GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?

TL;DR

This paper analyzes GRB970228 and a proposed new class of GRBs with initial spikes and softer extended emission, showing they do not follow the Amati relation and are characterized by low-density environments, challenging existing correlations.

Contribution

It introduces a theoretical framework explaining why this new class of GRBs deviates from the Amati relation within the fireshell model.

Findings

GRB970228 and similar GRBs do not follow the Amati relation.

These GRBs occur in low-density galactic environments, possibly in the halo.

The fireshell model explains the absence of the Amati correlation for this class.

Abstract

On the basis of the recent understanding of GRB050315 and GRB060218, we return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow. We proposed it as the prototype for a new class of GRBs with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". Detailed theoretical computation of the GRB970228 light curves in selected energy bands for the prompt emission are presented and compared with observational BeppoSAX data. From our analysis we conclude that GRB970228 and likely the ones of the above mentioned new class of GRBs are "canonical GRBs" have only one peculiarity: they exploded in a galactic environment, possibly the halo, with a very low value of CBM density. Here we investigate how GRB970228 unveils another peculiarity of this class of GRBs: they do not fulfill the "Amati relation". We provide a theoretical explanation within the fireshell model for the apparent absence of such correlation for the GRBs belonging to this new class.