TITLE:   GCN CIRCULAR
NUMBER:  6400
SUBJECT: GRB070509: Swift-XRT Refined Analysis
DATE:    07/05/09 22:09:02 GMT
FROM:    Loredana Vetere at PSU  <vetere@astro.psu.edu>

L. Vetere, J. L. Racusin, D. Grupe, C. Pagani (PSU) and M. Perri (ASDC) report
on behalf of the Swift Team:

We have analysed the first 6.2ks of Swift XRT data from GRB
070509 (trigger number 278903, GCN 6394).
The first orbit  Photon Counting mode image (1.5ks) provides a
refined XRT position at
RA,DEC(J200) = 237.9588, -78.6508 which is

RA(J2000)  = 15h 51m 50.1s
Dec(J2000) = -78d 39' 03.1"

with an uncertainty of 4.1 arcsec (radius, 90% containment).
This is  0.9 arcsec from the initial X-ray position (GCN 6394)
and 1.0 arcmin from BAT refined position (Cummings et al. GCN 6397).

The XRT light curve can be modeled with a broken power law with the
following parameters:
alpha1= -0.3 +/- 0.2
tbreak=  341 +/- 120
alpha2= -1.1 +/- 0.2

The X-ray spectrum of the first orbit PC data can be fitted with an
absorbed power law (photon index = 0.8+/-0.2) with an absorbed column
density fixed to the Galactic value (0.91e21 cm^-2; Dickey & Lockman,
1990). The absorbed (unabsorbed) 0.3-10.0keV flux for this spectrum
was 8.8E-12 (9.1E-12) ergs cm^-2 s^-1.

Assuming the source continues to decay at the same rate, we predict
an XRT count rate of 3.5E-4 counts/s at T+24 hours, which corresponds
to an observed (unabsorbed) flux of 5.1E-14 (5.3E-14) ergs cm^-2 s^-1.

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