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FREGATE

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Scientific Instruments

• The gamma-ray instrument, FREGATE, is sensitive to photons in the 6-400 keV energy range. It will provide accurate burst triggers and moderate resolution spectra.

  FREGATE was built by the CESR in Toulouse, France.

• The wide-field X-ray Monitor (WXM) is sensitive in the 2-25 keV energy range, with good energy resolution and localization accuracy to ~10 arc-minutes or better.

  The WXM detectors were built by RIKEN.

• The soft X-ray camera (SXC) is sensitive in the 0.5-10 keV energy range, with very good energy resolution and localization accuracy to 30 arc-seconds or better.

  The SXC was built by the Center for Space Research at MIT

Each HETE-2 instrument operates independently of the others; however, if a burst is detected by one of the instruments, the others are notified and begin collecting data at higher temporal and energy resolution. All instruments utilize on board sensors to determine safe and appropriate operational conditions.

This is a picture of the front end of HETE: refer to the clickable image below for details!

This is a clickable map: click on the features you would like to understand better.

HETE Instrument Sensitivity

The sensitivity of the HETE scientific instruments can be compared to the BATSE limiting sensitivity by assuming a photon spectral index for the burst and extrapolating the flux in the BATSE 50-300 keV range to the energy ranges of the three HETE instruments. The results for a one-second and a ten-second burst are shown in these tables.

For a typical GRB (spectral index ~ 1.5), HETE is comparably sensitive to BATSE for 1 second duration bursts in the HETE's mid-X-ray band, and more sensitive than BATSE for 10 second duration bursts in all 3 HETE-2 spectral bands. For flat spectra bursts (spectral index ~ 1), HETE is less sensitive than BATSE in all 3 bands for both 1 sec and 10 sec duration bursts. For steep spectra bursts (spectral index ~ 2), HETE is more sensitive than BATSE in all 3 bands for both 1 sec and 10 sec duration bursts.

For comparison, we show two figures from Strohmeyer et al that give the distribution in GRB spectral indices measured by Ginga and BATSE. These spectra are typical of those expected to be observed by HETE-2.