TITLE: GCN CIRCULAR NUMBER: 36443 SUBJECT: GRB 240511A: Swift-XRT refined Analysis DATE: 24/05/12 08:37:53 GMT FROM: Phil Evans at U of Leicester C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 8.5 ks of XRT data for GRB 240511A, from 94 s to 36.0 ks after the BAT trigger. The data comprise 345 s in Windowed Timing (WT) mode (the first 6 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 336.67568, 8.51317 which is equivalent to: RA (J2000): 22 26 42.16 Dec(J2000): +08 30 47.4 with an uncertainty of 1.9 arcsec (radius, 90% confidence). The late-time light curve (from T0+5.2 ks) can be modelled with a power-law decay with a decay index of alpha=0.76 (+/-0.10). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.07 (+/-0.04). The best-fitting absorption column is 2.60 (+/-0.16) x 10^21 cm^-2, in excess of the Galactic value of 8.5 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.08 (+0.16, -0.15) and a best-fitting absorption column of 1.6 (+0.5, -0.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (4.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.6 (+0.5, -0.4) x 10^21 cm^-2 Galactic foreground: 8.5 x 10^20 cm^-2 Excess significance: 2.8 sigma Photon index: 2.08 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 0.76, the count rate at T+24 hours will be 0.030 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x 10^-12 (1.4 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01227767. This circular is an official product of the Swift-XRT team.