Magnetar Giant Flares Masquerading as Gamma-Ray Bursts

Magnetars are slowly-rotating neutron stars with extremely strong magnetic fields (10^13-15 G), episodically emitting 100 ms long X-ray bursts with energies of about 10^40-41 erg. Rarely, they produce extremely bright, energetic giant flares that begin with a short (200 ms) intense flash, followed by fainter emission lasting several minutes that is modulated by the magnetar spin period (typically 2-12 s), thus confirming their origin. Over the last 40 years, only three such flares have been observed within our local galactic group, which all suffered from instrumental saturation due to their extreme intensity. It has been proposed, that extragalactic giant flares likely constitute a subset of short gamma-ray bursts, noting that the sensitivity of current instrumentation prevents us from detecting the pulsating tail to distances slightly beyond the Magellanic clouds. However, their initial bright flash is readily observable out to distances of < 60 Mpc. In this talk, X- and gamma-ray observations of bright transient called “GRB200415A”, will be presented. We evaluate the spectral and temporal behavior of this event, which provide tantalizing clues as to the nature of the source. The implications of this work for future studies of these high-energy studies, will also be provided.