TITLE: GCN CIRCULAR NUMBER: 22830 SUBJECT: GRB 180623A: Swift-XRT refined Analysis DATE: 18/06/23 23:56:06 GMT FROM: Phil Evans at U of Leicester J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA) and K.L. Page report on behalf of the Swift-XRT team: We have analysed 7.7 ks of XRT data for GRB 180623A (Page et al. GCN Circ. 22828), from 83 s to 18.2 ks after the BAT trigger. The data comprise 90 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 22829). The late-time light curve (from T0+4.5 ks) can be modelled with a power-law decay with a decay index of alpha=1.72 (+/-0.14). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.73 (+0.20, -0.19). The best-fitting absorption column is 6.4 (+/-0.7) x 10^22 cm^-2, in excess of the Galactic value of 1.5 x 10^22 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.04 (+0.27, -0.25) and a best-fitting absorption column of 6.6 (+/-0.9) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 9.0 x 10^-11 (2.9 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.6 (+/-0.9) x 10^22 cm^-2 Galactic foreground: 1.5 x 10^22 cm^-2 Excess significance: 9.9 sigma Photon index: 2.04 (+0.27, -0.25) If the light curve continues to decay with a power-law decay index of 1.72, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x 10^-13 (6.5 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/00844015. This circular is an official product of the Swift-XRT team.