June 3, 2010: A new supernova in M51 was discovered by A. Riou and confirmed by several sources, including the Palomar Transient Factory (Silverman et al., ATEL 3398). It is located at 13:30:05.08 +47:10:11.2 J2000 and has a magnitude of about 13.5. Nice images of the supernova can be found at: http://6888comete.free.fr/fr/imageSN.htm PTF also obtained a spectra from Keck, indicating that this is a type II supernova with a relatively blue continuum with P-Cygni profiles in the Balmer series. This is a unique event, because it occurs in a galaxy that is imaged almost constantly. There must be many photos available that show the rise of this SNe, so the data-mining opportunity is obvious. It is transiting at local twilight and should be observable for northern hemisphere observers for several months. A new APASS sequence should be uploaded soon. We recommend taking nightly monitoring images in B and V for CCD observers, along with visual estimates, until the supernova is no longer visible. Here is an excuse to take the 10 millionth image of M51!
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Arne A. Henden