Astronomers using space telescopes and satellites have discovered a new extragalactic giant flare of gamma rays associated with a magnetar. This was done thanks to observational data from space telescopes and satellites, which helped scientists determine the position of the radiation source with great accuracy. The article was published in the journal Nature.
Magnetars are a rare type of neutron stars that have very strong magnetic fields (1014-1015 gauss); today only a few dozen magnetars are known in the Milky Way. Some of these objects generate irregular bursts of hard X-ray or soft gamma rays and are termed soft gamma repeaters. During the phase of activity, which can last for days or years, such sources generate short (lasting from a few milliseconds to seconds) bursts of hard X-ray radiation with a peak luminosity of 1038-1042 erg per second. However, much more powerful events are also possible, recorded much less often, called giant flares, during which (0.01−1) × 1046 erg is released in the form of gamma radiation in a fraction of a second.
Unfortunately, there is little observation data for such events: scientists know only 12 magnetars that generate radiation bursts in the Milky Way and the Large Magellanic Cloud, and only two candidates for the role of extragalactic giant flares of magnetars.
Astronomers from Germany, Italy, Russia, the United States and Switzerland, led by Dmitry Svinkin from the Ioffe Physico-Technical Institute, reported a new extragalactic giant flare of magnetar GRB 200415A recorded on April 15, 2020. In order to understand the nature of the flare and determine its source, scientists needed to analyze data obtained by the Fermi, Swift and INTEGRAL space telescopes, the Konus instrument installed on the Wind satellite, the Mars Odyssey probe and the Atmosphere-Space Interactions Monitor (ASIM) instrument installed on ISS.
Researchers have determined that the source of the burst lies in an area of 20 square minutes of arc in the barred spiral galaxy NGC 253, located 11.4 million light years from the Sun in the constellation Sculptor, which is actively forming new stars. The peak luminosity of GRB 200415A was 1.4 × 1048 erg per second, the burst is characterized by a sharp initial increase in radiation intensity (millisecond scale) followed by a decay of 0.2 seconds duration. It is assumed that the release of energy occurred as a result of the restructuring of the magnetic field of the magnetar, possibly caused by a starquake.
GRB 200415A turned out to be very similar to the GRB 051103 burst, the source of which was in the group of galaxies M81 / M82, both of these events were eventually recognized by scientists as the most significant candidates for extragalactic giant flares of magnetars today, and they turned out to be more than five times brighter than any flare previously seen in magnetars in the Milky Way. Nevertheless, astronomers cannot yet completely rule out the version that both bursts may belong to the cosmological population of short gamma-ray bursts.