Although this image of M101 was taken on May 12, 2012, it shows the supernova that exploded in the galaxy on August 24, 2011. The white line points inward to the supernova.
At maximum brightness it reached magnitude 9.9 but by November it had faded to about 14 mag. No estimate where it stood on May 12 when this photograph was taken, but it seems to be dimming quite slowly. The outburst consumed a star that was formerly a white dwarf.