The skies are full of transient events. If you don’t happen to have a telescope pointed at the right place at the right time, you can miss anything from the transit of a planet to the explosion of a star. But thanks to the development of automated survey telescopes, the odds of getting lucky have improved considerably.
In October of 2013, the telescope of the intermediate Palomar Transient Factory worked just as expected, capturing a sudden brightening that turned out to reflect the explosion of a red supergiant in a nearby galaxy. The first images came from within three hours of the supernova itself, and followup observations tracked the energy released as it blasted through the nearby environment. The analysis of the event was published on Monday in Nature Physics, and it suggests the explosion followed shortly after the star ejected large amounts of material.
This isn’t the first supernova we’ve witnessed as it happened; the Kepler space telescope captured two just as the energy of the explosion of the star’s core burst through the surface. By comparison, observations three hours later are relative latecomers. But SN 2013fs (as it was later termed) provided considerably more detail, as followup observations were extensive and covered all wavelengths, from X-rays to the infrared.
Source: Observations catch a supernova three hours after it exploded | Ars Technica