Context :

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 L _ { bol } \sim 2 \times 10 ^ { 44 } ergs s ^ { -1 } with a spectrum that may be modelled with thermal emission in the UV band , a power-law with \Gamma \sim 2 dominating in the X-ray band above 2 keV and a soft X-ray excess with an effective temperature of \sim 86 eV .
Rapid variability locates the X-ray emission to within < 73 R _ { g } of the nuclear black hole .
Radio emission of flux density \sim 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 .

Conclusions :