, KA; Simon, JD; Kankare, E; Dong, D; Hallinan, G; Reddy, NA; Sanders, RL; Topping, MW; Bulger, J; Lowe, TB; Magnier, EA; Schultz, ASB; Waters, CZ; Willman, M; Wright, D; Young, DR; Dong, S; Prieto, JL; Thompson, TA; Denneau, L; Flewelling, H; Heinze, AN; Smartt, SJ; Smith, KW; Stalder, B; Tonry, JL; Weiland, H | Abstract: © 2019. The American Astronomical Society. All rights reserved.. We present the discovery of PS18kh, a tidal disruption event discovered at the center of SDSS J075654.53+341543.6 (d ≃ 322 Mpc) by the Pan-STARRS Survey for Transients. Our data set includes pre-discovery survey data from Pan-STARRS, the All-sky Automated Survey for Supernovae, and the Asteroid Terrestrial-impact Last Alert System as well as high-cadence, multiwavelength follow-up data from ground-based telescopes and Swift, spanning from 56 days before peak light until 75 days after. The optical/UV emission from PS18kh is well-fit as a blackbody with temperatures ranging from T ≃ 12,000 K to T ≃ 25,000 K and it peaked at a luminosity of L ≃ 8.8 × 1043 erg s-1. PS18kh radiated E = (3.45 ± 0.22) × 1050 erg over the period of observation, with (1.42 ± 0.20) × 1050 erg being released during the rise to peak. Spectra of PS18kh show a changing, boxy/double-peaked Hα emission feature, which becomes more prominent over time. We use models of non-axisymmetric accretion disks to describe the profile of the Hα line and its evolution. We find that at early times the high accretion rate leads the disk to emit a wind which modifies the shape of the line profile and makes it bell-shaped. At late times, the wind becomes optically thin, allowing the non-axisymmetric perturbations to show up in the line profile. The line-emitting portion of the disk extends from r in ∼ 60r g to an outer radius of r out ∼ 1400r g and the perturbations can be represented either as an eccentricity in the outer rings of the disk or as a spiral arm in the inner disk.