The supernova is known as "PTF 11eon" to the PTF team, but as SN2011dh to the larger world. A finder chart for it is shown below.
Click to enlarge the image.
Any amateur astronomers who have raw images of M51 taken between May 30 and June 2 are encouraged to contact the PTF team at this address: firstname.lastname@example.org.
For more on the supernova, check out this article from Sky & Telescope or this one from Universe Today.