TITLE: GCN CIRCULAR NUMBER: 15926 SUBJECT: GRB 140304A: Swift-XRT refined Analysis DATE: 14/03/05 02:57:04 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), J.A. Kennea (PSU), V. Mangano (PSU), M.C. Stroh (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 140304A (Evans et al. GCN Circ. 15915), from 81 s to 23.1 ks after the BAT trigger. The data comprise 42 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 15925). The late-time light curve (from T0+5.2 ks) is consistent with a constant source of mean count rate 1.1e+00 ct/sec. A power-law fit gives an index of 0.2 (+/-0.7). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.00 (+0.15, -0.14). The best-fitting absorption column is 9.8 (+3.4, -3.1) x 10^20 cm^-2, in excess of the Galactic value of 6.0 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.8 (+3.4, -3.1) x 10^20 cm^-2 Galactic foreground: 6.0 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 2.00 (+0.15, -0.14) If the light curve continues to decay with a power-law decay index of 0.2, the count rate at T+24 hours will be 0.024 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.7 x 10^-13 (1.1 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/00590206. This circular is an official product of the Swift-XRT team.