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Catching a supernova just before it happens

Victor Buso is a really very lucky man! On September 20, 2016 we wanted to test his new camera mounted on a 40-cm Newtonian telescope. He pointed to the spiral galaxy NGC 613 because it was at that time located near the zenith. He took a series of 20s exposures spanning approximately an hour and a half. During the first part (about 40 exposures) there was no sign of anything unusual. After a break of 45 min though the exposures that he took revealed the rise of a supernova (SN 2016gkg). He is the first person to ever achieve that, ie. to capture the rise of a supernova just before its maximum light!

These observations are an unprecedented set of data for supernova physics. According to the recent paper by Bersten et al (incl. Buso) 2018 the data shows the clear presence of the shock breakout phase in the optical, i.e. the phase associated with the propagation of the radiation shock inside the star and its dissolution at the surface (Waxman & Katz 2016). This lasts seconds to a fraction of an hour typically, unless there is enough circumstellar mater ejected from the progenitor star before the supernova explosion then this phase may extend to days. The phase produces bright X-ray/UV flash but its optical manifestation has not been observed. So these observations show that the optical light curve is characterized by an extremely rapid brightening at relatively low luminosity.

What I find very critical in this work is actually how quick-witted Buso was. He is an amateur astronomer that didn’t just take the images. Instead he properly reduced them and he noticed the difference. The next important step was to communicate this to the appropriate channels that allowed for follow-up observations to be obtained in in less than a day later (including Swift X-ray, UV and optical telescopes, see Bersten et al 2018 for a list).

References
Bersten et al, 2018, Nature, 554, 497 (NASA/ADS link)
Waxman & Katz, 2016, arXiv:1607.01293 (arXiv link)