Discovery of a tight correlation for gamma ray burst afterglows with `canonical' light curves

TL;DR

This paper identifies a tight correlation between luminosity and break time in the afterglow light curves of certain gamma-ray bursts, revealing physical subclasses and suggesting progenitor properties influence afterglow brightness.

Contribution

It discovers a new luminosity-break time correlation in canonical GRB afterglows and identifies physical subclasses based on this tight correlation.

Findings

A significant luminosity $L^*_X$ - break time $T^*_a$ correlation in long GRB afterglows.

Existence of a similar relation in intermediate class GRBs.

Brighter afterglows are associated with more regular progenitor explosions.

Abstract

Gamma Ray Bursts (GRB) observed up to redshifts $z>8$ are fascinating objects to study due to their still unexplained relativistic outburst mechanisms and a possible use to test cosmological models. Our analysis of 77 GRB afterglows with known redshifts revealed a physical subsample of long GRBs with canonical {\it plateau breaking to power-law} light curves with a significant {\it luminosity $L^*_X$ - break time $T^*_a$} correlation in the GRB rest frame. This subsample forms approximately the {\it upper envelope} of the studied distribution. We have also found a similar relation for a small sample of GRB afterglows that belong to the intermediate class (IC) between the short and the long ones. It proves that within the full sample of afterglows there exist physical subclasses revealed here by tight correlations of their afterglow properties. The afterglows with regular (`canonical') light curves obey not only a mentioned tight physical scaling, but -- for a given $T^*_a$ -- the more regular progenitor explosions lead to preferentially brighter afterglows.