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Gamma Ray Burst

The Ulysses solar X-ray/cosmic gamma-ray burst instrument comprises both soft and hard X-ray detectors. The design of the GRB experiment had to took into account several constraints. A radiation-hardened microprocessor was required to survive the passage through the Jovian radiation belts and the ones available during the design phase of the GRB experiment dictated simplified operating modes for the experiment. Another important constraint was the environment conditions imposed by the spacecraft's powering system: the Radioisotope Thermoelectric Generator (RTG). To minimize the interference from the RTG, the sensors had to be mounted on the magnetometer boom, and were required to be essentially amagnetic (the remnant field could not exceed 2 × 10-5 G at 25 cm).

Hard X-ray detectors
The hard X-ray detector was designed to operate in the nominal energy range 15-150 keV. The sensor shape was chosen to have a nearly isotropic response, because being located on the magnetometer boom allows for a nearly all-sky visibility. The system consists of two 3-mm thick by 51-mm diameter CsI(Tl) crystals mounted via a plastic light guide to two photomultiplier tubes.

Soft X-ray detectors
The soft X-ray sensors were designed as solar X-ray monitors for the energy range ≈ 5-20 keV. They consist of two 500-µm thick, 0.5-cm²-area Si surface barrier detectors. A 100 mg cm-2 beryllium foil front window rejects low energy X-rays and defines a conical field of view of 75° half-angle. The amplified pulses of the two Si detectors are analyzed by a hybrid stack of six-level discriminators which define four differential energy channels and two integral channels.

Summary of Objectives

The three main scientific objectives of the GRB experiment are:

  • The study and monitoring of solar flare X-ray emission
  • The detection and localization of cosmic gamma-ray bursts
  • The in-situ detection of Jovian auroral X-ray radiation

Last Update: 08 December 2006

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