High-energy Astronomy Research Articles

ADVANCED X-RAY OBSERVATORIES

Since the discovery of the first X-ray sources in 1962 by the use of modest instruments flown on sounding rockets Giacconi et al. (1962), observations of cosmic X-rays have continued to provide a steady flow of information that has affected our view of virtually all astronomical phenomena. Correspondingly, an increasing share of the resources devoted to space sciences of many nations has been allocated to this new observing window. Within the past year the first satellite devoted to X-ray astronomy, UHURU, was launched by NASA followed by a second satellite launched by the Naval Research Laboratories. Within the next several years a number of small satellites devoted largely to X-ray astronomy SAS-C by NASA, UK-IV by Great Britain, and the ANS by the Netherlands will be flown, as well as individual experiments on such satellites as OSO. In 1975, NASA is planning to begin its High Energy Astronomy Observatory (HEAO) series based on the use of the Titan-3C launch

Cerenkov Light Collection in the High Energy Astronomical Observatory a Cosmic Ray Experiment

An improved Cerenkov counter for the High Energy Cosmic Ray Experiment on the first High Energy Astronomy Observatory will make the resolution between different nuclei much better. A more UV reflecting paint and improved radiator and PMT positioning should give us hoped for results.

Design of a Celestial Thomson-Scattering X-Ray Polarimeter

A general discussion of the scientific importance and status of stellar x-ray polarimetry is presented. A stellar x-ray polarimeter designed to fit into the bottom half of the NASA Orbiting Solar Observatory-I (OSO-I) wheel compartment or other similar spacecraft is described. In this design, the linear polarization is obtained as a function of energy. The sensitivity of the polarimeter in the 4 - 24 keV energy range was optimized with the aid of a Monte Carlo simulation computer program and is given for several important celestial x-ray sources. Estimates of sensitivity thresholds for a much larger polarimeter, suitable for flight in the NASA High-Energy Astronomy Observatory (HEAO), are also given. The minimum detectable polarization for several x-ray sources is given. For example, the minimum detectable polarization at the 99% confidence level for the Crab nebula in a 24-h observation time is 1.4% for an OSO polarimeter in a compartment (50 × 30 × 30) cm and 0.27% for a HEAO polarimeter in a compartment (100 × 100 × 30) cm. These satellite experiments are feasible and will yield significant polarization results which will have an important bearing on our understanding of x-ray source mechanisms.

HIGH‐ENERGY RADIATIONS FROM SPACE

Survey of past, current, and planned U.S. high-energy astronomy observation (HEAO) experiments in space, and review of their significance. It is shown that astronomical observations from spacecraft during the first decade of space flight, though they be few and modest, have provided a wealth of new results that are most exciting, and that suggest that the next 20 or 30 years of space exploration may write a new chapter in the history of astrophysics and astronomy as important as the chapters initiated by Galileo or by the five-meter telescope on Mount Palomar. Special attention is given to the planned HEAO-A and HEAO-B experiment series.

Lockheed space system will put observatory into circular orbit

A Lockheed circularizing system called the Orbiting Adjust Stage (OAS), will help place a High Energy Astronomy Observatory (HEAO) in a 200‐nautical‐mile circular orbit. The OAS fits atop the Titan IIID primary booster, and above the Orbit Adjust Stage is the observatory spacecraft. The OAS and its motor will remain attached to the observatory and will put it into a virtually perfect circular orbit, with a variance of less than two miles.

Instrumentation for the Measurement of High Energy Phenomena on NASA Spacecraft

High energy astrophysical observations supported by the National Aeronautics and Space Administration will be conducted primarily from the Small Astronomy Satellites (SAS) and the High Energy Astronomy Observatories (HEAO). At the present time, three Small Astronomy Satellites have been approved for flight. The first (SAS A) will carry a set of collimated proportional counters to conduct a high sensitivity, high spatial resolution, all sky survey for X-ray sources, to search for temporal variations in the source intensity, and to measure the spectral distribution of sources in the energy range 1 to 20 keV. The spacecraft will carry two collimator systems of 1 by 10 deg and 10 by 10 deg fullwidth. The proportional counters are gas-filled beryllium window tubes. SAS A is planned for launch in late 1970.

A New Instrument Concept for Gamma Ray Astronomy

A new instrument concept that utilizes the principle of the Total Absorption Shower Cascade (TASC) detector is proposed for gamma ray astronomy in space. Using the TASC detector to measure the gamma ray energy and wire chamber arrays to measure the incident angle, an instrument package designed to measure gamma rays having energies greater than 100 MeV is being proposed for a large satellite such as NASA's proposed High Energy Astronomy Observatory. The proposed instrument has a minimal flux sensitivity of 2 × 10-10 photons/cm2 sr sec which will allow gamma rays with energies up to 104 GeV to be measured. An energy resolution (FWHM) for the TASC detector of ~l percent at 10 GeV has been measured and an angular resolution of ~1 degree appears to be obtainable for the wire chamber arrays.

Servo systems for Cerenkov light receivers

The paper describes a variety of servo systems which have been developed for use with Cerenkov light receivers. Particular attention is devoted to the problem encountered in the high-energy γ-ray astronomy application, namely that the total background light within the field of view should be maintained constant during individual drift-scans or on–off comparison runs.Both filament lamps and midget fluorescent indicating lamps have been used as the active elements in the servo loops, and the systems have been operated either (a) from the phototube current or (b) from the counting rate at a selected pulse-height discrimination level. The characteristics of the various systems are discussed, in relation to the control factor, dynamic range, and stability. One of the systems developed was fast enough to respond to stellar atmospheric scintillations in the frequency range d-c. to 1 kHz.A servo system of a different type is also described, in which the sensitivity rather than the background light can be stabilized; in this way it was found possible to accommodate large variations of background light over long periods.