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The IXPE view of GRB221009A

Presentation #109.07 in the session IXPE.

Published onJul 01, 2023
The IXPE view of GRB221009A

This poster is meant to complement the presentation about the IXPE observation of GRB 221009A. Here, we provide more details on data analysis and interpretation.

GRB 221009A is an exceptionally bright gamma-ray burst (GRB) that reached Earth on 2022 October 9 after traveling through the dust of the Milky Way. The Imaging X-ray Polarimetry Explorer (IXPE) pointed at GRB 221009A on October 11 to observe, for the first time, the 2-8 keV X-ray polarization of a GRB afterglow. We set an upper limit to the polarization degree of the afterglow emission of 13.8% at a 99% confidence level. This result provides constraints on the jet opening angle and the viewing angle of the GRB, or alternatively, other properties of the emission region. Additionally, IXPE captured halo-rings of dust-scattered photons which are echoes of the GRB prompt emission. The 99% confidence level upper limit of the prompt polarization degree is about 55%, consistent with a scenario involving synchrotron emission in an ordered magnetic field. This single IXPE pointing provides both the first assessment of X-ray polarization of a GRB afterglow and the first GRB study with polarization observations of both the prompt and afterglow phases.

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