[vsnet-grb-info 5946] GRB 080411: Swift-XRT Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7590
SUBJECT: GRB 080411: Swift-XRT Refined Analysis 
DATE:    08/04/12 13:27:11 GMT
FROM:    Olivier Godet at U.of Leicester  <og19 at star.le.ac.uk>

O. Godet, A. P. Beardmore, K. Page (U. Leicester) reports on behalf the Swift-XRT team: 

The XRT began observing the field of GRB 080411 (trigger=309010, Marshall et
al., GCN Circ. 7584) at 21:16:42 UT, 71 seconds after the BAT trigger.  We
analysed the first orbit of WT data (0.9 s) at T0+209s and the first 4 orbits
of PC data (~3.6 ks) from T0+4.2ks to T0+17.4ks.

The X-ray light-curve shows a broken power-law behaviour. Since there are 
no data between the WT and PC observations, it is difficult to constrain 
the initial decay and break time. The late decay from the PC data gives a 
decay slope of 0.98+/-0.05. Using ground data, we confirmed that the initial 
intense flux reported by Marshall et al. (GCN Circ. 7584) from the 0.1s image 
taken at T0+71s is real and is likely to correspond to the end of the activity 
observed in the BAT. That implies an initial rapid decay in the XRT light-curve.

The WT spectrum contains only 20 counts. So, the fitting parameters are not
well constrained when the spectrum is fitted by an absorbed power-law (N_H <
4.6e21 cm^-2 in excess with respect to the Galactic absorption along the burst
line of sight (5.7e20 cm^-2, Kalberla et al. 2005) and a photon index of 2.85
+1.54/-1.05).  The PC spectrum from T0+4.2ks to T0_17.4ks is fitted well by 
an absorbed power-law with a photon index of 2.14 +/- 0.09 and an absorption 
column of (1.5 +/- 0.3)e21 cm^-2, in excess with respect to the Galactic one.

The observed (unabsorbed) flux in the 0.3-10 keV band is 7.1e-10 (1.7e-9) erg
cm^-2 s^-1 for the WT spectrum and 7.2e-11 (1.1e-10) erg cm^-2 s^-1 for the PC
spectrum.

The predicted XRT count rate at T0+1d (T0+3d) is 0.26 (0.07) count s^-1, which
corresponds to an observed 0.3-10 keV flux of 2.7e-11 (7.1e-12) erg cm^-2 s^-1.

This is an official product of the Swift-XRT team.