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GCN Circular 9172

Subject
GRB 090419: Swift-XRT refined analysis
Date
2009-04-20T15:19:33Z (15 years ago)
From
Matteo Perri at ISAC/ASDC <perri@asdc.asi.it>
G. Stratta and M. Perri (ASDC) report on behalf of the
Swift-XRT Team:

We have analysed the first 4 orbits of Swift-XRT data obtained from
GRB 090419 (trigger 349592; Stratta, et al., GCN Circ. 9161),
from T+128 s to T+271 s in Windowed Timing (WT) mode and from
T+303 s to T+4.9 h in Photon Counting (PC) mode.

The best position of the X-ray afterglow is the UVOT enhanced XRT
position given in Osborne et al. (GCN Circ. 9164).

The 0.3-10 keV X-ray light curve shows an initial flaring activity
superimposed to a constant continuum at a level of ~5 counts/s
up to ~520 s after the trigger that is consistent with being
the X-ray tail of the BAT data (GCN Circ. 9167, Krimm et al.) during
the prompt emission.

Starting from 520 s up to 1200 s the count rate decays as
a power law with alpha1=3.5+/-0.5 and from T+1200
to T+12 ks it features a flattening with index alpha2=1.1+/-0.2.
If decaying at this rate, the afterglow will reach a count-rate of
1.3(0.6)E-3 counts/s at T+24(48)h.

The average WT spectrum (corresponding to the initial flat decay phase)
can be fitted by an absorbed power-law model (reduced chi square 1.0 with
18 degrees of freedom), with photon index 1.3+/-0.3, and equivalent
hydrogen column density NH=(1.1+/-0.6)E22 cm-2 in excess with
respect to the Galactic absorption value of 1.2E21 cm-2 (Kalberla et al.
2005). The average observed(unabsorbed) flux in the 0.3-10 keV band is
4.2(5.4)E-10 ergs cm-2 s-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00349510.

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