A possible mechanism for long duration gamma-ray bursts

Representation of the jet of a gamma-ray burst such as GRB 190114C (Image courtesy Kitty Yeung)
Representation of the jet of a gamma-ray burst such as GRB 190114C (Image courtesy Kitty Yeung)

An article published in “The Astrophysical Journal Letters” reports a study on a gamma-ray burst cataloged as GRB 190114C and detected by NASA’s Swift satellite and the MAGIC telescopes at the Canaries. Professor Evgeny Derishev and Professor Tsvi Piran put together the data from these detecions, which are about photons at very different energies, concluding that the radiations detected must have originated in a jet that moved at a speed of about 99.99% of the speed of light. These are so-called ultra-high energy emissions in the Teraelettronvolt (TeV) range and they think that the mechanism of origin is the inverse Compton scattering while emissions of less energetic photons originate from synchrotron radiation.

Gamma-ray bursts are extremely energetic phenomena and in the long duration ones an energy is emitted higher than that emitted by the Sun during its entire life. The duration of gamma-ray bursts is very variable and GRB 190114C has been a long duration one, which can be emitted following the collapse of a massive star in agony or from the merger of exotic objects such as neutron stars and black holes. On January 14, 2019 NASA’s Swift satellite detected gamma rays emitted about 4.5 billion years ago and the immediate alert made it possible to detect them with other instruments such as the MAGIC (Major Atmospheric Gamma Imaging Cherenkov Telescopes) telescopes, designed precisely to study very high energy phenomena such as gamma-ray bursts.

The GRB 190114C event was important among other things because for the first time, thanks to the ALMA radio telescope, polarized radio signals were detected. A magnetic field can make the oscillations of electromagnetic waves to have a particular orientation of the electric field, called polarization. Now, however, it seems that the studies of high-energy photons, including ultra-high energy ones, are the ones that make it possible to obtain new information on gamma-ray bursts.

The photons detected by the two MAGIC telescopes are at least ten times more energetic than those at the highest energies ever detected in a gamma-ray burst. They were crucial to this new research in which Professor Evgeny Derishev of the Russian Academy of Sciences and Professor Tsvi Piran of the Hebrew University of Jerusalem identified as mechanism or origin the inverse Compton scattering in which ultra-high energy electrons collide with low-energy photons that boost their energy. The interesting thing is that those relativistic electrons produce the low-energy photons with the synchrotron radiation mechanism.

Professor Tsvi Piran stated that the MAGIC telescopes made it possible to find a Rosetta stone of gamma-ray bursts allowing the researchers to discriminate between different emission models and discover the exact conditions in the explosion. These are remarkable statements and if they get confirmed it means that we’re really understanding these extreme phenomena. More information can be collected in the future with detections of new long duration gamma-ray bursts, especially when new instruments, even more perfected than MAGIC, will be activated.

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