TITLE:   GCN CIRCULAR
NUMBER:  9977
SUBJECT: GRB 090929A: Swift-XRT non-detection
DATE:    09/09/30 16:21:47 GMT
FROM:    Kim Page at U.of Leicester  <kpa@star.le.ac.uk>

K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team:

Swift performed a short Target of Opportunity observation of GRB 090929A 
about 13 hours after the burst (Rau, GCN Circ. 9962; Cummings & Krimm, GCN 
Circ. 9966; Golenetskii et al., GCN Circ. 9968). This area of sky was a 
hot target for the XRT, so only a short observation was performed, with 
1.4 ks of data being collected in Photon Counting mode.

We do not detect a source within the BAT error circle, to a 90% upper 
limit of 0.015 count s^-1 over 0.3-10 keV. Assuming a typical counts to 
flux conversion of 3.8 x 10^-11 erg cm^-2 ct^-1 (Evans et al., 2009, 
MNRAS, 397, 1177), this corresponds to an observed flux of 5.7 x 10^-13 
erg cm^-2 s^-1. We note that this is not a very constraining upper limit, 
because of the greater than usual background caused by the high XRT CCD 
temperature and the short exposure time.

Filtering out all photons below 1 keV, a more stringent upper limit of 9 x 
10^-3 count s^-1 (1-10 keV; observed flux of ~3.4 x 10^-13 erg cm^-2 s^-1) 
can be determined.

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