LIME (Large-Area Imaging Mwpc Experiment): A High Resolution Space Borne Telescope

Abstract

The HEAO1 A4 satellite hard X-Ray sky survey, performed in the late '70s, has discovered a crowded and complex hard X-Ray sky in the range 10 180 keV. This intrigued scenario has been recently confirmed by high quality balloon borne experiments. These experiments in spite of their good spectral capability have been generally unable to provide good positional resolution and large sky coverage because of the use of passive collimators with wide field of view (f.o.v.) (typically 3 ÷ 15 degree). It is now evident the scientific need for a new generation of hard X-Ray instruments providing high imaging and spectral resolution over a wide energy range to study the spectral behaviour of different classes of cosmic sources and to identify these X-Ray emitters with their counterparts at optical, infrared and radio wavelenghts. In this note we will describe a new type of position sensitive MultiWire Proportional Counter (MWPC) recently designed and built at the prototype level in our Institute. This detector, expected to be fully operational in two years, will be assembled with a coded mask, employed as the imaging device, and flown on-board a balloon borne experiment as a high-resolutionwide-angle hard X-Ray telescope. The main scientific goal is to produce sky images in the range 15 + 180 keV with arcminute angular resolution, good spectral resolution (λ/Δλ=20) and milliCrab sensitivity, during a typical observation time of 10⁴ seconds. A space qualified version of this instrument operative in the range 2.5 ÷ 180 keV has been proposed on-board the Soviet mission "Spectrum X-Famma" expected to fly in the mid '90s.