GRB241107A: a Giant Flare from a close-by extragalactic Magnetar?

TL;DR

This paper reports on a short gamma-ray burst, likely a giant flare from a nearby extragalactic magnetar, based on precise localization, spectral analysis, and association with a nearby galaxy, challenging the typical short GRB classification.

Contribution

The study provides evidence that GRB 241107A is a giant flare from an extragalactic magnetar, supported by spectral and positional data, expanding understanding of magnetar flares beyond the Milky Way.

Findings

GRB 241107A had a duration of 0.2 seconds and a peak energy of 680 keV.

The burst's isotropic energy is consistent with giant magnetar flares at 4.1 Mpc.

The spectral properties resemble those of known extragalactic magnetar flares.

Abstract

We report the results on the short gamma-ray burst GRB 241107A, obtained with the IBIS instrument on board the INTEGRAL satellite. The burst had a duration of about 0.2 s, a fluence of $8 \times 10^{-7}$ erg cm-2 in the 20 keV-10 MeV range and a hard spectrum, characterized by a peak energy of 680 keV. The position of GRB 241107A has been precisely determined because it fell inside the imaging field of view of the IBIS coded mask instrument. The presence of the nearby galaxy PGC 86046 in the 3 arcmin radius error region, suggests that GRB 241107A might be a giant flare from a magnetar rather than a canonical short GRB. For the 4.1 Mpc distance of PGC 86046, the isotropic energy of $1.6 \times 10^{45}$ erg is in agreement with this hypothesis, that is also supported by the time resolved spectral properties similar to those of the few other extragalactic magnetars giant flares detected so far.