V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows
(PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), O.M.
Littlejohns (U. Leicester) and M. Stamatikos report on behalf of the
We have analysed 9.9 ks of XRT data for GRB 120312A (Stamatikos et al.
GCN Circ. 13049), from 112 s to 19.6 ks after the BAT trigger. The
data are entirely in Photon Counting (PC) mode. Using 2188 s of PC mode
data and 2 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 = 251.78816, +23.85817 which is equivalent to:
RA (J2000): 16h 47m 09.16s
Dec(J2000): +23d 51' 29.4"
with an uncertainty of 1.6 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.28 (+0.14, -0.13).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.54 (+0.26, -0.25). The
best-fitting absorption column is 1.4 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 4.1 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 4.9 x 10^-11 (5.7 x 10^-11) erg
A summary of the PC-mode spectrum is thus:
Total column: 1.4 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 4.1 x 10^20 cm^-2
Excess significance: 2.1 sigma
Photon index: 1.54 (+0.26, -0.25)
The results of the XRT-team automatic analysis are available at
This circular is an official product of the Swift-XRT team.