A powerful gamma-ray burst could originate from an incredibly magnetic, dead star – iPon

Last November, astronomers detected a fast gamma-ray burst lasting only a tenth of a second. 13 seconds later, they knew it came from the galaxy M82, which is only 12 million light years away. It’s practically next door, and the signs suggested that the researchers were witnessing something very rare: the eruption of a magnetar.

A magnetar is a special type of neutron star that has an incredibly strong magnetic field. Neutron stars are the end products of certain supernovae, i.e. the extremely dense and degenerate cores of dead stars. Short gamma-ray bursts are usually caused by collisions of neutron stars that release lots of energy and gravitational waves, but the research team suspected an even rarer phenomenon in which a magnetar plays a role.

Over the past 50 years, only three other outbursts from magnetars have been identified as short gamma-ray bursts. They were detected either from our own galaxy or from the Large Magellanic Cloud, the largest and one of the closest galactic companions of the Milky Way. This is the fourth and most distant yet, but still much closer than any other short gamma-ray burst.

“We immediately realized that this was a special case. Gamma-ray bursts can usually come from far away and anywhere in the sky, but this one came from a bright, nearby galaxy,” says the lead author of the study, Sandro Mereghetti, from the National Institute of Astrophysics in Milan (INAF-IASF).

If that’s the case, it’s the first magnetar detected in a galaxy outside the Milky Way’s influence zone, and the team used a number of telescopes to confirm if it really is. After the initial alarm from the Integral satellite of the European Space Agency (ESA), the phenomenon was monitored both in the X-ray range, including with ESA’s XMM-Newton telescope, and with observatories operating in the visible range, to assess whether there were any signs of neutron star collisions. The team also checked data from gravitational wave detectors, but they didn’t see any signs of this. Based on these, the experts are sure that the signal comes from a magnetar.

M82 is a galaxy that produces an extraordinary number of stars. Some of these live intense lives and die young, that is, go supernova, leaving behind neutron stars—in some cases, magnetars. The magnetic fields of these objects are one trillion times stronger than Earth’s. The discovery suggests that galaxies like M82 could be ideal places to look for magnetars, so astronomers are now paying special attention to such systems to see if they spot more similar outbursts.