There are two parts to the GRB Coordinates Network (GCN): (1) the distribution of GRB locations detected by various spacecraft, and (2) receiving and automatically distributing to the GRB community prose-style e-mail messages about follow-up observations on various GRBs. There used to be a third part (the original part): the real-time distribution of GRBs detected by CGRO-BATSE (the original BACODINE system),
Part 1 (GCN Notices):
This portion of GCN consists of distributing the GRB
locations determined by the Swift, HETE, INTEGRAL, IPN, RXTE-PCA, RXTE-ASM, BeppoSAX, GRO-COMPTEL,
and ALEXIS (extreme-UV transients)
It is this addition of the other sources (beyond the orignal BATSE source)
of GRB locations that motivated the name change from BACODINE to the more
general GCN name. This combining of all the sources of GCB location
information into a single network means that sites need only maintain a single
interface for all their GRB needs.
The same distribution methods as developed during the BACODINE days are still
available in GCN plus others have been added.
Part 2 (GCN Circulars):
This part allows the GRB community to submit messages to a central queue
where they are automatically distributed (e-mail) to the entire GRB community.
These are prose-style messages
(as opposed to the "TOKEN: value" style of the GCN e-mail notices)
from follow-up observers reporting on their results (detections or nulls) or
for coordinating with others.
Original (but now obselete) Part (BACODINE Notices):
The real-time transmission of the data from the COMPTON-GRO spacecraft allows
for access to BATSE instrument data that can be used to make simultaneous
and near-simultaneous multi-band observations of Gamma Ray Bursts (GRBs).
The GCN system (1) monitors this telemetry stream, (2) extracts the
appropriate information from the BATSE portion, (3) detects the occurrence of a
GRB, (4) calculates the approximate coordinates for the burst, and (5)
distributes those coordinates to instruments, observatories, and other
interested parties around the world. This is done with custom hardware
plus software located at the NASA Goddard Space Flight Center mission operations
center for CGRO. The maximum time delay between the arrival of the GRB
photons at the BATSE detectors and the calculation of the coordinates is 5.5
seconds. The accuracy of the calculated coordinates is ~10 degrees (typical
worst case).
The coordinates can be distributed by phone connections, by direct
computer-to-computer socket connections over the Internet, by e-mail,
and by alpha-numeric pager to any optical, infrared, radio, and TeV telescope
systems with wide field-of-view capabilities.
This rapid distribution of coordinates
(0.3 to 30 sec, depending on the distribution method) allows for a 4 to 6
order of magnitude improvement over
previous efforts in the response time of follow-up observations
of the optical and radio emission of GRBs.
This greatly increases the likelihood of a detection and hence, of
the identification of the quiescent counterparts of GRBs and
solving one of astrophysics' greatest mysteries.
The pictures below show schematically the flow of information through the telemetry system and a world map of the GCN sites. In the left picture the gamma rays from a GRB hit the BATSE detectors on CGRO, and then the telemetry data are transmitted up to a TDRS satellite, down to White Sands, up to DOMSAT, and down to GFSC, where they are processed by GCN. The right picture shows the locations around the world of the various GCN sites.
The GCN contact is: Scott Barthelmy,
scott@lheamail.gsfc.nasa.gov,
(301)-286-3106
This file was last modified on 19-Oct-02.