Abstract

We present the discovery of PS18kh, a tidal disruption event discovered at the center of SDSS J075654.53 +341543.6 (d similar or equal to 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 similar or equal to 12,000 K to T similar or equal to 25,000 K and it peaked at a luminosity of L similar or equal to 8.8 x 10(43) erg s(-1). PS18kh radiated E = (3.45 +/- 0.22) x 10(50) erg over the period of observation, with (1.42 +/- 0.20) x 10(50) erg being released during the rise to peak. Spectra of PS18kh show a changing, boxy/double-peaked Ha emission feature, which becomes more prominent over time. We use models of non-axisymmetric accretion disks to describe the profile of the Ha 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) similar to 60r(g) to an outer radius of r(out) similar to 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.