Volume 630, October 2019
|Number of page(s)||10|
|Published online||26 September 2019|
XMMSL2 J144605.0+685735: a slow tidal disruption event
Telespazio-Vega UK for ESA, European Space Astronomy Centre, Operations Department, 28691 Villanueva de la Cañada, Spain
e-mail: email@example.com, firstname.lastname@example.org
2 Dept. of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
3 Max Planck Institut für Radioastronomie, Auf dem Huegel 69, 53121 Bonn, Germany
4 Universidad de Chile, Observatorio Astronomico Nacional Cerro Calan, Santiago, Chile
5 Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
6 Liverpool John Moores University, Liverpool L3 5RF, UK
7 Dpto. de Física de la Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
8 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
Accepted: 15 August 2019
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 ± 4 Mpc (z = 0.029 ± 0.001) with a spectrum consisting of a young stellar population of 1–5 Gyr in age, an older population, and a total stellar mass of ∼6 × 109 M⊙. The bolometric luminosity peaked at Lbol ∼ 1043 ergs s−1 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 < 10 μJy, which limits the total energy of a hypothetical off-axis jet to E < 5 × 1050 ergs. 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.
Key words: galaxies: individual: XMMSL2 J144605.0+685735 / galaxies: individual: 2MASX 14460522+6857311 / X-rays: galaxies
© ESO 2019
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