K.L. Page (U. Leicester), C. Pagani (U. Leicester), G. Stratta (ASDC),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), M.C. Stroh (PSU), D.N.
Burrows (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and
P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 10 ks of XRT data for GRB 130315A (Evans et al. GCN
Circ. 14311), from 167 s to 29.4 ks after the BAT trigger. The data
comprise 337 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
157.54687, -51.79362 which is equivalent to:
RA (J2000): 10 30 11.25
Dec(J2000): -51 47 37.0
with an uncertainty of 3.6 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=.
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.49 (+/-0.04). The
best-fitting absorption column is 2.88 (+0.19, -0.18) x 10^21 cm^-2,
in excess of the Galactic value of 2.3 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.1 (+/-0.3) and a
best-fitting absorption column of 3.1 (+1.2, -0.8) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.9 x 10^-11 (6.7 x 10^-11) erg cm^-2
A summary of the PC-mode spectrum is thus:
Total column: 3.1 (+1.2, -0.8) x 10^21 cm^-2
Galactic foreground: 2.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.1 (+/-0.3)
The results of the XRT-team automatic analysis are available at
This circular is an official product of the Swift-XRT team.