TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1928
SUBJECT: GRB030226: Analysis of Chandra data
DATE:    03/03/06 07:39:17 GMT
FROM:    Derek Fox at CIT  <derekfox@astro.caltech.edu>

M. Sako and D.W. Fox (Caltech) report on behalf of a larger
collaboration:  

"We find that the detection of excess soft X-ray absorption reported
by Pedersen et al. (GCN 1924) in the Chandra spectrum of GRB030226 is
not required by the data.  A power law of photon index 2.0 +/- 0.1
with Galactic absorption of 1.6 x 10^20 cm^-2 provides a statistically
acceptable fit with chi-squared = 12.6 for 14 degrees of freedom.  The
90%-confidence upper limit on the amount of absorption by neutral
material at a redshift of 1.98 is N_H = 4.8 x 10^21 cm^-2 using the
best current low-energy calibration.  We note that our derived limit
depends sensitively on the calibration below E = 0.4 keV where the
response is known to be strongly time-dependent (see
http://asc.harvard.edu/cal/Acis/Cal_prods/qeDeg/index.html).  The
power-law decay of the flux between 0.3 and 8 keV is found to be
alpha_X = -3.6 +/- 1.0 over the course of the observation (epoch day
1.56 to day 2.02).  This provides a statistically acceptable fit to
the data (chi-squared of 7.3 for the 18 degrees of freedom of a 20-bin
light curve)."