THE ON-GROUND CALIBRATION OF THE FLIGHT MODEL OF THE HPGSPC ONBOARD THE SAX SATELLITE - CALIBRATION SET-UP AND PRELIMINARY-RESULTS

The High Pressure Gas Scintillation Proportional Counter (HPGSPC) is o ne of the Narrow Field Instruments of the Italian-Dutch X-ray astronom y satellite SAX. Sensitive in the hard X-ray band (4-120 keV), with a very good energy resolution, the HPGSPC is well suited for studying in detail the cyclotron features present in the hard X-ray spectrum of s ome celestial sources. The scientific calibration of the flight model of the HPGSPC took place at the LABEN premises (Vimodrone-Milano) duri ng October and November 1994. In this paper we briefly describe the on -ground instrument calibration system and we report some preliminary r esults that show the performances of both single/double event and posi tion reconstruction/energy correction onboard processing. Preliminary results concerning the energy resolution and energy linearity are repo rted too.