Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
Introducing Einstein Probe, Astro Flavored Markdown, and Notices Schema v4.0.0. See news and announcements

GCN Circular 13892

GRB 121024A: Swift-XRT refined Analysis
2012-10-24T19:24:10Z (12 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.
Looking for U.S. government information and services? Visit