Dust-scattered X-ray halos around two Swift gamma-ray bursts: GRB 061019 and GRB 070129

TL;DR

This paper reports the detection and analysis of two new dust-scattered X-ray halos around GRBs, expanding the sample and providing distance measurements to the scattering dust, demonstrating the effectiveness of a sensitive analysis method.

Contribution

It introduces a refined analysis method for faint X-ray halos around GRBs and measures the distance to the dust responsible for one of the halos.

Findings

Identified a known molecular cloud at 940±40 pc as the scattering dust for GRB 061019.

Detected a second faint halo around GRB 070129, but limited photon data prevented detailed dust modeling.

Expanded the number of observed dust scattering halos around GRBs to five.

Abstract

Two new expanding X-ray rings were detected by the Swift XRT instrument during early follow-up observations of GRB 061019 and GRB 070129, increasing to 5 the number of dust scattering X-ray halos observed around GRBs. Although these two halos were particularly faint, a sensitive analysis can be performed that optimizes the method originally developed by Tiengo & Mereghetti (2006) to analyze dust scattering rings observed with XMM-Newton for the Swift satellite. In the case of GRB 061019, a known giant molecular cloud is identified as the one responsible for the scattering process, and its distance is accurately measured (d=940$\pm$40 pc) through the dynamics of the expanding ring. In the second case, XRT observed both the main peak of the prompt emission of GRB 070129 and the scattering halo, but the small number of detected halo photons prevents us from distinguish between different dust models.