High Energy Telescope
The High Energy Telescope (HET) consists of 19 sub-telescopes, each with a non-overlapping 21°x21° field of view (fully coded). HET and LET capabilities are compared in the table below.
In the schematic at right, one side of a sub-telescope has been removed to see the inside. On the top is the tungsten coded mask, with a 2x7 array of CZT detector modules on the bottom. On each side is a panel of "graded Z" passive shielding made of lead, tin, and copper.
Just above and to the side of the CZT detectors are CsI crystals used for anti-coincidence shielding, part of the HACOS particle and gamma-ray detection system. Scintillation photons from these crystals (2 on each side) are detected by photomultiplier tubes (PMTs). Another set of CsI crystals lies just beneath the CZT detectors to form the rear of the HACOS shielding. HACOS and its gamma-ray detection capabilities are discussed on the Background Shielding page.
| Parameter | HET | LET |
|---|---|---|
| Energy range | 10-300 keV (10-600 keV goal) | 4-30 keV |
| Energy res. (FWHM) | 1-2 keV (10-100 keV) 2-6 keV (100-600 keV) |
0.5 keV |
| Sensitivity (5σ in 1yr) | 0.05 mCrab* (10-100 keV) 0.5 mCrab* (200-600 keV) |
0.05 mCrab* |
| Sens. (5σ each orbit) | 2 mCrab* (10-200 keV) 20 mCrab* (200-600 keV) |
2 mCrab* |
| Field of View (FoV) | 154° x 64°=2.5 sr (fully coded) ~3.6 sr (partially coded) |
160° x 65°=2.5 sr (fully coded) ~3.1 sr (partially coded) |
| Survey coverage | Full sky each orbit (95 minutes) | Full sky each orbit (95 minutes) |
| Pointing accuracy | 0.5° stability, 5" aspect | 0.5° stability, 5" aspect |
| Angular resolution | 6.1' | 1.0' |
| Source localization (5σ) | 74" | 12" |
| Temporal resolution | 10 µs | 10 µs |
| Telescopes | 19 coded-aperture sub-telescopes Each has 21° x 21° FoV |
32 coded-aperture sub-telescopes Each has 16° x 16° FoV |
| Masks | Uniformly Redundant Arrays 5mm thick tungsten 2.5mm square mask pixels |
Uniformly Redundant Arrays 0.5mm thick tungsten 0.2mm square mask pixels |
| Detectors | 5.96 m2 CZT 20mm square crystals, 4mm thick 16x16 1.25mm pixels per crystal |
1.28 m2 Si strip 20mm square crystals 100x100 0.20mm pixels per crystal |
| Collimators/Side Shielding |
20% active (CsI) 80% passive (graded-Z) |
100% passive (graded-Z) |
| Rear shielding | 1.3cm thick CsI | graded-Z |
* 1 mCrab = 10-11 erg/cm2/s in band ΔE=E-0.5E