TITLE: GCN CIRCULAR NUMBER: 7382 SUBJECT: GRB 080310: Swift detection of a burst with optical afterglow DATE: 08/03/10 08:58:27 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. R. Cummings (NASA/UMBC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), S. Campana (INAF-OAB), P. A. Evans (U Leicester), E. A. Hoversten (PSU), S. D. Hunsberger (PSU), C. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 08:37:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080310 (trigger=305288). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 220.081, -0.166 which is RA(J2000) = 14h 40m 19s Dec(J2000) = -00d 09' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a precursor at T-24 seconds and multiple peaks from T-10 to T+6 seconds. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 08:39:27.9 UT, 89.2 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 220.0566, -0.1756 which is equivalent to: RA(J2000) = 14h 40m 13.5s Dec(J2000) = -00d 10' 32.1" with an uncertainty of 5.0 arcseconds (radius, 90% containment). This location is 94 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to assess possible redshift constraints using X-ray spectroscopy and the nH-z relation from Grupe et al. (2007). UVOT took a finding chart exposure of nominal 100 seconds with the White (160-650 nm) filter starting 99 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 14:40:13.80 = 220.0575 DEC(J2000) = -00:10:29.6 = -0.1749 with a 1-sigma error radius of about 0.6 arc sec. This position is 4.1 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.8 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04. Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.nasa.gov). 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.)