TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5393 SUBJECT: GRB 060728: Upper limits of the X-ray emission DATE: 06/08/03 20:52:00 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani (PSU), D. Morris (PSU) and D.N. Burrows (PSU) report on behalf of the Swift-XRT team: The XRT performed 2 observations of the field of GRB 060728 (GCN 5360), starting at 2006-07-28-22:26:35 UT (124 seconds after the BAT trigger) to 2006-07-29-19:06:56 UT and from 2006-08-02-01:41:22 to 2006-08-02-22:57:56 UT, collecting 17.8 and 13.2ks of data in PC mode respectively. No new source is detected within the BAT refined error circle (GCN 5363) in either of the two exposures. The 3 sigma upper limit on the count-rate is 1.0e-3 counts/sec for the first observation, which corresponds to an unabsorbed flux of 4.0e-14 erg cm-2 s-1 in the energy range 0.3-10 keV, assuming a Crab-like spectrum, and 1.2e-3 counts/sec for the second observation (unabsorbed flux of 4.8e-14 erg cm-2 s-1). Combining the two observations the 3 sigma upper limit is 9.2e-4 counts/sec, corresponding to an unabsorbed flux of 3.7e-14 erg cm-2 s-1. This is the first case of a long GRB for which Swift performed a prompt slew without a decection of the afterglow by the XRT. The only previously undetected X-ray afterglow of a long GRB discovered by Swift is GRB 050911 (Page et al. 2006), for which the XRT observations started 4.6 hours after the BAT trigger.