XMM-Newton and Swift observations prove GRB 090709A to be a distant, standard, long GRB

TL;DR

This study uses XMM-Newton and Swift observations to confirm that GRB 090709A is a distant, typical long gamma-ray burst, despite initial suggestions of unusual periodicity.

Contribution

The paper provides detailed X-ray spectroscopy and re-analysis of prompt emission data to clarify the nature of GRB 090709A, establishing it as a standard long GRB at high redshift.

Findings

GRB 090709A is at redshift z=4.2.

No significant periodicity at 8.1 s was found.

The burst has a large host galaxy column density (~6.5E+22 cm^-2).

Abstract

GRB 090709A is a long gamma-ray burst (GRB) discovered by Swift, featuring a bright X-ray afterglow as well as a faint infrared transient with very red and peculiar colors. The burst attracted a large interest because of a possible quasi-periodicity at P=8.1 s in the prompt emission, suggesting that it could have a different origin with respect to standard, long GRBs. In order to understand the nature of this burst, we obtained a target of opportunity observation with XMM-Newton. X-ray spectroscopy, based on XMM-Newton and Swift data, allowed us to model the significant excess in photoelectric absorption with respect to the Galactic value as due to a large column density (about 6.5E+22 cm^-2) in the GRB host, located at z=4.2. Such a picture is also consistent with the infrared transient's properties. Re-analysis of the prompt emission, based on INTEGRAL and on Swift data, excludes any significant modulation at P=8.1 s. Thus, we conclude that GRB 090709A is a distant, standard, long GRB.