SIXE: An x-ray experiment for the MINISAT platform

SIXE (Spanish Italian X-ray Experiment) is an X-ray detector with geometric area of 2300 cm(2), formed by four identical gas-filled Multicell Proporti onal Counters, and devoted to study the long term spectroscopy of selected X-ray sources in the energy range 3-50 keV. The main characteristics of SIX E are: time accuracy of 1 microsecond, spectral resolution of 5% for E > 35 keV and 46/rootE% for E < 35 keV, continuum sensitivity (3 sigma in 10(5) s) of 2 x 10(-6) ph cm(-2) s(-1) keV(-1), and line sensitivity (3 sigma in 10(5) s) of 8 x 10(-6) ph cm(-2) s(-1). The size of the instruments and the requirements of the payload (weight 103 kg, full dimensions 660 x 660 x 45 0 mm(3), power budget < 60 W, on-board memory 2 Gbits, telemetry rate < 100 kbps) make this experiment fully compatible with the MINISAT platform. The main scientific goal of SIXE is the study of short and long term variabili ty of some of the most important X-ray sources. To do that a few selected e xtragalactic and galactic X-ray sources will be selected to perform a dedic ated and extensive monitoring program. The mission will provide in this way the unique opportunity for the study of X-ray sources with a temporal accu racy of 1 microsecond all through the time range 10(-5) :10(7) s.