The shock breakout cooling tail of supernova 2011dh in Messier 51

Unfiltered CCD observations acquired using the 6-inch [155mm] robotic telescopes of the NASA/Harvard Smithsonian MicroObservatory e-learning project covering the first 163 days following the discovery of the Type IIb supernova 2011dh in Messier 51 are presented. The lightcurve shows two peaks, the first, a transient ‘spike’ with an observed magnitude of ~13.1 corresponds to the shock breakout cooling tail as the atmosphere of the star expands and cools following the rapid heating by the shock from the gravitational collapse of the iron core. The second peak has an observed magnitude of 12.6±0.02 some 19.5 days after first light and declines to an observed magnitude of 14.8 by the end of the set of observations. At peak brightness, the SN has an absolute magnitude of -17.0±0.34, corresponding to a luminosity of ~5.3×10^8 solar luminosities.

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