TITLE:   GCN CIRCULAR
NUMBER:  4565
SUBJECT: GRB 060121: Swift XRT refined analysis
DATE:    06/01/22 18:46:38 GMT
FROM:    Pat Romano at OAB-Swift  <romano@merate.mi.astro.it>

V. Mangano, V. La Parola, T. Mineo (INAF-IASFPA), P. O'Brien (UL),
P. Romano (INAF-OAB), D.N. Burrows (PSU), M. Chester (PSU),
L. Angelini (GSFC) on behalf of the Swift XRT team:

The Swift XRT instrument began observing the HETE-discovered GRB 050121
(Arimoto et al., GCN 4550; Prigozhin et al., GCN 4551) at 01:21:37 UT
on 22 January 2006 (Mangano et al., GCN 4560) 10.6 ks after the burst.

Further analysis of the first 5 ks of XRT data of GRB 060121
spanning three orbits (Mangano et al., GCN 4560)
revealed that the source is fading with a power law decay index
of -1.08 + / - 0.24.

The average spectrum is well fitted by an absorbed power law
model with a photon index of 2.07 + / - 0.25 (90% confidence level).
The best fit absorption column of (7.8 + / - 4.5)e20 cm^-2 is
slightly in excess of the Galactic absorption column of 1.7e20 cm^-2.
The average unabsorbed 0.2-10 keV flux in the time range
10.6 - 22 ks after the trigger is at the level of
4.6e-12 ergs cm^-2 s^-1.
The predicted flux at 24 hours after the trigger is at the
level of 6.8e-13 ergs cm^-2 s^-1 (corresponding to a count rate
of about 1.1e-2 counts/s).
New observations are being performed. 

According to NED, the nearest two galaxies with known redshifts
are SDSS J091016.39+453819.9 and SDSS J091023.53+454159.8 with a
redshift of 0.154357 and 0.154272, respectively.
They are 4.5 and 6 arcmin from the Swift GRB position
(Mangano et al., GCN 4560).