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The hard X-ray spectrum of Her X1 was measured for the first time with a high-resolution (1.4 keV FWHM) germanium spectrometer (LEGS: GSFC/Saclay collaboration). The observation was performed near the peak of the 0B state in the 35 day cycle and 1.24 s pulsations were observed between the energies of 20 keV and 70 keV. The best fit energies are 35 keV for an absorption line and 39 keV for an emission line. These are significantly lower energies than those derived from previous experiments.
The GRASP mission (Gamma-ray Astronomy with Spectroscopy and Positioning) is currently under study as an ESA space astronomy mission to be launched in the mid 90's. GRASP is designed as a high quality spectral imager (E/ΔE ≈ 500 at 1 Mev) with positioning to the arc minute level within a large field of view (≈7°) which operates over a wide spectral range (30 Kev-100 Mev) with a 3σ sensitivity of typically 10 mcrab or better over the entire operational range within an observational period of ≈105 seconds. In this paper, we will mainly discuss the capability of the instrument with respect to the study of both point source and diffuse source measurements of the galactic center region.
The transient X-ray source GRS 1915+105 was discovered in August 1992 with the GRANAT/WATCH all-sky monitor (Castro-Tirado et al. 1994). Subsequent VLA observations from March through April 1994 led to the discovery of apparent superluminal motion in a pair of radio condensations moving away from the compact radio core (Mirabel & Rodriguez 1994). These jet-like features are interpreted as a bipolar outflow with bulk velocity ~ 0.9c. Although no optical counterpart has been observed, due to the heavy extinction in the Galactic plane, and therefore not enabling measurements of the mass of the compact object, the hard X-ray spectrum and high luminosity (~ 1039 erg s−1), extreme variability in the X-ray light curve and the relativistic jets make GRS 1915+105 a strong black hole candidate.
GX 339–4 has been monitored over a period of two and a half years with MOST and ATCA to investigate the flux variations and spatial structure of its radio emission. The data are summarized and discussed.
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