[vsnet-grb-info 14570] iPTF14yb: Swift-XRT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15884
SUBJECT: iPTF14yb: Swift-XRT detection
DATE:    14/02/27 09:26:21 GMT
FROM:    Andy Beardmore at U Leicester  <ab271 at leicester.ac.uk>

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.