Apr 12 – 17, 2021
Africa/Johannesburg timezone

High-Energy Emission from a Magnetar Giant Flare in the Sculptor Galaxy

Apr 14, 2021, 7:30 PM
Contributed Gamma-ray Bursts Exploring the Cosmos: GRB-1


Niccolo' Di Lalla


Magnetars are neutron stars with the strongest-known magnetic fields in the Universe, up to a thousand times stronger than typical neutron stars. Rarely, magnetars can produce enormous eruptions, called giant flares, consisting of a highly luminous sub-second initial spike of hard X-rays and soft gamma rays, followed by a softer and much dimmer pulsating tale lasting a few hundred seconds.

In this talk, we present the recent discovery of the first GeV emission from a magnetar giant flare (MGF) performed by the Fermi Large Area Telescope (LAT). On April 15 2020, the LAT detected GeV gamma rays in temporal coincidence with GRB 200415A, which was detected at MeV and localized by the InterPlanetary Network (IPN). Our detailed analysis shows that the GeV signal is consistent with the IPN localization and spatially associated with the nearby Sculptor galaxy. Thus, we infer that gamma rays likely originated with the MGF in Sculptor, and not from a from a cosmological gamma-ray burst, and we suggest that the GeV signal is generated by an ultra-relativistic outflow that first radiates the prompt MeV-band photons.

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