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XMMSL2 J144605.0+685735: a slow tidal disruption event

Saxton, RD, Read, AM, Komossa, S, Lira, P, Alexander, KD, Steele, IA, Ocana, F, Berger, E and Blanchard, P (2019) XMMSL2 J144605.0+685735: a slow tidal disruption event. Astronomy & Astrophysics, 630. ISSN 1432-0746

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Abstract

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.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: EDP Sciences
Related URLs:
Date Deposited: 06 Jan 2020 11:47
Last Modified: 06 Jan 2020 12:00
DOI or Identification number: 10.1051/0004-6361/201935650
URI: http://researchonline.ljmu.ac.uk/id/eprint/11953

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