GCN Circular 13972

A.P. Beardmore (U. Leicester) and J. R. Cummings (NASA/UMBC) report on
behalf of the Swift-XRT team:

We have analysed 13 ks of XRT data for GRB 121117A (Cummings  et al.
GCN Circ. 13967
Not found
 
 
), from 41 s to 62.7 ks after the  BAT trigger. The data
comprise 204 s in Windowed Timing (WT) mode (the first 5 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 3463 s of PC mode data and 6 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 = 31.61064, +7.41954
which is equivalent to:

RA (J2000): 02h 06m 26.55s
Dec(J2000): +07d 25' 10.4"

with an uncertainty of 1.7 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.27 (+/-0.04).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.55 (+0.22, -0.19). The
best-fitting absorption column is  8.4 (+7.2, -3.2) x 10^20 cm^-2,
consistent with the Galactic value of 5.2 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 4.2 x 10^-11 (4.7 x
10^-11) erg cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     8.4 (+7.2, -3.2) x 10^20 cm^-2
Galactic foreground: 5.2 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.55 (+0.22, -0.19)

If the light curve continues to decay with a power-law decay index of
1.27, the count rate at T+24 hours will be 9.9 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x
10^-14 (4.7 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00538696.

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