TITLE: GCN CIRCULAR NUMBER: 45850 SUBJECT: GRB 261007A: Swift-XRT afterglow detection DATE: 26/10/08 07:22:21 GMT FROM: Phil Evans at U of Leicester K.L. Page (U. Leicester), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU), D.N. Burrows (PSU), J.J. DeLaunay (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 261007A, also known as EP261007a (GCN Circ. 45828). We searched for X-ray sources in 1.9 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 1.9 ks, obtained between T0+38.5 ks and T0+44.0 ks. An uncatalogued X-ray source is detected and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. The position of this source is also consistent with the optical counterpart initially discovered by KAIT (GCN Circ. 45825). Using 1918 s of PC mode data and 2 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 = 11.61403, -17.69197 which is equivalent to: RA (J2000): 00h 46m 27.37s Dec(J2000): -17d 41' 31.1" with an uncertainty of 2.7 arcsec (radius, 90% confidence). This position is 2.4 arcmin from the SVOM/ECLAIRs position. The light curve is currently consistent with a constant source of mean count rate 1.3e-01 ct/sec. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.74 (+0.29, -0.21). The best-fitting absorption column is 3.7 (+7.0, -1.6) x 10^20 cm^-2, consistent with 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 3.7 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.7 (+7.0, -1.6) x 10^20 cm^-2 Galactic foreground: 2.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.74 (+0.29, -0.21) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/00021917. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021917. This circular is an official product of the Swift-XRT team.