Space telescopes, Insight-HXMT and GECAM-C, observed the brightest gamma-ray burst ever detected


     The Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS) has collaborated with around 40 research institutions worldwide to announce their latest discoveries about the brightest gamma-ray burst, named GRB 221009A, ever detected by humans. Using unique observations made by two Chinese space telescopes, Insight-HXMT and GECAM-C, scientists were able to accurately measure the brightness and energy released by the burst, which is crucial to understanding this significant event.

    In addition to the space telescopes, another ground-based facility called the Large High Altitude Air Shower Observatory (LHAASO), led by IHEP, carried out a joint observation with Insight-HXMT and GECAM-C telescopes, resulting in several important first discoveries with its large amount of very high energy observation data.

    Gamma-ray bursts (GRBs) are the most energetic explosion phenomena in the universe, which can be produced by either the core collapse of a massive star or the merger of two compact stars, such as neutron stars and black holes. GRB 221009A belongs to the former category.

    The international team, led by IHEP and comprising researchers from over 30 institutes from China, the US, Italy, France, and Germany, accurately measured the prompt emission and early afterglow of this unprecedented burst in the hard X-ray and soft gamma energy bands using the Insight-HXMT and GECAM-C space telescopes.

    GECAM-C, which operated in a special observation mode capable of recording extremely bright GRBs, was able to measure the burst accurately, whereas other space telescopes were unable to do so.

    The measurements taken by GECAM-C indicated that this burst set new records on both the observed brightness and the isotropic-equivalent energy of all detected bursts, making this burst truly exceptional. It was 50 times brighter than the previous record-holder, and the isotropic-equivalent energy of this burst was more than 1055 erg, which is approximately equal to the total rest mass energy of 8 solar masses.

    Insight-HXMT, China’s first X-ray space telescope designed to observe the X-ray source in the Milky Way, made a clear measurement of GRB 221009A for its precursor and early afterglow, thanks to its very large detection area in the MeV energy range. By combining the data from both telescopes, the researchers were able to obtain a complete picture of this precious burst.

    According to the joint observation by Insight-HXMT and GECAM-C, the early afterglow of GRB 221009A switched from slow decay to rapid decay very early in time, indicating that this burst launched an extremely narrow and luminous jet directly pointing to us.

    These discoveries shed new light on the physics of energetic explosions in the universe, and more detailed modeling is needed to understand how GRB engines manage to collimate the jets to produce such a huge isotropic equivalent energy in some cases. The team’s paper is currently available on the arXiv pre-print server.