Region of the Whirlpool Galaxy (M51): supernova SN2011dh

I included the text below before I realized on June 4 that I had captured the supernova in M51 in what was presumably its earliest stages. A closeup crop below shows its location.

This image is first light with my Parsec8300M monochrome camera - just a test, so no color filters, only a luminance image. I'm impressed by its sensitivity: the frames were only 200 seconds but very faint galaxies were easily resolved. A windy night with excellent transparency but terrible seeing.

My back yard, May 31, 2011, 11:30 PM - 1:30 AM; Parsec 8300M on TV-85@f5.6, Hutech LPS filter, 36x200 s.

I have analyzed the magnitude of the supernova in my 36 FIT images, extending over about 2 hours 20 minutes, using the Photometry tool of Maxim Pro v.5. The spreadsheet with the photometric measurements, including identification of 6 reference magnitude stars and 5 check stars, is given here (right click & save). The reported magnitude of the supernova on June 2 was given as about 13.5; however, my measurements indicate that at about midnight on May 31, the magnitude was 13.1 (with one standard deviation of 0.038). The data I obtained is actually better than Mt. Palomar's was for this estimate, because their large telescope produced an oversaturated image. The brightest pixels in the supernova in my 16-bit images are a little less than 16,000.

A graph of magnitude with time, given below, is understandably jumpy but shows a clear trend to increasing magnitude (decreasing brightness) over the 2.3 hours I photographed it, from about 13.04 to 13.12. The increased randomness near the end of the session probably reflects the fact that M51 was decreasing in altitude, and images were subject to increasingly erratic seeing. The increase in magnitude is greater than the uncertainty in measurement, but is still small and may be an artifact of atmospheric absorption or instrumentation. I must leave it to astrophysicists to interpret this profile! My data has been forwarded to the Mount Palomar group for analysis.

I was scooped on this by 1.5 hours, by another photographer in the northeastern US. He's obviously more knowledgeable about photometry, but he obtained a result similar to mine, including an increase in magnitude. A PDF file is here.
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