New Supernova in M82

Posted January 22, 2014 by User 1

A new supernova was discovered January 22, 2014 in the nearby galaxy M82 located in the constellation Ursa Major. Based on pre-discovery observations, the supernova had been brightening since about a week prior to being reported. The supernova was observed to be magnitude 14 on the 15th, reached 13 by the 17th and has since brightened to magnitude 12 at discovery. Recent observations suggest the supernova is now approximately magnitude 11 and is continuing to brighten.

Analysis of the spectrum and light curve of the supernova suggest that the event is a Type Ia supernova which is caused by a white dwarf accumulating too much material on its surface to remain stable, causing it to first collapse, then explode. Because of the stars explode having essentially the exact same mass (the Chandrasekhar limit), such supernovas have a consistent peak absolute magnitude of -19.3 and are thus useful for determining distances to faraway galaxies. However, this present supernova is obscured by dust and therefore will appear somewhat fainter than its brightness and distance would suggest.

M82 is located approximately 11.5 million parsecs away from the Earth. Assuming a peak absolute magnitude of -19.3, the peak apparent magnitude would be

m = -19.3 + log₁₀ (11.5 * 10⁶ / 10) + k_dust

The k_dust is the difference between the expected brightness minus dust and the observed brightness. Assuming the dust absorbs 80% of the light emitted by the supernova (so 5 times dimmer), we have k_dust = log(4)/log(2.512) = 1.7. Then,

m = -19.3 + log₁₀ (11.5 * 10⁶ / 10) + 1.7 = 10.1

In other words, assuming our assumption of 80% absorption is reasonable, we can expect a peak magnitude of about 10 in the coming weeks.

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