TO: All GCN Notice recipients RE: Fermi-GBM Notice types are available (again) DT: 17 Oct 08 INTRODUCTION The GCN system has been modified to incorporate the distribution of positions of GRBs detected by the GBM instrument on the Fermi spacecraft. Currently, there are only Notices of GBM detections; the LAT instrument has not fully developed their detection processing yet. About 200 times per year, there will be a GRB in the FOV (field of view) of the GBM instrument that is bright enough to be localized. Fermi transmits these localizations through the TDRSS system to the ground within 10 sec after the trigger. There is further automated processing of these messages and then they are sent to GCN. If that burst position meets the your site's filtering criteria, then it gets the Notice. Prior to this, the GBM team has been using only the Circulars to distribute their burst detections. Now with the Notices, it will be easier for the automated telescopes to make folow-up observations. Like all the other sources of GRB information within the GCN system, users can elect to receive (or not) each of these Fermi-GBM Notice types. ACTION ITEM: If, after reviewing the information below, you want to receive these Fermi-GBM Position notice types, please send me a request to have them enabled. You can do this by forwarding this email to scott@milkyway.gsfc.nasa.gov Or you can visit the GCN Site Configuration page: http://gcn.gsfc.nasa.gov/gcn/config_builder.html to specify a modification to your site's configuration. (Since I will be at the Huntsville GRB Meeting next week, it may take me a little longer than usual to update your site's configuration.) NOTICE TYPES, CONTENT, and PURPOSE There are 4 GBM Notice types. They are: 1) ALERT Notice is basically just a heads-up timestamp that something further will be coming from Fermi-GBM. It does not contain any RA,Dec location -- only the timestamp and trigger number. They are issued 1 times per burst. 2) GBM_Flight_Position Notice contains the RA,Dec location for the burst detected by GBM. They are calculated by the on-board Flight software. They are issued 1 to 5 times per burst. The Position Notice comes second in the sequence of Notices on the triggers/bursts. Since the position is based on the least-possible amount of data in the processing (just a small initial portion of the burst's lightcurve), it has the lowest significance in the localization process. Even so, the uncertainty in the position is ~15 deg for the at-threshold bursts and ~5 deg for the bright bursts. (Both the 'at-threshold' and 'bright' refer to only the amount of photons in the time interval of the trigger-sampling interval of the burst lightcurve, not to the total burst duration.) It should be noted that even though this Notice type is called the GBM_GND_POSITION, it contains detections of both GRBs and hard x-ray transients. There is both flight- and ground-software in place to correctly identify bursts from transients, but this identification is not 100% perfect. 3) GBM_Ground_Position Notice contains the RA,Dec location for the burst detected by GBM. The positions are calculated by ground software. More sophisticated algorithms can be applied to the data to improve the location accuracy. Also, more data from the on-going progresion of the burst lightcurve is used in this calculation. There can be 0, 1, of more instances of this Notice Type per trigger. 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. POSITION TYPES, ERRORS, and TIME_DELAYS: The automated on-board GBM flight software will generate GRB position notifications in real time. The timescales and localization precisions of the various notice types are as follows: TIME SINCE LOCATION TYPE BURST ACCURACY COMMENTS ========= ============ ========== ======== Alert 2-4 sec n/a On-board procesing Flght_Pos 2-7 sec 5-15(tbr) deg On-board processing Ground_Pos 10-300 sec 3-5(tbr) deg Ground processing SEQUENCE OF ACTIVITIES: The sequence of activities for a typical burst follows: 1) The GBM instrument detects a rate increase (a "trigger"). 2) The Alert message is generated and transmitted via TDRSS. 3) The GBM position is calculated (on board) and the messages is generated and transmitted. 4) If the LAT has a significant enough detection (if it is in the LAT FOV), then a position is calculated, a messages generaged and transmitted. (There is another scenario where LAT makes the initial detection.) 5) There most of the time there will be ground-based ground-calculated improved locations and these will be generated (and distributed) within 10-300 sec. THE Fermi-GBM-to-GCN-to-WORLD PROCEDURE: All 3 types of GBM messages go through or originate in the GBM intrument operations and are then sent to GCN. GCN reformats the messages into the standard GCN_Notice formats, and distributes them to the sites using the usual distribution methods and filtering. The additional time_delay for the GCN processing is never more than 0.3 sec. 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 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 GBM Flight_Position Notice: TITLE: GCN/FERMI NOTICE NOTICE_DATE: Fri 17 Oct 08 11:22:55 UT NOTICE_TYPE: Fermi-GBM Flight Position RECORD_NUM: 49 TRIGGER_NUM: 245935358 GRB_RA: 106.783d {+07h 07m 08s} (J2000), 106.884d {+07h 07m 32s} (current), 106.211d {+07h 04m 51s} (1950) GRB_DEC: -14.450d {-14d 26' 59"} (J2000), -14.464d {-14d 27' 50"} (current), -14.371d {-14d 22' 14"} (1950) GRB_ERROR: 17.33 [deg radius, statistical only] GRB_INTEN: 76 [cnts/sec] DATA_SIGNIF: 5.50 [sigma] INTEG_TIME: 2.048 [sec] GRB_DATE: 14756 TJD; 291 DOY; 08/10/17 GRB_TIME: 40957.44 SOD {11:22:37.44} UT GRB_PHI: 87.00 [deg] GRB_THETA: 80.00 [deg] HARD_RATIO: 1.02 LOC_ALGORITHM: 3 (version number of) MOST_LIKELY: 50% GRB 2nd_MOST_LIKELY: 29% Generic SGR DETECTORS: 0,1,1, 0,0,0, 0,0,0, 0,0,0, 0,0, SUN_POSTN: 202.66d {+13h 30m 37s} -9.48d {-09d 28' 46"} SUN_DIST: 93.15 [deg] Sun_angle= 6.4 [hr] (West of Sun) MOON_POSTN: 57.03d {+03h 48m 08s} +25.00d {+24d 59' 59"} MOON_DIST: 62.59 [deg] MOON_ILLUM: 91 [%] GAL_COORDS: 227.57, -3.14 [deg] galactic lon,lat of the burst (or transient) ECL_COORDS: 110.41,-36.71 [deg] ecliptic lon,lat of the burst (or transient) COMMENTS: Fermi-GBM Flight-calculated Coordinates. 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