10 billion years in a flash

On November 8 there was a high power of Gamma Ray Burst with a redshift of 2.4, equivalent to 10 billion light years away and with energy given off a thousand times greater than that produced by the Sun in its entire life. To record the event satellites AGILE and Fermi were functional and thus being able to collect sufficient data.



GRBs (Gamma – Rays Burst) are flashes of gamma rays of high intensity but lasting only a few seconds. It is believed that they are linked to the end of massive stars, even if the mechanisms that produce these phenomena are still partly wrapped in mystery. On the night of November 8, the instruments on board the satellites Fermi and AGILE have revealed that the GRB 131108A, for a few tens of seconds, showed an exceptionally high intensity for events of this kind.

AGILE’s equipment consist of a Gamma Ray Imaging Detector (GRID) sensitive in the 30 MeV – 50 GeV energy array, a SuperAGILE (SA) hard X-ray monitor sensitive in the 18–60 keV energy array, a Mini-Calorimeter (MCAL) non-imaging gamma-ray flashing detector sensitive in the 350 keV – 100 MeV energy array, and an Anti-coincidence System (AC), based on a flexible scintillator, to help with suppressing undesirable circumstantial events.

This event has been recognized and located by the onboard software of the instrument Fermi / LAT (GCN 15464, Racusin et al. GCN and 15472, Vianello et al.) Without any human intervention (only circumstance occurred on another occasion so far), a testament to how rare and interesting it was. Thanks to the rapid localization provided by the LAT, the Swift satellite has been able to re-aim the position of the GRB and start the search for a possible afterglow only 90 minutes after the trigger (the typical time for this operation is usually 8 to 10 hours). It was possible to refine the localization at the level of sub-arc minutes, making it possible to focus and make observations with the largest optical telescopes on Earth. This led to the measurement of the redshift of this GRB, which turned out to be well 2.4.

Even AGILE observed the GRB 131108A (GCN 15479, Giuliani et al.) That is “passed” in the field of view of the instrument during The GRID first 150 seconds after the event, during which he showed an issue much longer than to that observed in hard X- band. This GRB spectrum showed a very “soft” band, which has allowed AGILE, which is optimized to work at lower energies compared to Fermi, to reveal a significant number of photons in the band (that between 10 and 100 MeV) in which it is traditionally difficult to astronomy and that is still largely unexplored.

To make it even more interesting the event on November 8, is the considerable distance from which the gamma photons of the GRB. The brightness and the distance of this event imply that the energy released in a few seconds from the GRB 131108A is 1000 times greater than that produced by the Sun during its entire life.

In the following hours and days they were observed by observers divesting the afterglow in optical, in radio and in X-rays, providing a formidable set of data for the study of multi-wavelength GRB.

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