TITLE: GCN CIRCULAR NUMBER: 7685 SUBJECT: GRB 080506: Swift detection of a burst with optical afterglow DATE: 08/05/06 18:06:27 GMT FROM: Wayne Baumgartner at GSFC W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), M. M. Chester (PSU), G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), S. Immler (CRESST/GSFC/UMD), J. A. Kennea (PSU), V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester), C. Pagani (PSU), P. Romano (INAF-IASFPA), T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU), T. N. Ukwatta (GSFC/GWU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 17:46:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080506 (trigger=311159). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 329.435, +39.002 which is RA(J2000) = 21h 57m 44s Dec(J2000) = +39d 00' 08" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As this is an image trigger, the BAT light curve does not show meaningful emission from the burst. The XRT began observing the field at 17:48:41.3 UT, 140.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 329.42145, 38.98413 which is equivalent to: RA(J2000) = 21h 57m 41.15s Dec(J2000) = +38d 59' 02.9" with an uncertainty of 3.3 arcseconds (radius, 90% containment). This location is 74 arcseconds from the BAT onboard position, within the BAT error circle. The XRT light curve from TDRSS data is fading. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density, so we cannot provide limits on the redshift using spectroscopy and the relation from Grupe et al. (2007). A summary of the promptly downlinked data is given at http://www.swift.ac.uk/sper/311159/. The initial flux in the 2.5 s image was 5.50e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 400 seconds with the V filter starting 143 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 21:57:41.83 = 329.4243 DEC(J2000) = +38:59:06.4 = 38.9851 with a 1-sigma error radius of about 0.5 arc sec. This position is 8.0 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.3 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected extinction of about 0.8 magnitudes. Burst Advocate for this burst is W. H. Baumgartner (wayne 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.)