TITLE: GCN CIRCULAR NUMBER: 32135 SUBJECT: GRB 220527A: Swift-XRT afterglow detection DATE: 22/05/28 01:10:03 GMT FROM: Phil Evans at U of Leicester B. Sbarufatti (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , D.N. Burrows (PSU), J. D. Gropp (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 220527A (Bissaldi et al. GCN Circ. 32131), collecting 1.7 ks of Photon Counting (PC) mode data between T0+30.1 ks and T0+31.9 ks. Two uncatalogued X-ray sources are detected, of which one ("Source 2") is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1733 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 323.52805, -14.97183 which is equivalent to: RA (J2000): 21h 34m 06.73s Dec(J2000): 14d 58' 18.6" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is 4.9 arcmin from the Fermi/LAT position. The light curve is consistent with a constant source of mean count rate 3.9e-01 ct/sec. A power-law fit gives an index of 0.6 (+2.5, -1.1). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.83 (+0.21, -0.20). The best-fitting absorption column is 9.8 (+6.1, -3.5) x 10^20 cm^-2, consistent with the Galactic value of 6.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.8 (+6.1, -3.5) x 10^20 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.83 (+0.21, -0.20) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021503. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021503. This circular is an official product of the Swift-XRT team.