TITLE:   GCN CIRCULAR
NUMBER:  32754
SUBJECT: GRB 221009A: IXPE preliminary upper limits of X-ray polarization 
DATE:    22/10/14 12:58:40 GMT
FROM:    Michela Negro at CRESST/NASA-GSFC/UMBC  <mnegro1@umbc.edu>

Michela Negro, Alberto Manfreda, Nicola Omodei and 
Fabio Muleri report on behalf of the IXPE Collaboration 

IXPE performed the first observation of X-ray polarization of a 
GRB afterglow 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).

[Editor's note: Reformatted at the request of the submitter.]