TITLE: GCN CIRCULAR NUMBER: 22707 SUBJECT: GRB 180510A: Swift-XRT refined Analysis DATE: 18/05/11 19:47:04 GMT FROM: Phil Evans at U of Leicester A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB) and J.D. Gropp report on behalf of the Swift-XRT team: We have analysed 4.9 ks of XRT data for GRB 180510A (Gropp et al. GCN Circ. 22695), from 77 s to 40.5 ks after the BAT trigger. The data comprise 228 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 276.3314, -31.9081 which is equivalent to: RA (J2000): 18 25 19.54 Dec(J2000): -31 54 29.1 with an uncertainty of 3.6 arcsec (radius, 90% confidence). The late-time light curve (from T0+15.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.2 (+/-0.4). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.94 (+0.08, -0.07). The best-fitting absorption column is 5.2 (+/-0.5) x 10^21 cm^-2, in excess of the Galactic value of 2.1 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.01 (+0.30, -0.28) and a best-fitting absorption column of 3.5 (+1.4, -1.2) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.5 (+1.4, -1.2) x 10^21 cm^-2 Galactic foreground: 2.1 x 10^21 cm^-2 Excess significance: 1.9 sigma Photon index: 2.01 (+0.30, -0.28) If the light curve continues to decay with a power-law decay index of 1.2, the count rate at T+24 hours will be 0.016 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.2 x 10^-13 (9.4 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/00831810. This circular is an official product of the Swift-XRT team.