Supernova 2011dh was discovered on May 31, 2011 by four astronomers: Tom Reiland in the USA, Thomas Griga of Germany, and Amédée Riou and Stéphane Lamotte Bailey (both of France). It was at about magnitude 14.2 at the time of its discovery (one prediscovery image had it estimated at even 12.9), and had not been in place the night before, and rising in brightness: On June 11, it was found at 12.8, around June 20, at 12.5 mag and brighter. Its brightness peaked around June 23-24, with brightest measurements around 12.1. It stayed at brighter than about 13th magnitude to about July 7, and it had faded down to about mag 17.6 to late January 2012,.
This supernova located 138" east and 92" north of the center of M51. From its spectrum, this supernova was found to be of type IIb, indicating that it was the explosion of a massive supergiant star.
Christopher S. Kochanek has preliminarily identified a candidate for the progenitor star in Hubble Space Telescope (HST) archive images, see his analysis.
Last Modification: February 6, 2012