GCN Circular 10201

P.A. Evans, K.L. Page (U. Leicester) and E. Troja (NASA/GSFC/ORAU) report on
behalf of the Swift-XRT team:

We have analysed 2.4 ks of XRT data for GRB 091127 (Troja et al. GCN
Circ. 10191
Loading...
 
 ), from 3.2 ks to 15.8 ks after the BAT trigger. The data
comprise 761 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. Using 1066 s of PC mode data and 4 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 = 36.58290,
-18.95250 which is equivalent to:

RA (J2000): 02 26 19.89
Dec(J2000): -18 57 08.9

with an uncertainty of 1.4 arcsec (radius, 90% confidence). This is
consistent with the optical/UV/IR position reported in GCN Circs
10192
Loading...
 
 -4.

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.09 (+/-0.05).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.97 (+/-0.08). The
best-fitting absorption column is 7.9 (+1.7, -1.6) x 10^20 cm^-2, in
excess of the Galactic value of 2.8 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.98 (+0.15, -0.14)
and a best-fitting absorption column of 9.8 (+3.3, -3.1) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.9 x 10^-11 (4.9 x 10^-11) erg cm^-2
count^-1.

If the light curve continues to decay with a power-law decay index of
1.09, the count rate at T+24 hours will be 0.24 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.3 x
10^-12 (1.2 x 10^-11) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00377179.

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