TABLE OF CONTENTS:
INTRODUCTION AND BACKGROUND:
This was the first notice type that was distributed,
by the then called BACODINE system.
It is called the BATSE-Original Notice (or sometimes in the old literature
the "BACODINE GRB Coords Notice").
It reports a GRB location based on the first
1 or 2 seconds of the burst light curve after the BATSE trigger.
Obviously,
integrating the burst light curve for longer intervals would be useful,
but minimizing the time delay between the start of the burst
and the delivery to the sites is paramount.
THE SEQUENCE OF ACTIVITIES:
The BATSE-Original Notice uses the first 1 or 2 1.024-sec rate samples
after the BATSE trigger to calculate the burst location.
The exact sequence of steps is:
a) The program continously scans the incoming telemetry stream from
the CGRO spacecraft looking for the trigger-flag to be set.
During this, it is also calculating the background rates averaged over a 10-sec
sliding window in all 8 LADs in all 4 DISCLA energy intervals
(20-50-100-300-infinity keV).
b) When the trigger flag is set, the program checks to see in which
of the two 1.024-sec samples the rate increase occurs. There is
a 5.0-sigma increase above background requirement so that the GCN
program has enough signal with which to calculate a useful location.
It uses the previously accumulated
background count rates to find the source-only rates.
If there is no 5-sigma increase, then the program continues searching
the incoming telemetry stream until there is or for up to 10 seconds
(whichever comes first). This searching-for-enough allows for bursts
which have slow risetimes.
c) The program then finds the 3 brightest detectors in the middle two
energy bins (50-300 keV).
d) The source-only count rates in these 3 detectors are the solutions
to the dot-product of the 3 normal vectors for the detectors and the
burst direction vector.
e) These 3 simultaneous equations are solved for the burst direction vector.
This solution assumes an "ideal physics response function" for the detectors.
This is not strictly true (there are non-cos(theta) and scattering
distortions to the ideal response), but remember we are going for minimum
time delay with these Original Notices.
f) This direction which is in spacecraft-centered azimuth-elevation coordinates
is converted to the RA,Dec coordinate system using the spacecraft
orientation information from the engineering portion of the telemetry
stream.
g) These RA,Dec coordinates plus an uncertainty and an intensity are combined
with some other ancillary information and distributed to those sites
requesting this notice type via all the distribution methods.
Depending on the relative phasing of the burst with the two 1-sec rate sample accumulations within each telemetry frame, the Original Notice can be available for distribution as short as 3.5 sec or as long as 5.5 sec after the start of the burst. If it is a slow risetime GRB, then it can be delayed by up to 15.7 sec.
And for every Original Notice issued, there will be a Final Notice (even if it was a short burst and no new rate samples were added to the integration of the light curve). If the trigger is determined to be a true GRB and it is bright enought to meet the LOCBURST criteria, then a LOCBURST Notice is issued. There may or may not be a MAXBC Notice issued depending on the presence of telemetry from the spacecraft at the T+10min time after the trigger.
IMPORTANCE OF THIS ORIGINAL NOTICE:
While it does not have the smallest location error, the importance
of this Notice type is that it has the shortest of all the time delays
(T + 3.5-5.5sec).
Sites with fully automated computer-controlled fast-slewing telescopes can
receive the notice, slew to the location, and be on target while many of the
GRBs are still bursting.
LOCATION ERROR:
The brighter the initial part of the burst the smaller the location error.
Bright bursts have typical errors of 5 degrees radius and the
burst right at threshold have errors of 10-15 degrees radius.
More information is available here.
These errors will improve when Geoff Pendleton and I complete the addition
of the BATSE-team's "locburst" algorithm into the program.
DISTRIBUTION METHODS & FILTER FUNCTIONS:
As with all the GCN notice types, these BATSE-Original Notices
are available to the GCN community via the Internet socket, e-mail,
alpha-numeric pager (long & short versions), phone/modem, and cell-phone
distribution methods.
The available filter functions are: ALL, VISIBLE, NIGHT, and various
custom filters. See for more details on the filter capabilities.
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 packets. Those GCN sites using the
Internet socket method should refer to the
socket definition document
to get the details (this is packet_type=1).
RECOGNITION:
Sites are encouraged to include Scott D. Barthelmy and Paul Butterworth
in the author list of IAU Circulars, journal papers and conference
presentations
based on observations using these GCN/BATSE-Original locations.
FURTHER HELP:
For more information, please contact me:
Phone: 301-286-3106
E-mail: scott@lheamail.gsfc.nasa.gov
TITLE: BACODINE BURST POSITION NOTICE
NOTICE_DATE: Sat 11 Oct 97 11:50:57 UT
NOTICE_TYPE: Original
TRIGGER_NUM: 6425
GRB_RA: 210.10d {+14h 00m 23s} (J2000),
210.06d {+14h 00m 14s} (current),
209.25d {+13h 57m 01s} (1950)
GRB_DEC: -55.98d {-55d 58' 50"} (J2000),
-55.97d {-55d 58' 11"} (current),
-55.74d {-55d 44' 19"} (1950)
GRB_ERROR: 3.5 [deg radius, statistical only]
GRB_INTEN: 2856 [cnts] Peak=2856 [cnts/sec]
GRB_TIME: 42652.32 SOD {11:50:52.32} UT
GRB_DATE: 10732 TJD; 284 DOY; 97/10/11
GRB_SC_AZ: 333.32 [deg] {XScan=-6.18}
GRB_SC_EL: 76.12 [deg] {Zenith_angle=13.88} {Scan=12.45}
SC_X_RA: 185.94 [deg] (J2000)
SC_X_DEC: 18.91 [deg]
SC_Z_RA: 207.32 [deg]
SC_Z_DEC: -69.80 [deg]
SUN_POSTN: 196.79d {+13h 07m 10s} -7.14d {-07d 08' 16"}
SUN_DIST: 49.95 [deg]
MOON_POSTN: 315.35d {+21h 01m 23s} -13.89d {-13d 53' 25"}
MOON_DIST: 86.81 [deg]
PROG_VERSION: 5.16
PROG_LEVEL: 1
COMMENTS: Definite GRB.
COMMENTS: This notice is based on 1 1.024-sec samples of the light curve.
COMMENTS: In COMPTEL FOV. Possible COMPTEL location to follow.
BACODINE ORIGINAL GRB RA=210.06d DEC=-55.97d TIME: 11:50:52.32 UT I=2856 Definite GRB. COMPTEL FOV.
ORIGINAL RA=209.25 DEC=-55.74d
ORIGINAL RA=210.06 DEC=-55.97d