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XMMSL1 J074008.2-853927: a tidal disruption event with thermal and non-thermal components

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journal contribution
posted on 2018-05-15, 12:59 authored by R. D. Saxton, Andrew M. Read, S. Komossa, P. Lira, K. D. Alexander, M. H. Wieringa
Aims: We study X-ray bright tidal disruption events (TDE), close to the peak of their emission, with the intention of understanding the evolution of their light curves and spectra. Methods: Candidate TDE are identified by searching for soft X-ray flares from non-active galaxies in recent XMM-Newton slew data. Results: In April 2014, X-ray emission was detected from the galaxy XMMSL1 J074008.2-853927 (a.k.a. 2MASX 07400785-8539307), a factor 20 times higher than an upper limit from 20 years earlier. Both the X-ray and UV flux subsequently fell, by factors of 70 and 12 respectively. The bolometric luminosity peaked at Lbol ~ 2 × 1044 ergs s-1 with a spectrum that may be modelled with thermal emission in the UV band, a power-law with Γ ~ 2 dominating in the X-ray band above 2 keV and a soft X-ray excess with an effective temperature of ~86 eV. Rapid variability locates the X-ray emission to within <73 Rg of the nuclear black hole. Radio emission of flux density ~1 mJy, peaking at 1.5 GHz was detected 21 months after discovery. Optical spectra indicate that the galaxy, at a distance of 73 Mpc (z = 0.0173), underwent a starburst 2 Gyr ago and is now quiescent. We consider a tidal disruption event to be the most likely cause of the flare. If this proves to be correct then this is a very clean example of a disruption exhibiting both thermal and non-thermal radiation.



Astronomy and Astrophysics, 2017, 598, A29

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