TITLE: GCN CIRCULAR NUMBER: 31010 SUBJECT: GRB 211018A: Swift-XRT observations DATE: 21/10/26 20:59:36 GMT FROM: Phil Evans at U of Leicester <pae9@leicester.ac.uk> S. Dichiara (PSU), B. Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (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 211018A (Arimoto et al. GCN Circ. 30943), collecting 4.4 ks of Photon Counting (PC) mode data between T0+304.3 ks and T0+340.2 ks. Five uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. We notice that Source 2 and Source 4 are consistent with catalogued quasars at redshift z = 0.64 and z=1.09, respectively. Details of these sources are given below: Source 1: RA (J2000.0): 19.5986 = 01:18:23.66 Dec (J2000.0): -3.6511 = -03:39:04.1 Error: 6.1 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (2.68 [+1.16, -0.92])e-3 ct s^-1 Distance: 338 arcsec from Fermi/LAT position. Flux: (9.3 [+4.0, -3.2])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 2: RA (J2000.0): 19.5656 = 01:18:15.74 Dec (J2000.0): -3.3800 = -03:22:48.2 Error: 5.1 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (9.6 [+3.9, -3.1])e-3 ct s^-1 Distance: 884 arcsec from Fermi/LAT position. Source 3: RA (J2000.0): 19.4544 = 01:17:49.06 Dec (J2000.0): -3.6662 = -03:39:58.4 Error: 7.2 arcsec (radius, 90% conf.) Count-rate: (3.6 [+1.4, -1.1])e-3 ct s^-1 Distance: 835 arcsec from Fermi/LAT position. Flux: (1.85 [+0.70, -0.56])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 4: RA (J2000.0): 19.5576 = 01:18:13.83 Dec (J2000.0): -3.7295 = -03:43:46.2 Error: 3.2 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (6.6 +/- 1.6)e-3 ct s^-1 Distance: 636 arcsec from Fermi/LAT position. Flux: (1.70 +/- 0.40)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 5: RA (J2000.0): 19.6548 = 01:18:37.16 Dec (J2000.0): -3.6066 = -03:36:23.9 Error: 8.0 arcsec (radius, 90% conf.) Count-rate: (2.46 [+1.08, -0.85])e-3 ct s^-1 Distance: 84 arcsec from Fermi/LAT position. Flux: (5.3 [+2.3, -1.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV) 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/ToO_GRBs/00021463. This circular is an official product of the Swift-XRT team.