http://arxiv.org/abs/2008.10822
Giant flares (GFs) are unusual bursts from soft gamma-ray repeaters (SGRs) that release an enormous amount of energy in a fraction of a second. The afterglow emission of these SGR-GFs or GF candidates is a highly beneficial means of discerning their composition, relativistic speed, and emission mechanisms. GRB 200415A is a recent GF candidate observed in a direction coincident with the nearby Sculptor galaxy at 3.5 Mpc. While GeV emission is yet not observed from the magnetars, here, we constrain the flux in the past 12 years of observations by Fermi in the direction of GRB 200415A. The observations confirm that the GRB 200415A is observed as a transient GeV source. We find that a pure pair-plasma fireball cannot explain the observed energetic photons during afterglow emission. A baryonic poor outflow is additionally required to convert the kinetic energy into radiation energy efficiently. A baryonic rich outflow is also viable, as it can explain the variability and observed quasi-thermal spectrum of the prompt emission if dissipation is happening below the photosphere via internal shocks. Hints of a correlation of the peak energy and isotropic luminosity are present in the time-dependent data. This supports that the $\rm E_p – E_{iso}$ correlation found in SGRs-GFs can be indeed intrinsic to these sources, thus, favoring a baryonic poor outflow, and the variability arising intrinsically from the injection process.
V. Chand, J. Joshi, R. Gupta, et. al.
Wed, 26 Aug 20
-1191/66
Comments: Submitted to ApJL
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