Fast radio bursts (FRBs) are bursts of extremely energetic and brief radio waves, in the order of a few milliseconds, emitted from deep space. Numerous FRBs have been detected in recent years, and their origin and their production mechanism are still an enigma for astrophysicists. However, so far, all the clues have pointed to an extragalactic origin. However, recently, radio telescopes around the world, as well as their X-ray observing counterparts, have detected a FRB whose origin may well be SGR 1935 + 2154, a magnetar located in the Milky Way. This would then constitute the very first observation of a FRB originating from our galaxy.
On April 28, 2020, the magnetar – located just 30,000 light years – was at the origin of an event detected by several radio telescopes around the world: a burst of radio waves of a millisecond. Concomitantly, X-ray observatories (terrestrial and space) detected a similar event in X-rays.
Magnetars: they are a possible source of FRB
Although the data collected is still in the study and analysis phase, astrophysicists believe that they may have finally identified the source of the rapid radio bursts (FRBs) observed for several years. FRBs are intriguing phenomena. These are bursts of extremely energetic radio waves, some emitting more energy than 500 million suns. However, they are very brief (a few milliseconds) and do not repeat themselves; they are therefore very difficult to observe and trace.
First, astrophysicists believed that the FRBs came from particularly chaotic supernovae. But recently, a new hypothesis involves magnetars. This is a special type of star at neutrons whose magnetic field is extremely intense: about 1000 times more intense than a star at neutrons classic.
The origin of magnetar formation, however, is still unknown. The magnetic field is so strong that it distorts the shape of the star, effectively opposing the force of gravity. This produces a tension between the two forces that cause gigantic earthquakes and magnetic eruptions.
A FRB of potentially galactic origin detected by many radio telescopes
On April 27, 2020, SGR 1935 + 2154 was detected and observed by several instruments, including the Swift Burst Alert Telescope, the AGILE satellite and the Neutron Star Interior Composition Explorer of the ISS. The activity initially appeared to be relatively normal, consistent with behavior seen in other magnetars.
Dynamic spectrum of the FRB of SGR 1935 + 2154 recorded by CHIME. The burst shows a double-peak structure with two components separated by 30 ms. Credit: Paul Scholz
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But then, on April 28, the Canadian Hydrogen Intensity Mapping (CHIME) experiment – a telescope designed to scan the sky for transient events – made an astonishing detection, such a powerful signal. that the system could not quantify it. Detection has been reported sure The Astronomer’s Telegram.
But the STARE2 mission, a project launched by Christopher Bochenek, is designed exactly for the detection of local FRBs. It consists of three radio dipole antennas located hundreds of kilometers apart, which can first of all exclude local signals produced by human activity and also allow triangulation of the signals.
“Forêt de FRB” from SGR 1935 + 2154, registered by AGILE. The two peaks of the spectrum are clearly visible. Credits: A. Ursi et al. 2020
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It clearly detected the signal, with a fluency of over a million jansky milliseconds. Typically, we receive extragalactic FRBs a few tens of milliseconds jansky. Once corrected for distance, SGR 1935 + 2154 is at the lower end of the power FRB – but it fits the profile of a FRB well, according to astrophysicists.
” If the same signal came from a neighboring galaxy, like one of the galaxies Typical FRB nearby, it would look like FRB to us. Something like this has never been seen before “Said Shrinivas Kulkarni, astrophysicist and member of the STARE2 mission.
On the same subject : Detection of the first rapid radio burst showing a regular cycle of appearance in a distant galaxy
Unusual detection of a counterparty to the FRB in X-rays
However, the researchers also observed a phenomenon never detected before in the case of an extragalactic FRB: a counterpart in X-rays. However, the emission of X-rays and gamma rays is as common for magnetars as that of radio waves.
Light curve of the X-ray counterpart detected by INTEGRAL IBIS (blue) and SPI-ACS (orange). Credits: S. Mereghetti et al. 2020
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The X-ray counterpart of the FRB SGR1935 + 2154 was neither particularly strong nor unusual, says astrophysicist Sandro Mereghetti of the National Institute of Astrophysics in Italy. But that could imply that there are many more FRBs than we can currently detect.
” This is a very intriguing result which supports the association between FRB and magnetars. The FRBs identified so far are extragalactic. They have never been detected in X / gamma rays. An X-ray burst with a brightness like that of the SGR1935 would be undetectable for an extragalactic source “
Astrophysicists are currently analyzing the data in more depth, in order to compare the spectral signatures of the extragalactic FRBs with that newly detected. A clear difference between the signatures could mean a return to square one. And if the origin of the FRB turns out to be a magnetar, that does not mean that all the sources of the FRB are magnetars. In any case, for the next few months, exciting news is to be expected.
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