GCN Circular 15968

L. Izzo (URoma/ICRA), V. D'Elia (ASDC) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 140311A (Racusin  et al.
GCN Circ. 15944
Not found
 
 
),  from 9.5 ks to 57.1 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. Using 2850 s of PC mode
data and 7 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 = 209.30521, +0.64191 which is equivalent to:

RA (J2000): 13h 57m 13.25s
Dec(J2000): +00d 38' 30.9"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.13 (+0.16, -0.14).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.61 (+0.17, -0.12). The
best-fitting absorption column is  consistent with the Galactic value
of 2.8 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 3.9 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 2.8 x 10^20 cm^-2
Intrinsic column:    0 (+2.2, -0) x 10^22 cm^-2 at z=4.95
Photon index:	     1.61 (+0.17, -0.12)

If the light curve continues to decay with a power-law decay index of
1.13, the count rate at T+24 hours will be 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.1 x
10^-13 (5.3 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00591390

This circular is an official product of the Swift-XRT team.