GRB 221009A: IXPE preliminary upper limits of X-ray polarization

IXPE performed the first observation of X-ray polarization of a GRBafterglow in the 2 - 8 keV energy range. IXPE observed GRB 221009A from 2022-10-11T23:34:28UTC to 2022-10-14T00:45:31UTC for an effective exposure of 100 ks. From a quick-look analysis of the image-, time- and energy- averaged low-level instrument data (prior to pipeline processing at the IXPE SOC), we report:Polarization degree (PD) < 11.1% upper limits are derived with 99% C.L.These results are preliminary.The IXPE Collaboration will report the final results in a forthcoming publication. The Imaging X-ray Polarimetry Explorer, commonly known as IXPE is a space observatory with three identical telescopes designed to measure the polarization of cosmic X-rays. X-ray polarimetry enabled by IXPE can be performed in energy-, time-, and angle-resolved fashions. The observatory, which was launched on 9 December 2021, is an international collaboration between NASA and the Italian Space Agency (ASI).