GCN Circular 32571
Swift-XRT has performed follow-up observations of the Fermi-LAT-detected burst GRB 220921A, collecting 4.1 ks of Photon Counting (PC) mode data between T0+27.4 and T0+40.7 ks. An uncatalogued X-ray source has been detected consistent with being within 17.3 arcmin from the center of the Fermi-LAT position (which is within its 90% error radius of 25.19 arcmin; Pillera et al., GCN 32568), and being consistent with the optical transient detected by MASTER (Lipunov et al., GCN 32570). The source's peak flux (8.6 (+/- 1.9) * 10^-12 erg cm^-2 s^-1) is 7.6-�� above the RASS limit, and it is fading with 2.9-�� significance. Source 1: RA (J2000.0): 66.47255 = 04:25:53.41 Dec (J2000.0): -40.4057 = -40:24:20.4 Error: 3.8 arcsec (radius, 90% conf.) Count-rate: (0.20 [+/- 0.04]) ct s^-1 Distance: 17.3 arcsec from Fermi-LAT position Exposure: 1328 s (vignetting corrected) Two other uncatalogued sources were also detected within the GRB position. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00107/. Further observations are pending. This circular is an official product of the Swift-XRT team.