GCN Circular 4529

S. Campana (INAF-OAB), M. Perri (ASDC), P. Romano (INAF-OAB), D.N. Burrows
(PSU), J. Norris (GSFC), K. Hurley (Berkeley) report:

"We have analyzed the first four orbits of XRT data from GRB 060116
(Campana et al., GCN 4519
Not found
 
 
). The GRB afterglow is detected at a mean count
rate of 0.099+/-0.004 count/s during a 5545 s Photon Counting mode
observation. Close to the GRB afterglow (1.2 arcmin) there is a fainter
source (0.017+/-0.002 count/s) coincident with an M4 star. The best fit
position for the GRB afterglow is:
RA(J2000) = 05h 38m 46.22s,
Dec(J2000) = -05d 26m 11.9s
with error radius 3.7 arcsec, less than 1 arcsec from the one reported
in Campana et al. (GCN 4522
Not found
 
 
) based on a shorter observation. This
position is also 1.5 arcsec from the source reported by Kocevski et al.
(GCN 4528
Not found
 
 
).

The X-ray light curve is fading and its decay law is consistent with a
power-law with slope of -0.95+/-0.07 (90% confidence level). No strong
flare activity is observed.

The X-ray spectrum can be fit with an absorbed power law model
with photon index of 2.1+/-0.3 and a column density of (8.1+/-2.5)E21
cm-2, higher than the Galactic hydrogen column density in the direction 
of the burst (NH_gal=2.0E21 cm-2 at b=-19). The mean 0.5-10 keV unabsorbed
flux is 9E-12 erg cm-2 s-1. Fixing the Galactic column density to
the above value we can constrain the GRB redshift to be z<3.2 or z>5.4
(90% c.l., and NH(z)>4E21 cm-2).

If the burst continues to decay at the current rate we estimate an XRT
count rate of 2E-3 counts/s at T+24hr, which corresponds to an observed
0.5-10 keV flux of ~3E-13 ergs cm-2 s-1.