Hard X-ray astronomy with balloons

The hard X-ray studies of cosmic X-ray sources carried out with the balloon-borne instruments launched from Hyderabad (India) during 1968-1990 period are discussed. Advantages of making hard X-ray astronomy observations from Hyderabad are pointed out and the X-ray telescopes used in these studies are briefly described. A summary of the important results obtained from these studies on the galactic binary X-ray sources, a few extragalactic objects and the diffuse cosmic X-ray background, is presented. The important results include detection of hard X-ray flares in Sco X-1 and Cyg X-1, 4.8 hr intensity modulation in Cyg X-3, hard X-ray pulsations in the X-ray pulsars, energy spectra of Cyg X-1, Her X-1, 3C 273 and the diffuse Cosmic X-ray background, the correlated optical and hard X-ray intensity variations and the size of the hard X-ray emitting region in the Crab Nebula. Future hard X-ray studies planned to be carried out from Hyderabad are briefly described.