The puzzling clustering and bimodality of long GRBs optical afterglow luminosities

TL;DR

This paper investigates the intrinsic optical afterglow luminosities of long GRBs, revealing unexpected clustering and bimodality that suggest underlying physical differences and provide insights into optically dark GRBs.

Contribution

It demonstrates that the observed luminosity patterns are intrinsic and not due to selection effects, offering new understanding of GRB afterglow emission.

Findings

Clustering of optical luminosities at 12h post-trigger

Evidence of bimodality in luminosity distribution

Implications for the nature of optically dark GRBs

Abstract

The study of the rest frame properties of long Gamma-Ray bursts (GRBs) afterglows is a fundamental aspect for a better understanding of the nature of these powerful explosions. The launch of the Swift satellite (November 2004) marked a strong improvement of the observational capabilities of X-rays and optical afterglows. We studied the intrinsic optical afterglows of a sample of long GRBs finding an unexpected clustering and a hint of bimodality of the optical luminosity distribution (at 12h after the trigger). Through a Montecarlo simulation we proved that both the observed clustering and bimodality are not simply due to selection effects but should hide important information in the understanding of the nature of the afterglow emission. These findings can shed also light on the nature of the large fraction of optically dark GRBs.