TITLE: GCN CIRCULAR NUMBER: 30994 SUBJECT: GRB 211024B: Swift-XRT refined Analysis DATE: 21/10/25 15:12:58 GMT FROM: Phil Evans at U of Leicester <pae9@leicester.ac.uk> P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), K.L. Page (U. Leicester) and J.D. Gropp report on behalf of the Swift-XRT team: We have analysed 6.2 ks of XRT data for GRB 211024B (Gropp et al. GCN Circ. 30980), from 105 s to 24.7 ks after the BAT trigger. The data comprise 6 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. Using 6214 s of PC mode data and 12 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 154.71268, +24.56825 which is equivalent to: RA (J2000): 10h 18m 51.04s Dec(J2000): +24d 34' 05.7" with an uncertainty of 1.9 arcsec (radius, 90% confidence). The late-time light curve (from T0+5.6 ks) can be modelled with a power-law decay with a decay index of alpha=2.69 (+0.13, -0.12). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.08 (+0.11, -0.10). The best-fitting absorption column is 9.7 (+2.7, -2.5) x 10^20 cm^-2, in excess of the Galactic value of 2.1 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 3.2 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.7 (+2.7, -2.5) x 10^20 cm^-2 Galactic foreground: 2.1 x 10^20 cm^-2 Excess significance: 5.0 sigma Photon index: 2.08 (+0.11, -0.10) If the light curve continues to decay with a power-law decay index of 2.69, the count rate at T+24 hours will be 5.0 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x 10^-13 (2.0 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01081073. This circular is an official product of the Swift-XRT team.