[vsnet-grb-info 2038] GRB050824: decay of the XRT light curve and updated X-ray spectrum

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3877
SUBJECT: GRB050824: decay of the XRT light curve and updated X-ray spectrum
DATE:    05/08/25 17:27:22 GMT
FROM:    Sergio Campana at INAF-OAB  <campana at merate.mi.astro.it>

S. Campana (INAF-OAB), A. Moretti (INAF-OAB), V. Mangano (INAF-IASF
Palermo), D.N. Burrows (PSU), report:

We have analyzed 13 ks of Swift XRT data of GRB 050824
(Campana et al., GCN3866).

The 0.2-10 keV light curve XRT (started 6089 seconds after the BAT
trigger) now shows an indication of a temporal decay with a power
law index of -0.4+/-0.2 (90% confidence level).
The power law fit is better than a constant fit at a 3.3 sigma
level (F-test). This indicates that the source suggested in the
previous XRT circular (Campana et al., GCN3872) is the X-ray
afterglow of GRB050724.

The 307 photons in the 0.3-10 keV evergy band were also used for
spectral analysis. We fixed the column density to the Galactic value
(3.6x10^20 cm-2) and added a free local absorption at z=0.83 (Fynbo
et al., GCN3874) plus a power law. We found an accepetable model
(chi2_red=1.01) with a NH_loc=(1.7+/-1.3)x10^21 cm-2 and a power
law photon index of 2.0+/-0.2 (90% confidence level).