Rare First Moment of Supernova Captured by Amateur Astronomer

Artist’s impression of a shock breakout. 

Credit: Kavli IPMU

Melina Bersten, researcher at the National Scientific and Technical Research Council-Argentina, and Visiting Associate Scientist at the Kavli Institute for the Physics and Mathematics of the Universe has said the chances of capturing such an event are slim, because it lasts for the order of one hour.

“If we think that on average each galaxy roughly produces one supernova per century, and that a century contains nearly 900 thousand hours, then the chance probability of observing the right galaxy at the right moment is not much greater than one in a million. However, the actual chances are smaller. One needs to take into account the facts that we can only see the galaxy during the night time and that the sky must be clear,” she said.

Luckily, on September 20, 2016, amateur astronomer Víctor Buso from Rosario, Argentina, was testing his new camera on his rooftop observatory in hope of photographing his first supernova. After an hour of taking images Buso noticed a new tiny object had appeared, and it became more obvious with time (Figure 1). He had captured the moment a supernova had exploded.

Sequence of combined images obtained by Víctor Buso as SN 2016gkg arises in the outskirts of galaxy NGC 613. Labels indicate the time each image was taken. The supernova location is indicated by the red circles. Notably the supernova appears and steadily brightens within one hour, as shown in the lower-right panel. 

Credit: Bersten et al.

Named SN 2016gkg, a team of researchers including the Kavli Institute for the Physics and Mathematics of the Universe, and lead by Bersten, analyzed the images. The rapid brightening rate combined with a very low luminosity had no analogue among known supernovae, and the team concluded Buso had discovered SN 2016gkg during the shock breakout.

“When Buso told us how he had observed and what he had witnessed, we realized this was a unique finding,” said Bersten.

Also, by comparing the photometry of the images with their computer simulations, the team found an initial sharp rise in supernova light that could only be explained by shock emergence (Figure 2).

 Observed light curve of SN 2016gkg (dots) and explosion model (red line). The model reproduces three distinct phases in the supernova evolution that occur on different time scales. First, the shock breakout (with a time scale of hours), then the post-shock cooling emission (days), and finally the emission due to radioactive heating (weeks). Buso’s discovery observations, shown in blue, indicate such a rapid rise that can only be attributed to the shock breakout. 

Credit: Bersten et al.

“To our surprise, images had a great quality considering they were obtained from the middle of a large city in the midst of the pampas”, notes Dr. Gastón Folatelli from IALP, who led the data analysis, and adds “sky conditions seem to have been nearly ideal on that night!”

Their conclusion was supported by the fact that the models required no modification in order to consistently reproduce the initial rise and the rest of the supernova evolution (Figure 3). Moreover, SN 2016gkg happened to be a rather ordinary event, which would imply that the observed phase is common to all supernovae, as models predict.

The team’s results were published in Nature on February 22.

Contacts and sources:
Ken’ichi Nomoto

Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo

Motoko Kakubayashi
Kavli Institute for the Physics and Mathematics of the Universe
The University of Tokyo

Citation:  M. C. Bersten et al., “A surge of light at the birth of a supernova”, Nature, 22 February 2018 DOI: 10.1038/nature25151