TITLE: GCN CIRCULAR NUMBER: 16451 SUBJECT: GRB 140623A: Swift-XRT and UVOT observations DATE: 14/06/24 15:21:15 GMT FROM: Valerio D'Elia at ASDC V. D'Elia (ASDC), F. E. Marshall (NASA/GSFC), L. Izzo (URoma/ICRA) & D. Malesani (DARK/NBI) report on behalf of the Swift team: Following the report of a potential optical afterglow iPTF14cyb (Bhalerao et al., GCN Circ. 16442) to the Fermi/GBM-detected burst GRB 140623A (von Kienlin, GCN Circ. 16450), Swift began a follow-up observation of the iPTF field. We have analyzed all the 3.0 ks of XRT data for GRB 140623A, from 38.7 ks to 49.6 ks after the Fermi/GBM trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected at a position consistent with the candidate optical afterglow (Bhalerao et al., GCN Circ. 16442) within the Fermi/GBM error circle. Using 1153 s of PC mode data and 1 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 = 225.47927, +81.19049 which is equivalent to: RA (J2000): 15h 01m 55.02s Dec(J2000): +81d 11' 25.7" with an uncertainty of 5.8 arcsec (radius, 90% confidence). This position is 5.0 arcsec from the the optical counterpart iPTF14cyb, and consistent with it. We cannot determine at the present time whether the source is fading. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020388. The Swift/UVOT began settled observations of the field of GRB 140423A 38708 s after the GBM trigger. No optical afterglow consistent with the optical position (Bhalerao et al. GCN Circ. 16442) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag u 38708 44173 925 >22.0 white 38926 44863 851 >21.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.037 in the direction of the burst (Schlegel et al. 1998). This circular is an official product of the Swift team.