A NASA project to measure gamma rays from extrasolar sources
Background
High energy gamma ray astronomy has recently made a number of
extremely exciting discoveries that will drastically change our
view of large, dynamic astrophysical systems. Due to the
blanketing effect of our atmosphere, almost all of observations
of these systems are being made by satellite detectors with
limited apertures or ground-based detectors that can only see
sources at very high energies. Given the tremendous expense and
long lead times for producing satellite observatories,
recent interest
has turned to flying balloon-borne observatories. Balloons offer
the advantage of being able to get to near-space conditions (above
99% of the earth's atmosphere) cheaply, reliably, and most importantly,
they can be easily recalled if an experiment isn't working.
Dramatic space repairs are not needed and technology for the
observatory can be rapidly updated.
This project aims to produce one of the first large-diameter
(radius of about 1 meter) balloon-borne
telescopes for making
optical images. A rough drawing of the balloon platform
layout is shown here.
These images will be used primarily for locating
the orientation of the telescope array. Included with the telescope
is an air Cerenkov detector which will detect the presence of
gamma rays through their conversion to electron-positron pairs
in the upper atmosphere. The electron-positron pairs subsequently
produce the
Cerenkov radiation observed
by the telescope and
Phototube detector. Optical images
of stars are measured via the
CCD array. Directional pointing information
will be obtained from both optical targets and the
GPS system.
The major components include the telescope with its CCD array,
the GPS antennae and receivers, the computer data acquisition
array, and the
electronics package along with
its associated
cooling.
larryg@upenn5.hep.upenn.edu
