A precedent to the recently-discovered pulsed radio sources or ‘pulsars’ exists in our own solar system. Jupiter could be thought of as a very slow ‘pulsar’ having a period of about 10 h or 35 000 s. Like pulsars, this emission period is known to a high order of accuracy (about 1 in 106). One difference is that Jupiter emission is received over an appreciable part of this period (1/4 to 1/2 or more) compared with about 1/30 of a typical pulsar period (about 40 ms in 1.3 s). Both pulsar and Jupiter bursts have a microstructure of the order of milliseconds, suggesting similar sizes of instantaneous emission regions. In both, the intensity observed varies from period to period. Emissions from both have relatively strong circular-polarization components at times.

For the past six years astronomers have been regarding the universe through a new window—the X-ray window. In these six years this subject has experienced a ‘remarkable’ growth. In late 1966 workers from the Naval Research Laboratory (NRL) published a catalogue containing 35 X-ray sources. In my preparation for this report I have compiled a new catalogue containing only 22 sources (which I believe contains all of the presently confirmed X-ray sources). This early proliferation of ‘sources’ may be attributed to the exuberance of the experimenters or perhaps to a poor understanding of the laws of statistics. A simple calculation shows that, with this rate of decrease of ‘observable’ sources, X-ray astronomy will cease to exist as a subject in 1972!

This paper presents observations of weak X-ray sources at photon energies between 20 and 100 keV which were made during a balloon flight conducted from Mildura, Australia on 29 February 1968. Results obtained from Sco XR-1 and the Sagittarius region during this flight have been presented elsewhere, and here we report additional results obtained during a search of an area of sky in which several sources have been reported from rocket experiments at photon energies below about 10 keV. The detector used was an actively collimated and shielded NaI(T1) crystal, 2 mm thick and 54.3 cm2 in area. Incident photons were sorted into 16 energy channels between 7 and 167 keV (1.76 to 0.07 Å). The collimator field of view was 8°FWHM; the telescope axis was fixed at a zenith angle of 32° and its azimuth angle was varied by rotating the observatory below the balloon. This allowed the telescope to scan back and forth in azimuth across a source, the azimuth angle at any time being indicated by magnetometers.

During a recent balloon flight from Mildura, Australia, the region of the Galaxy between −10° < lII < +20°; −5° < bII< +5° was surveyed for high-energy X-rays of photon energy > 17 keV (λ < 0.7 Å) using an active collimation scintillation detector described elsewhere. The narrow opening angle of the telescope enables two sources to be resolved in this region of the sky. The position of one of these sources agrees well with the source GX3+1 observed at rocket wavelength by Bradt et al. while the other source is probably the same as that observed by Gursky et al. and designated GX−5.6. We present herein improved positional information for this latter source which hereafter will be designated GX354−5.

This paper reports results from a graded shield X-ray telescope experiment flown from Mildura, Australia on 29 February 1968. The experimental equipment also included the actively collimated telescope previously described. Certain preliminary results from this flight have been described elsewhere.

This paper presents the results of a measurement of the high-energy (E ≥ 17 keV) X-ray flux from Sco XR-1 extending to higher energies than has previously been reported. The measurement was made during a balloon flight launched from Mildura, Australia, on 29 February 1968. The X-ray observatory contained two independent X-ray detectors, one being similar in principle to the active collimator detector pioneered by Peterson et al., the other being basically similar to the graded shield detector developed by Boldt et al. Our two detecting systems are described in more detail by Buselli et al. and also in previous papers of this conference.

This paper presents a measurement of the diffuse cosmic X-ray background made during the balloon flight described in preceding papers and elsewhere. The data used for this paper were obtained with the actively shielded and collimated detector previously described. The geometric factor of the detector was 1.17 cm2 sterad.

In comparison with all other branches of astronomy, X-ray astronomy suffers from a relative dearth of image forming devices. No X-ray lens is known and image formation by reflection requires glancing incidence optics which have small fields of view and are extremely difficult to fabricate, even for the small apertures (about 2 cm2) now employed. The only other imaging device which has been successfully employed is the simplest of all, the pinhole camera. Pinhole cameras with resolutions better than 10−3 rad are easily constructed, but the apertures are very small—not greater than about 10−4 cm2. The new instrument described here is closely related to the pinhole camera and may be viewed as an attempt to overcome the aperture restrictions of this simple device.