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GCN Circular 3184

Subject
GRB 050406: early Swift XRT analysis results
Date
2005-04-06T21:45:48Z (19 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
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 
cm^-2 s^-1.
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