TITLE: GCN CIRCULAR NUMBER: 15884 SUBJECT: iPTF14yb: Swift-XRT detection DATE: 14/02/27 09:26:21 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore, P.A. Evans and K.L. Page (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 2.3 ks of XRT data for the PTF-detected transient / possible GRB iPTF14yb, from 24.8 ks to 42.8 ks after the time of the initial PTF observation. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the PTF error circle. The refined XRT position is RA, Dec = 221.49179, +14.99396 which is equivalent to: RA (J2000): 14 45 58.03 Dec(J2000): +14 59 38.3 with an uncertainty of 3.7 arcsec (radius, 90% confidence). This position is 2.9 arcsec from the PTF position. The source has a mean count rate of 4.7e-02 ct/sec and shows marginal evidence for fading at the 1.6-sigma level, with a decay slope of 1.14, however more data are required to confirm this. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.15 (+0.51, -0.30). The best-fitting absorption column is consistent with the Galactic value of 1.5 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 3.3 x 10^-11 (3.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 1.5 x 10^20 cm^-2 Intrinsic column: 0 (+6.2, -0) x 10^21 cm^-2 at z=1.98 Photon index: 2.15 (+0.51, -0.30) The ROSAT (PSPC) All Sky Survey 3-sigma upper limit at the position of this source is 0.056 ct/sec, which, given the spectrum above, corresponds to 0.03 ct/sec in the XRT; hence the source was not seen at the current flux level at the time of the RASS. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00033157. This circular is an official product of the Swift-XRT team.