The power of the rings: the GRB 221009A soft X-ray emission from its dust-scattering halo

TL;DR

This study analyzes the dust-scattering X-ray rings from the exceptionally bright GRB 221009A to reconstruct its prompt emission spectrum and estimate its fluence, revealing insights into dust properties and the burst's energy output.

Contribution

It provides the first detailed analysis of dust-scattering halos from GRB 221009A, reconstructing the prompt X-ray spectrum and constraining the burst's fluence considering dust uncertainties.

Findings

Reconstructed the GRB's prompt emission spectrum as an absorbed power law.

Constrained the GRB fluence between 1E-3 and 7E-3 erg/cm^2.

Detected and analyzed 20 dust-scattering rings at various distances.

Abstract

GRB 221009A is the brightest gamma-ray burst (GRB) ever detected and occurred at low Galactic latitude. Owing to this exceptional combination, its prompt X-ray emission could be detected for weeks in the form of expanding X-ray rings produced by scattering in Galactic dust clouds. We report on the analysis of 20 rings, generated by dust at distances ranging from 0.3 to 18.6 kpc, detected during two XMM-Newton observations performed about 2 and 5 days after the GRB. By fitting the spectra of the rings with different models for the dust composition and grain size distribution, we reconstructed the spectrum of the GRB prompt emission in the 0.7-4 keV energy range as an absorbed power law with photon index 1-1.4 and absorption in the host galaxy nHz=(4.1-5.3)E21 cm-2. Taking into account the systematic uncertainties on the column density of dust contained in the clouds producing the rings, the 0.5-5 keV fluence of GRB 221009A can be constrained between 1E-3 and 7E-3 erg cm-2.