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 16767

GRB 140903A: Swift-XRT refined Analysis
2014-09-03T20:57:43Z (10 years ago)
Massimiliano de Pasquale at IASF-Palermo <>
M. De Pasquale, A. Maselli (IASF-Palermo), J. R. Cummings (NASA/UMBC)
reports on behalf of the Swift-XRT team:

We have analysed 2.9 ks of XRT data for GRB 140903A (Cummings  et al.
GCN Circ. 16763),  from 74 s to 7.3 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. Using 3407 s of PC mode data
and 7 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 = 238.01361, +27.60259 which is equivalent to:

RA (J2000): 15h 52m 03.27s
Dec(J2000): +27d 36' 09.3"

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=0.21 (+/-0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.71 (+0.21, -0.20). The
best-fitting absorption column is  1.2 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 3.3 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.0 x 10^-11 (4.7 x 10^-11) erg
cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:         1.2 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 3.3 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index:         1.71 (+0.21, -0.20)

If the light curve continues to decay with a power-law decay index of
0.21, the count rate at T+24 hours will be 0.11 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x
10^-12 (5.3 x 10^-12) 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