Image of a radio burst observed at the Parkes radio telescope in Australia. Astrophysicist Duncan Lorimer found it in archival data from 2007. It was a massive 30-jansky burst lasting 5 milliseconds and coming from a place in the sky within 3° of the Small Magellanic Cloud. It has since achieved a certain measure of fame, and has become known as the Lorimer Burst.
Similar radio bursts -- called Fast Radio Bursts --- have since been observed, and their source is something of a mystery. Astrophysicists estimate the source of the bursts to be an area no more than a few hundred kilometers in area and extraordinarily high in energy, especially so if the source is outside the Milky Way as seems likely.
Last May, scientists using multiple telescopes observed a Fast Radio Burst in real time -- until recently they had all been found retrospectively in archival data. Here's a tantalizing quote from the space.com write-up:
Although the source of these bursts remains a mystery, scientists say it must be huge, cataclysmic and up to 5 billion light-years away. This study sheds light on their exact origins, noting that a top contender is a flare from a magnetar, a neutron star with a magnetic field a million billion times more powerful than Earth's.
For my money, this is one of the most fascinating mysteries in astrophysics rights now.