Astroparticle Physics Seminar

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


Abstract: The Fermi Gamma-ray Space Telescope has provided unique insights into the Universe’s biggest explosions over the last 12 years.  Gamma-Ray bursts (GRBs) are routinely detected by the two instruments on board the satellite, with thousands of them detected by the Fermi Gamma-ray Burst Monitor (GBM) and hundreds by the Large Area Telescope (LAT). Nevertheless, the transient sky at high energy keeps surprising us: in this seminar, after a brief review of what we have learned studying GRB with the Fermi LAT, I will report on the discovery of GeV emission from a magnetar giant flare (MGF). On April 15, 2020, GeV gamma rays were detected by the LAT after the initial detection of a signal in the MeV band. Our analysis shows that these gamma rays are spatially associated with the nearby (3.5 Mpc) Sculptor galaxy and are unlikely to originate from a cosmological GRB. We infer that the gamma rays originated with the MGF in Sculptor 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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