Fiona A. Harrison and Thomas A. Prince
By eliminating the local neutron star explanation for gamma-ray bursts (GRBs) favored for twenty years, BATSE observations have elevated the origin of GRBs to one of the great outstanding problems in astrophysics. GRB sources are now thought to be distributed either in a large halo (or corona) around the Galaxy or else at cosmological distances. Discriminating between these possibilities and setting the GRB distance scale, now undetermined to five orders of magnitude, is a pivotal observational question unlikely to be solved by continued BATSE observations. Even if BATSE continues observing GRBs for another five years, its statistics will be insufficient to resolve this issue.
Coronal halo models of GRBs predict similar burst halos around other
massive spiral galaxies. Andromeda is an imaging hard
Andromeda is a coded aperture gamma-ray telescope consisting of a hexagonal coded mask coupled to an alkali-halide imaging scintillation detector, a flight-proven technology adapted from the balloon-borne Caltech Gamma-Ray Imaging Payload (GRIP). A 2000 sq cm phoswich detector combines large area with background rejection, making Andromeda more sensitive that any gamma-ray imaging instrument previously flown. Andromeda is currently being considered for launch through the Department of Energy and will be proposed to NASA's Small Explorer program.
============================================================== Energy range 10 - 200 keV Energy resolution 19% FWHM @ 60 keV Collecting area 2320 sq cm Effective area 2000 sq cm @ 30 keV Mask transparency 50% Sensitivity 3.4 x 10e-6 photon/(sq cm)/sec/keV (continuum) (3 sigma in 2 x 10e4 s, (delta E)/E = 50%) Sensitivity 1.6 x 10e-9 erg/(sq cm)/s (transient) (5.5 sigma in 10 s) (10 - 200 keV, photon index = 2) Field of view 10 deg FWHM Angular resolution 1.5 deg Timing capability 100 microsec (relative) ==============================================================
Dr. Fiona Harrison