New Sky Survey Captures Key Details of Two Spectacular Cosmic Explosions

Sky surveys can capture quite a bit of information about our Universe. Now, a recent survey has captured key details about two cosmic explosions. It's gathered information about the progenitor of a rare type of supernova in a nearby galaxy and has also spotted the afterglow of a gamma-ray burst. The findings reveal a little bit more about these dying stars.

Supernovae are massive exploding stars at the end of their lifespans. They make up one very important type of transient. In this case, the astronomers detected a so-called Type Ib supernova. Type Ib supernovae are rare explosions where the progenitor star lacks an outer layer of hydrogen, the most abundant element in the universe, hence the "stripped envelope" moniker. Until now, though, scientists have been unsure about which kinds of stars give rise to Type Ib supernovae.

This sky survey, though, may have answered that question. The supernova that the astronomers discovered, named iPTF13bvn, occurred at a location formerly occupied by a likely Wolf-Rayet star. These stars are 10 times more massive and thousands of times brighter than the sun and have lost their hydrogen envelope by means of very strong stellar winds.

"All evidence is consistent with the theoretical expectation that the progenitor of this Type Ib supernova is a Wolf-Rayet star," said Yi Cao, one of the researchers, in a news release. "Our next step is to check for the disappearance of this progenitor star after the supernova fades away. We expect that it will have been destroyed in the supernova explosion."

That's not all the survey found, though. It also detected the afterglow of a long gamma-ray burst (GRB). Long GRBs, which are the brightest known electromagnetic events in the universe, are also connected with the deaths of rapidly spinning, massive stars. Although GRBs are initially detected by their high-energy radiation, an X-ray or visible-light afterglow must also be found to narrow down a GRB's position enough so that its location can be pinpointed in one particular galaxy.

In this case, the researchers were able to pinpoint the location of the GRB that they spotted by scanning an area of the sky over 360 times larger than the face of the moon and sifting through hundreds of images.

"First, by measuring its redshift, we learned that it was pretty nearby as far as GRBs go," said Singer, one of the researchers, in a news release. "It was pretty wimpy compared to most GRBs, liberating only about a thousandth as much energy as the most energetic ones. But we did see it eventually turn into a supernova. Typically we only detect supernovae in connection with nearby, subluminous GRBs, so we can't be certain that cosmologically distant GRBs are caused by the same kinds of explosions."

The findings reveal a little bit more about these distant objects. In addition, they show that these sky surveys are crucial for better understanding our universe.

The findings are published in two papers in Astrophysical Journal Letters.