TITLE
Rapid Follow-Up Gamma-Ray Burst Locations from BATSE

AUTHORS
\author{R.M. Kippen, G.N. Pendleton}
\affil{UAH, NASA/MSFC}
\author{V. Connaughton}
\affil{NRC, NASA/MSFC}
\author{G.J. Fishman, C.A. Meegan}
\affil{NASA/MSFC}
\author{S.D. Barthelmy}
\affil{USRA, NASA/GSFC}
\author{C. Robinson, C. Kouveliotou}
\affil{USRA, NASA/MSFC}

ABSTRACT
The recent breakthrough discovery of a weak, fading x-ray/optical
source possibly associated with a gamma-ray burst (GRB 970228)
highlights the critical need for rapid and accurate burst locations.
While this need has long been recognized by GRB researchers, its
realization has been difficult to achieve technically.  For the past
four years the BACODINE system has been providing roughly-determined
(accurate to $\sim$4 degrees, at best) BATSE burst locations in
near-real-time (a few seconds) to a network of counterpart searchers.
Unfortunately, BACODINE locations are too inaccurate to allow
sensitive follow-up observations with current instruments.  To
facilitate sensitive and timely counterpart search efforts, we have
developed the BATSE Rapid Burst Response (RBR) system, which provides
locations with improved accuracy ($\sim$2 degrees) for several GRBs
per month within $\sim$10--30 minutes of burst onset.  The BATSE RBR
system uses continuous real-time telemetry data, captured by BACODINE
and transferred to NASA/MSFC, where the burst location algorithm
employed for ``best and final'' BATSE locations is applied.  The
improved burst locations are then distributed to observers through the
existing BACODINE world-wide network.  The BATSE RBR system, combined
with wide-field or scanning instruments, offers a good chance of
detecting fading x-ray/optical counterparts if their lightcurves are
similar to the recently discovered object.  A coordinated follow-up
effort using the RXTE-PCA is in progress which could localize fading
x-ray emission to $\sim$0.1 degrees within a day.  We will discuss the
operation and performance of the new BATSE RBR system with particular
emphasis on measures of burst location accuracy.

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