Gamma and Cosmic Ray Astrophysics

 
 
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Advanced Telescope for 
High Energy Nuclear Astrophysics

ATHENA







The ATHENA mission concept was concieved to undertake a broad observational program in gamma ray astrophysics.  First proposed in the early 1990's, several varients of this baseline design are now in favor, such as the 3-Compton approach.  The basic ATHENA concept was simple: major improvements in performace of a Compton telescope would be realized by improving the detectors that have been used on NASA's COMPTEL instrument. ATHENA would use germanium detectors instead of liquid scintillator and NaI(Tl) scintillators.  The geometry of ATHENA is also modified to increase efficiency. 

ATHENA can significantly extend the scientific investigations initiated with NASA's COMPTON Gamma Ray Observatory with a focus on the high energy nuclear processes occurring in astrophysical sources.   With dramatically improved sensitivity in the 10 keV-30 MeV region, it will provide the first high resolution maps of the Galaxy in several radioactive lines.  ATHENA will also observe several supernovae and novae per year, and provide order of magnitude improved capabilities for the study of compact galactic sources and active galactic nuclei. 

The original baseline instrument (pictured above) combines a high resolution Compton telescope for spectroscopy and imaging in the 0.3-30 MeV energy range, with a coded aperture system for the 10-200 keV observations. The coarse collimator (orange) is designed to limit the low energy field of view for the coded aperture instrument, thus reducing diffuse sky background. The coded aperature and coarse collimator are essentially transparent for gamma rays >300 keV. 

We have modeled the baseline ATHENA configuration in order to demonstrate performance.  The basic results of this work include gamma ray efficiencies, angular resolution, radioactivities induced by the space radiation environment, background rates, and ultimately instrument sensitivity. 

A simple demonstration of sensitivity is provided by a simulation of a hypothetical distribution of 26Al in the Vela supernova remnant as imaged by ATHENA (shown below). 

The field of view in this image is approximately 9 degrees across.  We have distributed the flux of 26Al  (total of  3x10-5g cm-2 s-1 measured by COMPTEL) in a central disk with four knots representing blobs of matter that were ejected from the initial explosion.  Each blob represents  5% of the total flux (1.5x10-6g cm-2 s-1).  The angular scales of our simulation are essentially correct, although there was no attempt to align these blobs with actual features of Vela.  Background events are included in this simulation of a 106 second observation. 

Links to:  Last revised: 7 November 2000