TITLE: GCN CIRCULAR NUMBER: 9331 SUBJECT: GRB 090510: Swift detection of a short hard burst DATE: 09/05/10 00:41:41 GMT FROM: Scott Barthelmy at NASA/GSFC E. A. Hoversten (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), M. M. Chester (PSU), D. Grupe (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (MSSL), D. M. Palmer (LANL) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 00:23:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090510 (trigger=351588). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 333.555, -26.606 which is RA(J2000) = 22h 14m 13s Dec(J2000) = -26d 36' 19" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single spike with a duration of about 0.5 sec. The peak count rate was ~21000 counts/sec (15-350 keV), at 0 sec after the trigger. The XRT began observing the field at 00:24:34.6 UT, 94.1 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 333.55195, -26.58345 which is equivalent to: RA(J2000) = 22h 14m 12.47s Dec(J2000) = -26d 35' 00.4" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 81 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.66e+20 cm^-2 (Kalberla et al. 2005). UVOT took a finding chart exposure of 150 seconds with the White filter starting 97 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image does not include the position of the XRT candidate. The 8'x8' region for the list of sources generated on-board covers the XRT position and 100% of the BAT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02. We note the existence of the galaxy 2dFGRS TGS176Z296 at a distance of 140 arcsec from the XRT position. Burst Advocate for this burst is E. A. Hoversten (hoversten AT astro.psu.edu). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)