TO: All GCN Notice recipients RE: Fermi-LAT_Update_Position Notice type is available DT: 28 Feb 09 INTRODUCTION: The GCN system has been modified to incorporate the distribution of positions of GRBs detected by the LAT instrument on the Fermi spacecraft. These LAT-based Notices are the results of on-board (realtime) processing. They are called the LAT_Update Notice type. (There are 2 other LAT-based Notice types, but they are not ready for public distribution - they may be announced later.) About 5 times per year, the flight software in LAT will detect a burst. The time delays for the LAT_Update are in the 10-20 sec range. The location uncertainties are in the 10-100 arcmin range. ACTION ITEM: If, after reviewing the information below, you want to receive these Fermi-LAT_Update Position notices, please send me a request to have them enabled. You can do this by forwarding this email to scott@milkyway.gsfc.nasa.gov . (You can also request changes to any part of your configuration. A reminder: Fermi-GBM notice types were added back in Oct 2008, the SIMBAD_NED search_results notice type in Aug 2008, and AGILE notice types in July 2008.) NOTICE TYPES, CONTENT, and PURPOSE: There are 3 LAT Notice types. (Currently, only the "Update" type is being made available by the Fermi-LAT Team for public distribution.) They are: 1) LAT_Initial Position Notice contains the position using the initial (smallest) portion of the data. They are issued 1 time per trigger. This type is not yet available for public distribution. 2) LAT_Update Notice contains the RA,Dec location for the burst detected by LAT. They are calculated by the on-board Flight software. They are issued 6 times per burst. Currently ONLY the 2nd of these Updates is available for public distribution. The rationale for this choice of public distribution or not is a trade between the amount of source photons collected and background photons collected. The LAT Team decided that this "2nd Update" notice contains, on average, the best balance of signal and noise. 3) LAT_Ground_Refined_Position Notice contains the RA,Dec location for the burst detected by LAT. The positions are calculated by automated ground software 4-6 hours after the burst trigger. More sophisticated algorithms are applied to the data to improve the location accuracy. There can be 0, 1, or more instances of this Notice Type per trigger. This type is not yet available for public distribution. 4) Test Notice is identical in format and content to the 3 Position Notices except that the Test Notices contain computer-generated RA,Dec locations and all the other fields. These Test Notices are generated by the GCN computer every ~3.6 hrs. They allow the receiving site to practice on the Position Notice types. This LAT_Test type has been available for many months. ERRORS and TIME_DELAYS: The timescales and localization precisions of the various notice types are as follows: TIME SINCE LOCATION TYPE BURST ACCURACY COMMENTS ========= ============ ========== ======== Initial 2-4 sec 10-100 arcmin On-board processing (Not public) Update 2-32 sec 10-100 arcmin On-board processing (2nd of 6 is public) Gnd_Refined 4-6 hrs 5-30 arcmin Ground processing (Not yet public) GRB CONFIDENCE LEVEL: The LAT Team has also required that only those LAT_Update_Position notices that have a summed Temporal_statistic plus Image_statistic greater than 120 will be distributed to the public. This threshold filtering removes a large number of "noise" triggers. It is expected that the percentage of these ">120"-Update Notices will be >99.9% real GRBs. ARCHIVE STORAGE: The GCN/FERMI Notices are archived within the GCN website in the Table of FERMI GRBs: http://gcn.gsfc.nasa.gov/gcn/fermi_grbs.html This archives both the GBM Notice types and the LAT_Update notice type. MORE INFORMATION: Can be found at: http://gcn.gsfc.nasa.gov/gcn/fermi.html NOTICE EXAMPLE: Here is an example of a full-format email LAT_Update Position Notice: TITLE: GCN/FERMI NOTICE NOTICE_DATE: Tue 17 Feb 09 04:57:02 UT NOTICE_TYPE: Fermi-LAT Update Position RECORD_NUM: 2 TRIGGER_NUM: 256539404 GRB_RA: 214.417d {+14h 17m 40s} (J2000), 214.536d {+14h 18m 09s} (current), 213.764d {+14h 15m 03s} (1950) GRB_DEC: -4.383d {-04d 22' 59"} (J2000), -4.425d {-04d 25' 30"} (current), -4.153d {-04d 09' 09"} (1950) GRB_ERROR: 57.00 [arcmin radius, statistical only] GRB_INTEN_TOT: 18 [cnts] GRB_INTEN1: 7 [cnts] (0-100 MeV) GRB_INTEN2: 6 [cnts] (0.1-1 GeV) GRB_INTEN3: 3 [cnts] ( 1-10 GeV) GRB_INTEN4: 2 [cnts] (10-up GeV) INTEG_DUR: 3.169 [sec] TRIGGER_INDEX: 0 GRB_DATE: 14879 TJD; 48 DOY; 09/02/17 GRB_TIME: 17805.09 SOD {04:56:45.09} UT SOLN_STATUS: 0x30000003 TEMP_TEST_STAT: 81.50 (log(prob), time domain) IMAGE_TEST_STAT: 53.25 (log(prob), image domain) SUN_POSTN: 330.81d {+22h 03m 14s} -11.94d {-11d 56' 20"} SUN_DIST: 114.57 [deg] Sun_angle= 7.8 [hr] (West of Sun) MOON_POSTN: 238.87d {+15h 55m 29s} -25.36d {-25d 21' 40"} MOON_DIST: 31.36 [deg] MOON_ILLUM: 47 [%] GAL_COORDS: 339.67, 52.23 [deg] galactic lon,lat of the burst (or transient) ECL_COORDS: 213.65, 8.86 [deg] ecliptic lon,lat of the burst (or transient) COMMENTS: Fermi-LAT Coordinates. COMMENTS: The BurstID came from GBM. The socket packets contents 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