GRB 210217A: a short or a long GRB?

Abstract

Gamma-ray bursts are traditionally classified as short and long bursts based on their T90 value (the time interval during which an instrument observes 5% to 95% of gamma-ray/hard X-ray fluence). However, T90 is dependent on the detector sensitivity and the energy range in which the instrument operates. As a result, different instruments provide different values of T90 for a burst. GRB 210217A is detected with different duration by Swift and Fermi. It is classified as a long/soft GRB by Swift-BAT with a T90 value of 3.76 s. On the other hand, the sub-threshold detection by Fermi-GBM classified GRB 210217A as a short/ hard burst with a duration of 1.024 s. We present the multi-wavelength analysis of GRB 210217A (lying in the overlapping regime of long and short GRBs) to identify its actual class using multi-wavelength data. We utilized the T90-hardness ratio, T90 Ep and T90 tmvts distributions of the GRBs to find the probability of GRB 210217A being a short GRB. Further, we estimated the photometric redshift of the burst by fitting the joint XRT/UVOT SED and placed the burst in the Amati plane. We found that GRB 210217A is an ambiguous burst showing properties of both short and long class of GRBs.