  New high variability extragalactic sources may be identified by comparing the
flux of sources seen in the XMM-Newton Slew Survey with detections and upper
limits from the ROSAT All Sky Survey. In November 2012, X-ray emission was
detected from the galaxy XMMSL1 J061927.1-655311 (a.k.a. 2MASX
06192755-6553079), a factor 140 times higher than an upper limit from 20 years
earlier. Both the X-ray and UV flux subsequently fell, over the following year,
by factors of 20 and 4 respectively. Optically, the galaxy appears to be a
Seyfert I with broad Balmer lines and weak, narrow, low-ionisation emission
lines, at a redshift of 0.0729. The X-ray luminosity peaks at Lx ~ 8x10^43
ergs/s with a typical Sy I-like power-law X-ray spectrum of index ~ 2. The
flare has either been caused by a tidal disruption event or by an increase in
the accretion rate of a persistent AGN.
