TITLE:   GCN CIRCULAR
NUMBER:  35163
SUBJECT: GRB 231117A: Chandra afterglow detection
DATE:    23/11/23 03:12:50 GMT
FROM:    Wen-fai Fong at Northwestern University <wfong@northwestern.edu>

W. Fong, T. Eftekhari, G. Schroeder (Northwestern), A. Rouco Escorial (ESA/ESAC) report:

"The Chandra X-ray Observatory observed the position of the short-duration GRB 231117A (Laha et al., GCN 35071, Navaneeth et al., GCN 35072, Cattaneo et al., GCN 35075, Svinkin et al., GCN 35079, Cheung et al., GCN 35081) starting on 2023 November 21 at 06:22:13 UT. We obtained an ACIS-S observation under Proposal 24400307 (PI: Fong), with an effective exposure time of ~27 ksec, for a mid-time of 4.3 days post-burst. 

The X-ray afterglow is clearly detected at high significance. The source is spatially coincident with the optical (e.g., Yang et al., GCN 35083, Rastinejad et al., GCN 35087, Gompertz et al., GCN 35088) and radio (Rhodes et al., GCN 35097, Schroeder et al., GCN 35114) afterglows at the position:

RA (J2000) = 22:09:33.37
Dec (J2000) = 13:31:20.0

We note that, similar to the reported optical positions, the Chandra source is just outside the 90% confidence region of the latest XRT position. We measure a 0.3-10 keV flux for the Chandra afterglow of FX ~ 2e-13 erg/s/cm^2. We find that the XRT light curve beyond ~300 seconds post-burst can be modeled with a single power-law with FX ~ t^-0.6, and that the Chandra observation is fully consistent with this power law.

We thank the Chandra staff for rapid approval and planning of these observations."