The following appeared in the ??? ?? AAS HEAD News Letter
BACODINE: The BATSE Coordinates Distribution Network
by Scott Barthelmy (scott@xtelab.gsfc.nasa.gov), Neil Gehrels, Thomas Cline (NASA/GSFC); Jerry Fishman, Chip Meegan, Chryssa Kouveliotou (NASA/MSFC)
The Gamma Ray Burst (GRB) puzzle remains one of astrophysics' great problems 25 years after their first discovery. Follow-up observations on GRB locations are being made with ever decreasing time delays, but still no source objects for GRBs have been identified. The BATSE instrument on GRO detects roughly one GRB per day. All the data are telemetered to the ground in real time with no on-board storage. The purpose of BACODINE is to process the data as quickly as possible and deliver the coordinates for a GRB to ground-based instruments to make follow-up observations while the burst is still occuring.
BACODINE is completely automated and runs 24 hours a day. It listens to the real-time telemetry data from GRO-BATSE and calculates a set of rough coordinates for a GRB quickly -- the total time between when the first gamma rays from a burst hit the BATSE detectors to when the coordinates are available on the ground is 3.5 to 5.5 seconds. These coordinates are then distributed to many sites around the world so that multi-band, follow-up observations can be made. The goal, of course, is to "see" some well localized emission and identify the counterpart to the GRB.
To handle a wide variety of situations and to maximize the number of sites and instruments making follow-up observations, the BACODINE system distributes the BATSE GRB coordinates via dedicated phone lines, Internet socket connections, e-mail, and paging beepers. While the first is the fastest distribution method, 0.3 sec maximum distribution time, Internet sockets, 0.5 to 2 seconds, and e-mail, 5 to 30 seconds, are still very fast, cheaper and offer the convenience of BACODINE-computer-to-site-computer linkage. For sites that do not have Internet access, the alpha-numeric pagers, 1 to 2 minutes, offer a convenient method of getting the RA,Dec coordinates of the GRBs.
The location determination of the GRB by BACODINE using the BATSE data requires instruments with a wide field of view (FOV) or an ability to tile a large region of the sky in a relatively short time period. The accuracy of the coordinates depends on the burst intensity -- the brighter the burst the smaller the error circle. For example, folding in the sky viewing efficiencies of a ground-based optical instrument, a BACODINE location with an error circle of 12 degrees in radius can be observed once every 3 weeks. For very bright bursts, the observation rate is once every 12 weeks and the error circle is 6 degrees.
In addition to the distribution of BATSE GRB coordinates, the BACODINE system captures the COMPTEL instrument's data when the GRB is determined to be in their FOV and automatically transfers it to their computers. This automation cuts the time to yield a COMPTEL GRB position. BACODINE can also determine if a GRB is in the FOV of other spacecraft, e.g. ALEXIS, and notify appropriate people for a faster response. And in the future, BACODINE will redistribute GRB locations from the MIT HETE spacecraft.
Currently, there are 19 sites around the world receiving BACODINE GRB notices. The optical, radio, and gamma-ray band passes are covered. Three of the sites are fully automated (no humans in the loop) with fast slewing instruments and therefore have the shortest time delay between the onset of the GRB and the first follow-up observation. Both professional and amateurs can make meaningful observations. New collaborations are strongly encouraged by the BACODINE project. Please contact us at the above e-mail address or call 301-286-3106 to discuss becoming part of the BACODINE network.