Astronomers with the Palomar Transient Factory are reporting the discovery of a supernova in the Whirlpool Galaxy (M51).
It has been classified as a Type II supernova, which means that it is the result of the collapse and explosion of a massive star. The classification was performed using the Keck I telescope in Hawai'i. The magnitude of the star was estimated at 13.5, which makes it bright enough for amateur astronomers to see and image. It should be noted in the discovery report that the "exact magnitude uncertain due to saturation" - meaning that the supernova was too bright for astronomers to measure. Of course they were using one of the largest telescopes on the planet.
I am checking to see if there will be images to post, but in the meantime here is a shot of M51 taken well over a year ago by Palomar's 48-inch Samuel Oschin Telescope as a part of the Palomar Transient Factory Survey:
I am sure that there will be more news on this in the coming days and weeks, so stay tuned.