Expansion and Spectral Softening of the Dust-scattering Rings of GRB 221009A

An expanding X-ray halo or rings appear when short pulses of X-ray radiation from a background source are scattered by clouds of dust in the Milky Way. We study the X-ray rings of the brightest gamma-ray burst (GRB) 221009A, detected by the Swift X-Ray Telescope. The rings center on the GRB position...

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Bibliographic Details
Published in:The Astrophysical journal 2024-08, Vol.970 (2), p.124
Main Authors: Zhao, Guoying, Shen, Rong-Feng
Format: Article
Language:English
Subjects:
Angular position
Dust
Fluence
Gamma ray bursts
Gamma rays
Milky Way
Scattering
Short pulses
Softening
Spectral analysis
Spectrum analysis
Time dependence
X ray telescopes
X-rays
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Summary:An expanding X-ray halo or rings appear when short pulses of X-ray radiation from a background source are scattered by clouds of dust in the Milky Way. We study the X-ray rings of the brightest gamma-ray burst (GRB) 221009A, detected by the Swift X-Ray Telescope. The rings center on the GRB position, and their angular radii increase with time. We identify five major expanding rings, and our modeling of their expansion history suggests that they are scattered off from five dusty clouds at distances of 0.4–13 kpc from the observer. Given an assumed prompt X-ray fluence of this GRB, the fluxes of those rings suggest that these clouds have dust grain column densities of 10 7∼8 cm −2 . More interestingly, our time-dependent spectral analysis of these rings shows that they all experience spectral softening, i.e., getting softer as they expand, with spectral indices ranging from 2.2 to 5, consistent with what the dust-scattering model predicts.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ad5a85