[vsnet-grb-info 8363] GRB090904A: Correction to enhanced XRT position

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9886
SUBJECT: GRB090904A: Correction to enhanced XRT position
DATE:    09/09/04 12:32:00 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

The automatic enhanced XRT position (GCN 9885) was incorrect and should 
be disregarded. The position was obtained by averaging all the PC data 
from the first orbit, however the degree of pile up in this period 
changes by much more than is normal (see the  light curve at: 
http://www.swift.ac.uk/xrt_curves/00361830/). As a result, the PSF of 
the image did not match any of our calibrated PSFs. We apologise for any 
confusion.

The best XRT position available is the enhanced SPER position, which was 
distributed as an XRT Position Update GCN notice about at 01:27 UT. This 
position is RA, Dec = 100.8858, 50.2038, which corresponds to

RA(J2000.0) =  06h 43m 32.59s
Dec (J2000.0) = +50d 12' 13.6"

with an uncertainty of 2.3 arcsec (radius, 90% confidence).

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