TO: All GCN Notice recipients RE: A new burst notice type is available DT: 21 Apr 08 INTRO: There is a new Notice type available within GCN that has GRBs detected by BAT while the Swift spacecraft is slewing (BAT_SLEW_POS). The Harvard group (Antonio Copete and Josh Grindlay) have developed a technique to process BAT event-by-event data captured while Swift is slewing and extract GRB positions during these slew time intervals. DETAILS: Data Analysis Method: Sky images are made from the event data for each 0.2sec interval during a slew. Given the slew rate these 0.2sec intervals result in a slightly less than a 50% increase in the intrinsic angular resolution on the sky. Each 0.2-sec image is added to the total sky image during the slew. Images are built up for the 15-50 (Soft) and 50-150 (Hard) keV bands (plus the sum of the two). These sky images are scanned for point sources above a specified significance threshold, and each source is compared to a catalog. Those sources that do not match the catalog are deemed new sources (ie GRBs). Subclasses: There are two subcategories of the BAT_SLEW_POS detections: a) "Gold plated" which are 100% confidence that they are GRBs (or at least something astrophysical in gamma-rays). b) "Silver plated" detections have somewhat lower thresholds and a somewhat lower confidence level (tbd%). The threshold criteria are: a) Gold: >4 sigma in both the Soft AND Hard bands. b) Silver: >4 sigma in either Soft OR Hard bands AND >4 sigma in Broad band AND at least one of the three bands must be >6 sigma. (The Broad band is the sum of the Soft and Hard bands, ie 15-150 keV) Occurance Rate: Currently, only about 40% of the slews have event data captured. This capture efficiency will likely double within a couple months. But for now (ie the 40% eff), the expected rate of the Gold plated detections is ~6/year and ~50/yr for the Silver plated events. Time Delay: Given that these detections are made using event-by-event data which only comes down the full telemetry Malindi downlinks, there will be a 0.1 to 8 hr delay plus an additional 0.5 hrs for the ground processing. The average delay will be ~3.5 hours. Location Uncertainty: Since these events can be weaker than the normal BAT Rate-trigger or Image-trigger GRBs, the range of position uncertainties will be slightly larger: 1-7 arcmin. The uncertainty is given for each detection. Filtering: Currently, there is no plan for filtering within the GCN based on Silver vs Gold plating. If you have BAT_SLEW_POS enabled, then you will receive both Gold and Silver. While it is not known yet what the GRB-ness confidence level will be for the Silvers, it is epected to be very high, and if experience should prove otherwaise, the threshold level (N_sigmas) will be increased to to achieve a high CL. ACTION ITEM: If you want to receive this BAT_SLEW_POS notice type, please send me a request to have it enabled. You can do this by forwarding this email to scott@milkyway.gsfc.nasa.gov NOTICE EXAMPLE: Here is an example of a full-format email BAT_SLEW_POS Notice: TITLE: GCN/SWIFT NOTICE NOTICE_DATE: Thu 17 Apr 08 17:49:31 UT NOTICE_TYPE: Swift-BAT Slew GRB Position ID_NUM: 4 GRB_RA: 223.800d {+14h 55m 12s} (J2000), 223.870d {+14h 55m 29s} (current), 223.377d {+14h 53m 30s} (1950) GRB_DEC: +48.410d {+48d 24' 36"} (J2000), +48.377d {+48d 22' 36"} (current), +48.612d {+48d 36' 42"} (1950) GRB_ERROR: 6.77 [arcmin radius, statistical only] GRB_INTEN: 785889 [cnts] Image_Peak=0 [image_cnts] TRIGGER_DUR: 70.596 [sec] TRIGGER_INDEX: 8 Criteria: (S(15-50) OR H(50-150)) > 4.0 sigma AND B(15-150) > 4.0 sigma AND (S OR H OR B) > 6.0 ENERGY_RANGE: 15-150 keV BKG_INTEN: 0 [cnts] BKG_TIME: 0.00 SOD {00:00:00.00} UT BKG_DUR: 0 [sec] GRB_DATE: 14573 TJD; 108 DOY; 08/04/17 GRB_TIME: 37993.18 SOD {10:33:13.18} UT SOLN_STATUS: 0x4011 RATE_SIGNIF: 0.00 [sigma] IMAGE_SIGNIF: 4.59 [sigma] SUN_POSTN: 26.08d {+01h 44m 20s} +10.79d {+10d 47' 28"} SUN_DIST: 118.77 [deg] Sun_angle= 10.8 [hr] (West of Sun) MOON_POSTN: 176.72d {+11h 46m 53s} -1.54d {-01d 32' 09"} MOON_DIST: 64.44 [deg] MOON_ILLUM: 93 [%] GAL_COORDS: 82.88, 57.97 [deg] galactic lon,lat of the burst (or transient) ECL_COORDS: 194.51, 60.34 [deg] ecliptic lon,lat of the burst (or transient) COMMENTS: SWIFT-BAT Slew GRB Coordinates. COMMENTS: A point_source was found. COMMENTS: This does not match any source in the ground catalog. COMMENTS: This is not a GRB. COMMENTS: Very high confidence of reality (silver-plated). COMMENTS: This Notice was ground-processed from flight-data. The other email-based formats (long/short/subject pager formates) have the same subset of fields as for the regular BAT_POS Notice type. The socket packet content can be found at: http://gcn.gsfc.nasa.gov/gcn/sock_pkt_def_doc.html Sincerely, Scott Scott Barthelmy NASA-GSFC, Code 661, Greenbelt, MD 20771 PHONE: 301-286-3106 (office) CELL: 301-346-3733 FAX: 301-286-1684 (1st choice, -1682 2nd choice) EMAIL: scott@lheamail.gsfc.nasa.gov PAGER: 3013463733@cingularme.com WEB: http://gcn.gsfc.nasa.gov/gcn