TABLE OF CONTENTS:
INTRODUCTION
The GCN system has been modified to incorporate the distribution
of BATSE GRB locations using the MSFC Huntsville LOCBURST processing. This will
produce GRB locations in near real-time with much smaller errors than the
GCN/BATSE-Original, -Final and -MAXBC Notice locations.
SEQUENCE OF ACTIVITIES
The data flow and processing procedure are:
a) GCN detects a GRB trigger and beeps the "Huntsville person on call", (1-3 min)
b) It then automatically ftp's the raw telemetry data to MSFC, (5 min)
c) Where the person looks at the data and produces a location using their
standard LOCBURST algorithm. (10-15 min)
The delay time from the start of the burst to the sending of the notices is 15-35 minutes! This includes the 5 minutes of post-trigger data collection and auto-ftp-ing to Huntsville, and 10-30 minutes of processing in Huntsville.
The advantages of the Huntsville algorithm are that:
a) More data are used. They use the entire GRB light curve, whereas
GCN uses only the first 1-2 seconds of the light curve for
the Original Notices or up to 32 seconds for the Final Notices.
However, only DISCLA data are used; the CONT spectral data is not used
at this time.
b) There are "humans in the loop" which allow for better data selection.
This includes making pre- and post-trigger background selections.
GCN uses only pre-trigger data for the background subtraction
and it uses a small and fixed amount -- the program can not be as smart as
a human in selecting high quality, artifact-free data for the background.
c) The non-cos(theta) detector angular response and atmospheric scattering
corrections are applied. This is the most important improvement.
CRITERIA
LOCBURST locations will only be computed for the brighter bursts -- those
having a peak intensity greater than 2000 +/-20% (the +/- is due to subtleties
in the processing). This will yield a LOCBURST notice of order once a week.
ERROR BOXES
Using this intensity cut, the errors in this rapid form of the LOCBURST
processing will be less than 2deg statistical (68% C.L.)
with a 2deg systematic (68% C.L.) contribution.
The brighter the burst the smaller the statistical contribution.
These two contributions should be added in quadrature.
A distribution of statistical errors is shown in
this figure and a table of total errors in
this table.
DISTRIBUTION METHODS & FILTER FUNCTIONS
These new data sources will be distributed using the same methods/media
(Internet sockets, e-mail, long & short pagers, and dialed phones), the same
formats (see an example of the e-mail attached below), the same filters
(all, visible, night, intensity, and custom),
as with the current GCN (BACODINE) notices.
And if sites find they want different filtering for the different data types,
they can have two entries in the "sites.cfg" file.
Sites can also elect to receive only the LOCBURST location
(they need not receive the BATSE-derived locations).
FORMATS:
An example of the e-mail format is shown below.
It is based on a "TOKEN: value" scheme to allow for
both the easy reading by humans and the easy parsing by computer daemons.
The details of the format and content of the-mail form are described in
E-mail Definition Document.
Examples of the pager, short_pager & subject-only forms are also
attached below.
The packing format and content of the socket packet method is also very
similar to that used in the Original/Final/MAXBC packets.
Those GCN sites using the Internet socket method should refer to the
socket definition document
to get the details (this is packet_type=24).
RECOGNITION
Sites using these locations should reference in publications the
particular burst(s) used through their GCN notice(s). To recognize
the significant effort put into providing rapid GRB locations, sites
are also encouraged to include R. Marc Kippen, Valerie Connaughton,
Geoff Pendleton, and the duty scientist at the time of the burst
(either one of the above; or P. Woods, T. Giblin or M. McCollough) for
BATSE-LOCBURST; and Scott D. Barthelmy & Paul Butterworth for GCN as
co-authors in publications discussing follow-up observations using
these locations. We invite collaborations with any interested observers.
FURTHER HELP
For further information on this, please contact
Marc Kippen (for MSFC issues;
phone: 205-544-7357), or
Scott Barthelmy (for GCN issues;
phone: 301-286-3106),
or see the MSFC-BATSE,
BATSE RBR,
and these
GCN
web pages.
An example of the E-mail form of distribution is shown below. The details of the format and content of this form are described in E-mail Definition Document.
TITLE: BACODINE/HUNTSVILLE/LOCBURST BURST POSITION NOTICE
NOTICE_DATE: Tue 29 Apr 97 12:50:17 UT
NOTICE_TYPE: Locburst
TRIGGER_NUM: 6214
GRB_RA: 34.44d {+02h 17m 45s} (J2000),
34.40d {+02h 17m 36s} (current),
33.72d {+02h 14m 53s} (1950)
GRB_DEC: +26.63d {+26d 37' 56"} (J2000),
+26.62d {+26d 37' 12"} (current),
+26.40d {+26d 24' 06"} (1950)
GRB_ERROR: 0.7 [deg radius, statistical only]
GRB_INTEN: 8213 [cnts] Peak=8213 [cnts/sec]
GRB_TIME: 41784.33 SOD {11:36:24.33} UT
GRB_DATE: 10567 TJD; 119 DOY; 97/04/29
GRB_SC_AZ: 353.15 [deg] {XScan=-5.92}
GRB_SC_EL: -30.07 [deg] {Zenith_angle=120.07} {Scan=120.25}
SC_X_RA: 47.92 [deg] (J2000)
SC_X_DEC: -1.05 [deg]
SC_Z_RA: 138.15 [deg]
SC_Z_DEC: -53.46 [deg]
SUN_POSTN: 36.80d {+02h 27m 12s} +14.56d {+14d 33' 30"}
SUN_DIST: 12.27 [deg]
MOON_POSTN: 302.17d {+20h 08m 40s} -15.72d {-15d 43' 00"}
MOON_DIST: 98.91 [deg]
PROG_VERSION: 1.19
PROG_LEVEL: 3
COMMENTS: Locburst Coordinates.
COMMENTS: Definite GRB.
An example of the (regular) pager format is shown below. There are no "Subject" lines for these e-mails sent to the pager companies because the Subject line would use up valuable character counts from the maximum displayable for the body of the message. The RA,Dec are Current Epoch.
GCN/LOCBURST GRB RA=34.40d DEC=+26.62d TIME: 03:25:45.00 UT I=3421 Definite GRB. Locburst Coordinates.
An example of the short-form pager format is shown below. There are no "Subject" lines for these e-mails sent to the pager companies because the Subject line would use up valuable character counts from the maximum displayable for the body of the message. And it was the very limited display character count of some companies that motivated the short-form pager method in the first place. The RA,Dec are 1950 Epoch.
LOCBURST GRB RA=33.72 DEC=+26.40d
An example of the Subject-only pager/cell_phone format is shown below. Only the "Subject" line for these e-mails sent to the pager companies because that's the only part of the e-mail they display on the pager/cellphone. The RA,Dec are Current Epoch.
LOCBURST RA=34.40 DEC=+26.62d