TITLE: GCN CIRCULAR NUMBER: 23236 SUBJECT: GRB 180914B: Swift-XRT afterglow detection DATE: 18/09/15 22:21:41 GMT FROM: Paolo D'Avanzo at INAF-OAB A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), S.L. Gibson (U. Leicester), Z. Liu (NAOC / U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 180914B (Bissaldi et al. GCN Circ. 23232) in a series of observations tiled on the sky. The total exposure time is 4.1 ks, distributed over 6 tiles; the maximum exposure at a single sky location was 1.3 ks. The data were collected between T0+82.8 ks and T0+93.8 ks, and are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected and is above the RASS limit, and is therefore likely the GRB afterglow. Using 579 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 = 332.35648, +25.06314 which is equivalent to: RA (J2000): 22h 09m 25.56s Dec(J2000): +25d 03' 47.3" with an uncertainty of 3.4 arcsec (radius, 90% confidence). This position is 12.1 arcmin from the Fermi/LAT position. The source has a mean count rate of 6.2e-02 ct/sec; we cannot determine at the present time whether it is fading. The results of the XRT-team automatic analysis of the likely afterglow are at http://www.swift.ac.uk/xrt_products/TILED_GRB00075/Source2.php. The results of the full analysis of the tiled XRT observations are available at http://www.swift.ac.uk/xrt_products/TILED_GRB00075. This circular is an official product of the Swift-XRT team.