M. Capalbi, M. Perri (ASDC), P. Romano, A. Moretti, C. Pagani, G.
Tagliaferri (INAF-OAB), D. Malesani (SISSA), D. N. Burrows, J. Kennea, D.
Grupe (PSU), K. Page, M. Goad, A. Beardmore (U. Leicester), V. La Parola,
T. Mineo (IASF/Palermo), N. Gehrels (NASA/GSFC), and S. Kobayashi (PSU)
report on behalf of the Swift XRT team:
We have analyzed the Swift XRT data from the first orbit observation
of GRB 050406 (Parsons et al., GCN3180; Cusumano et al., GCN 3186). The
new refined coordinates are:
RA(J2000) = 2h 17m 52.64s
Dec(J2000) = -50:11:18.80
This position is 28 arcseconds from the refined BAT position given in GCN
3183 (Krimm et al. 2005). We estimate an uncertainty of 5 arcseconds
radius (90% containment).
This is 30 arcsec from the refined BAT position (Krimm et al., GCN
3183) and 3.2 arcsec from the preliminary XRT position (GCN 3186).
The [0.2-10] keV light curve in Windowed Timing (WT) and Photon Counting
(PC) mode starts 106 seconds from the BAT trigger (T0). At the beginning,
the count rate is rapidly rising, peaking at about 218 seconds from T0.
Then it decays very fast, possibly flattening at T-T0=300 seconds.
A preliminary spectral fit to the WT data gives a spectral power law photon
index of 2.1 � 0.3 in the [0.5-10] keV band, assuming Galactic absorption
(3.3E20cm^-2). The average (in the time range 100-700 seconds from
trigger) estimated unabsorbed 0.5-10 keV flux is then about 2.8E-11 erg