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GCN Circular 13838

Subject
GRB 121001A: Swift-XRT refined Analysis
Date
2012-10-02T12:29:53Z (12 years ago)
From
Valerio D'Elia at ASDC <delia@asdc.asi.it>
V. D'Elia (ASDC) and P. Evans (U. Leicester)  report on behalf of the
Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 121001A (D'Elia et al. GCN
Circ. 13831), from 111 s to 41.8 ks after the  BAT trigger. The data
comprise 93 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 2340 s of PC mode data and 3 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 = 276.03227, -5.66587
which is equivalent to:

RA (J2000): 18h 24m 07.74s
Dec(J2000): -05d 39' 57.1"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.30 (+/-0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.28 (+0.25, -0.24). The
best-fitting absorption column is  7.6 (+2.4, -2.0) x 10^21 cm^-2, in
excess of the Galactic value of 4.5 x 10^21 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 7.6 x 10^-11 (9.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.6 (+2.4, -2.0) x 10^21 cm^-2
Galactic foreground: 4.5 x 10^21 cm^-2
Excess significance: 2.5 sigma
Photon index:	     1.28 (+0.25, -0.24)

If the light curve continues to decay with a power-law decay index of
1.30, the count rate at T+24 hours will be 2.1 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (2.1 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/00535026.

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