NEW BALLOON-BORNE TELESCOPE SYSTEM TICAL MARK-II FOR HARD X-RAY ASTRONOMY

For the study of hard X-rays (18-150 KeV) from the celestial X-ray sources, NaI/CsI phoswich scintillator telescopes have been flown from Hyderabad during the last decade. The NaI(T1)/CsI(Na) scintillator phoswich with Pulse Shape Discrimination technique reduces the nan X-ray background by a factor 10 at balloon altitudes. The new telescope TICAL Mark-II with 1000sq.cm area [5 mm thick NaI(T1) and 50 mm thick CsI(Na) phoswich] had a sensitivity to detect a minimum flux of 2.2 x l0(-6) photons/sq.cm sec KeV in the energy range 18-150 KeV for 10(4) a exposure; this allows study of several bright active galactic nuclei, The telescope had a microprocessor-based tracking system to automatically follow celestial sources in elevation and azimuth according to a predetermined schedule. Several galactic X-ray sources, mostly binary pulsars, and the quasar 3C273 have been studied. The scintillator phoswich X-ray detector, the X-ray telescope and the electronic systems of the TICAL Mark II will be described.