2019A&A...630A..98S

Aims. We investigate the evolution of X-ray selected tidal disruption events.
Methods. New events are found in near real-time data from XMM-Newton slews, and are monitored by multi-wavelength facilities.
Results. In August 2016, X-ray emission was detected from the galaxy XMMSL2 J144605.0+685735 (also known as 2MASX 14460522+6857311), that was 20 times higher than an upper limit from 25 years earlier. The X-ray flux was flat for ∼100 days and then fell by a factor of 100 over the following 500 days. The UV flux was stable for the first 400 days before fading by a magnitude, while the optical (U,B,V) bands were roughly constant for 850 days. Optically, the galaxy appears to be quiescent, at a distance of 127±4Mpc (z=0.029±0.001) with a spectrum consisting of a young stellar population of 1-5Gyr in age, an older population, and a total stellar mass of ∼6x10⁹M_☉. The bolometric luminosity peaked at L_bol∼10⁴³ergs/s with an X-ray spectrum that may be modelled by a power law of Γ∼2.6 or Comptonisation of a low-temperature thermal component by thermal electrons. We consider a tidal disruption event to be the most likely cause of the flare. Radio emission was absent in this event down to <10µJy, which limits the total energy of a hypothetical off-axis jet to E<5x10⁵⁰ergs. The independent behaviour of the optical, UV, and X-ray light curves challenges models where the UV emission is produced by reprocessing of thermal nuclear emission or by stream-stream collisions. We suggest that the observed UV emission may have been produced from a truncated accretion disc and the X-rays from Compton upscattering of these disc photons.