GRB 241105A—The Most Distant Short Gamma-Ray Burst?

Abstract

This paper is devoted to a detailed study of the prompt gamma-ray emission from GRB 241105A based on data from the GBM/Fermi, SPI-ACS/INTEGRAL, Konus–Wind, and BAT/Swift instruments and its X-ray and optical afterglow light curves obtained by various observatories. A bright short main episode followed by a longer and less intense emission can be distinguished in the prompt emission light curve, which is a characteristic feature of short (Type I) bursts with extended emission. A spectral analysis has shown that the main burst episode has a hard energy spectrum typical for short bursts. The extended emission spectrum can be described by a power law with a photon index \(\gamma={-}1.6\pm 0.2\) in the energy range up to a few MeV, making it the hardest extended emission among the observed short bursts. In addition, on the \(E_{p,i}{-}E_{\textrm{iso}}\) and \(T_{90,i}{-}EH\) planes the main episode of GRB 241105A occupies a position typical for short GRBs. At the same time, the X-ray and optical afterglow light curves of GRB 241105A are brightest among the short GRBs (with measured redshifts), which may suggest that the burst belongs to the events connected with the core collapse of massive stars (Type II GRBs). If, however, the hypothesis about the connection of GRB 241105A with the class of short GRBs caused by the mergers of compact objects is valid, then it will be the most distant of the short bursts (the redshift of GRB 241105A is \(z=2.681\)).