GCN Circular 18391
C. Pagani (U. Leicester), P. A. Evans (U. Leicester) and S. B. Cenko (GSFC) report on behalf of the Swift-XRT Team: The XRT began observing the field of the possible GRB 151004A (Swift trigger 657564, Cenko et al., GCN Circ. 18389) at 19:09:14.0 UT, 3609.3 seconds after the BAT trigger. No source was detected in 1.1 ks of promptly downlinked data, which covered 84% of the BAT error circle. We are waiting for the full dataset to detect and localise any possible XRT counterpart. This circular is an official product of the Swift-XRT team.