X-RAY OBSERVATORY

The X-ray observatory was composed by two independent X-ray detectors. The first one was an active collimator telescope that comprised a 2 mm thick X-ray detection scintillator, shielded by at least sixteen mean free paths of scintillator (at 100 keV) in all directions other than those within a conical viewing angle of 5º. The pulses from the X-ray detection scintillator WEre analysed by a 16 channel pulse height analyser, the upper and lower energy limits being 7 and 167 keV and each channel having a width 10 keV. The total sensitive area of this detector was 54,3 cm2. The temporal stability of the energy calibration of the complete detection system WAs monitored throughout the flight by introducing a radioactive source of Gadolinium-153 into the detector viewing cone for 60 seconds every 17 minutes.

The second detector was a graded shield telescope comprised by a Pb-Ag-Cu graded shield and a scintillating polytoluene anticoincidence shield, surrounding a 19 cm diameter, 3 mm thick CsI(Tl) scintillation detector. The sensitive area was 220 cm2. The pulses from this X-ray detector were sorted into four contiguous energy channels set at 30-40, 40-50, 50-60 and 60-80 keV. It had a rectangular field of view of 10º x 30º.

The two telescopes were inclined to the vertical (by 32º and 43º respectively) and pointed in the same azimuthal direction. Two orthogonal fluxgate magnetometers were used to determine the azimuthal pointing direction of the telescopes during the flight.

Balloon launched on: 2/29/1968 at 4:15 EAT
Launch site: HIBAL - Balloon Launching Station, Mildura, Victoria, Australia  
Balloon launched by: ABLS Mildura
Balloon manufacturer/size/composition: Zero Pressure Balloon  
Flight identification number: MIL-I-68
End of flight (L for landing time, W for last contact, otherwise termination time): 2/29/1968

The aim of the flight was to study the properties of a number of celestial objects near the galactic centre. Significant X-ray fluxes were observed from five X-ray objects, and upper limits have been established for four others.

• Spectral Properties of the X-Ray Objects GX 3 + 1, GX 354-5 and Sco XR-1 Nature, Volume 219, Issue 5159, pp. 1124-1127 (1968)
• The extension of celestial X-ray spectra to higher photon energies Proceedings of the Astronomical Society of Australia, Vol. 1, p.236
• Weak X-Ray Sources in the Southern Hemisphere Astrophysical Journal, vol. 167, p.479