GCN Circular 9543
Subject
GRB 090621: Swift-XRT Team refined analysis
Date
2009-06-21T12:18:05Z (15 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page (U. Leicester) & P.A. Curran (UCL-MSSL) report on behalf of the
Swift-XRT team:
We have analysed the first four orbits of XRT data obtained for GRB
090621 (Curran et al., GCN Circ. 9540), comprising 192 s of Windowed
Timing (WT) mode and 6.4 ks of Photon Counting (PC) mode. The refined XRT
position is RA, Dec = 11.01982, 61.94115, which is equivalent to
RA (J2000) = 00 44 04.76
Dec(J2000) = +61 56 28.1
with an uncertainty of 3.6 arcsec (radius, 90% containment).
The X-ray light-curve shows a large increase in emission peaking at 264 s
after the initial trigger, corresponding to the time of the second BAT
trigger (Curran et al., GCN Circ. 9540). The underlying decay, however,
can be parameterised as a single power-law with alpha = 0.81 +/- 0.04.
As is common, there is clear spectral evolution during the flare. A
spectrum extracted from the PC mode data after the flare subsides (500 s
after the trigger) can be modelled with a power-law of Gamma = 2.07
+0.37/-0.35 and a total absorbing column of (1.5 +/- 0.4)x10^22 cm^-2; the
Galactic column in this direction is 5.6x10^21 cm^-2 (Kalberla et al.
2005). Using this spectrum, the counts to observed (unabsorbed) flux
conversion factor is 6.3x10^-11 (1.5x10^-10) erg cm^-2 count^-1.
If the light-curve continues to decay with alpha ~ 0.81, the predicted
count rate at 24 hours is 0.015 count s^-1, corresponding to an observed
(unabsorbed) flux of 9.5x10^-13 (2.2x10^-12) erg cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.