INSTRUMENT_HOST_ID = ULY INSTRUMENT_ID = GRB INSTRUMENT_NAME = SOLAR X-RAY/COSMIC GAMMA-RAY BURST INSTRUMENT_TYPE = GAMMA-RAY BURST DETECTOR Instrument Overview =================== The GRB experiment was proposed in 1977 with a twin experiment aboard the NASA spacecraft. This approach had numerous advantages: a carefully intercalibrated pair of experiments at opposite ecliptic latitudes would survey the solar equatorial regions extensively, and stereoscopic observations would be relatively easy to compare with matched detectors. Triangulation baselines for cosmic gamma-ray bursts would be long, and the fact that two detectors in the network would be out of the ecliptic plane would provide a particularly favorable geometry for localization (non-coplanar detectors are required for arrival time analysis). With the unique mission opportunities, however, came unique design constraints. A radiation-hardened microprocessor was required to survive the passage through the Jovian radiation belts; few were available during the design phase of the GRB experiment. The limited performance of the unit chosen dictated simplified operating modes for the experiment. Electrical power aboard Ulysses is provided by a radioisotope thermoelectric generator (RTG) containing 10 kg of 238Pu (about 10^5 Ci). The GRB instrument would be the first cosmic gamma-ray burst detector to have to operate in this unfavorable background environment. To minimize the interference from the RTG, the sensors had to be mounted on the magnetometer boom, and were required to be essentially amagnetic. (More precisely, the remnant field could not exceed 2 x 10^-5 G at 25 cm.) Finally, the mass and power allocations for the GRB experiment were small compared to inner planet missions-2 kg and 2.6 W, respectively. Scientific Objectives --------------------- The Ulysses solar X-ray/cosmic gamma-ray burst instrument (acronym: GRB) has three main scientific objectives. The first is the study and monitoring of solar flare X-ray emission. The second is the detection and localization of cosmic gamma-ray bursts. The third is the in-situ detection of Jovian auroral X-radiation. Jovian X-radiation was first detected by using the Einstein satellite. X-rays in the 0.2-3 keV band were imaged with 4'' resolution, and provided evidence that the sources of X-radiation were the Jovian north and south auroral zones. The origin of the X-rays could have been either electron bremsstrahlung in the Jovian upper atmosphere, or characteristic line emission from atmospheric atoms excited by heavy ions precipitating from the Io torus. These two models make very different predictions about the hard X-ray flux in the Ulysses GRB energy range. References: ======== Dennis, B., Solar hard X-ray bursts, Solar Phys., 100, 465-490, 1985. (https://doi.org/10.1007/BF00158441) Dennis, B., Solar flare hard X-ray observations, Solar Phys., 118, 1-2, 49-94, 1988. (https://doi.org/10.1007/BF00148588) Hurley, K., in Cosmic Gamma Rays, Neutrinos, and Related Astrophysics, NATO ASI Series C 270, M. Shapiro and J. Wefel Eds., Kluwer Academic Publishers, Dordrecht, p. 337, 1988. (https://doi.org/10.1007/978-94-009-0921-2) Hurley, K., in Fourteenth Texas Symposium on Relativistic Astrophysics, Ann. N.Y. Acad. Sci. 571, E.J. Fenyves Ed., p. 444, 1989. Hurley, K., The Ulysses Solar X-ray/Cosmic Gamma-ray Burst Experiment, in Gamma-Ray Bursts: Observations, Analyses and Theories, Edited by C. Ho et al, p. 273, Cambridge Univ. Press, Cambridge, England ,1992. Hurley, K., M. Sommer, J.-L. Atteia, M. Boer, T. Cline, F. Cotin, J.-C. Henoux, S. Kane, P. Lowes, M. Niel, J. Van Rooijen, and G. Vedrenne, The solar X-Ray/cosmic gamma-ray burst experiment aboard Ulysses, Astron. Astrophys. Suppl. Ser: 92, 401-410, 1992. Hurley, K., M. Sommer, J.-L. Atteia, M. Boer, T. Cline, F. Cotin, J.-C. Henoux, S. Kane, P. Lowes, M. Niel, J. Van Rooijen, and G. Vedrenne, The solar X-Ray/cosmic gamma-ray burst experiment aboard Ulysses, Astron. Astrophys. Suppl. Ser: 92, 401-410, 1992. Metzger, A., D. Gilman, J. Luthey, K. Hurley, H. Schnopper, F. Seward, and J. Sullivan, The Detection of X-Rays from Jupiter, J. Geophys. Res., 88, 7731, 1983. (https://doi.org/10.1029/JA088iA10p07731)