A. Rouco Escorial, W. Fong, C. D. Kilpatrick, J. Rastinejad, G. Schroeder, A. Nugent (Northwestern), E. Berger (Harvard), and T. Laskar (Radboud) report:
���We initiated our afterglow monitoring campaign, consisting of two EPIC-pn observations, with the XMM-Newton Observatory on the short-duration GRB 211106A (Tohuvavohu et al., GCN #31049) on 2021 November 20 (22:37:51 UT) and 2021 December 8 (19:46:37 UT) UT, with median observation times of ~15 and ~33 days post-trigger. The two XMM-Newton observations were obtained under the Proposal 086286 (PI: Fong), with effective exposure times of ~20 ks and ~47 ks, respectively.
In the combined XMM-Newton dataset, we detect the X-ray counterpart to GRB 211106A at the position:
RA(J2000) = 22h54m20.8s
Dec(J2000) = -53d13m50.9s
with a total positional uncertainty of 1.7 arcsec (dominated by XMM-Newton���s systematic uncertainty). The XMM-Newton position of the X-ray afterglow and the Chandra position reported by Berger et al. (2021, GCN #31145) are consistent with each other within the errors. The afterglow is detected in both epochs at a significance of ~5.5 sigma and ~3.4 sigma, with total net source counts of ~83 and ~73 (0.3-10 keV), respectively.
The XRT, Chandra and XMM-Newton afterglow unabsorbed flux, starting at ~0.5 days post-burst, can be modeled with a single power-law decline characterized by a decay index (F~t^alpha) of alpha=-1.02 (-0.06,+0.05). Additionally, from our jointly spectral fitting of both data sets, we derive an intrinsic neutral hydrogen absorption column of ~1.4E21 cm^2 for z=0.097 (Malasani et al., GCN #31075; Christensen et al., GCN #31075). We obtain higher inferred intrinsic column density for greater presumed source redshifts (Kilpatrick et al., GCNs #31146, #31157).
We thank the XMM-Newton Project Scientist, Norbert Shartel, and staff for the rapid planning and scheduling of these observations.���