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GCN Circular 13892

GRB 121024A: Swift-XRT refined Analysis
2012-10-24T19:24:10Z (11 years ago)
Phil Evans at U of Leicester <>
K.L. Page (U. Leicester), A. Maselli  (INAF-IASFPA), V. Mangano
(INAF-IASFPA), A. Melandri (INAF-OAB), M.C. Stroh (PSU), D.N. Burrows
(PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and C. Pagani
report on behalf of the Swift-XRT team:

We have analysed 7.0 ks of XRT data for GRB 121024A (Pagani  et al. GCN
Circ. 13886), from 82 s to 23.5 ks after the  BAT trigger. The data
comprise 242 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The refined XRT position is RA, Dec = 70.47078, -12.29099 which
is equivalent to:

RA (J2000): 04 41 52.99
Dec(J2000): -12 17 27.6

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The late-time light curve (from T0+3.9 ks) can be modelled with  a
power-law decay with a decay index of alpha=0.89 (+/-0.13).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.15 (+/-0.08). The
best-fitting absorption column is  8.0 (+2.1, -2.0) x 10^21 cm^-2, at a
redshift of 2.298, in addition to the Galactic value of 5.4 x 10^20
cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index
of 1.96 (+/-0.13) and a best-fitting absorption column of 7.1 (+4.0,
-3.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.7 x 10^-11 (4.7
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 5.4 x 10^20 cm^-2
Intrinsic column:    7.1 (+4.0, -3.6) x 10^21 cm^-2 at z=2.298
Photon index:	     1.96 (+/-0.13)

If the light curve continues to decay with a power-law decay index of
0.89, the count rate at T+24 hours will be 0.016 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.8 x
10^-13 (7.3 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at

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