V. F. Polcaro

A large area telescope for balloon-borne hard X-ray astronomy

Abstract A balloon-borne hard X-ray telescope is described that has been designed to make highly sensitive observations of cosmic sources in the energy range 15 to 300 keV. The payload is characterized by a combination of NaI(Tl) based detector of a novel design and spectroscopic proportional counters, providing a total sensitive area of 5000 cm2 and a 1 standard deviation sensitivity at the level of about 4 × 10−6 photons cm−2 s−1 keV−1. All of the telescope sub-systems are described including the micro-processor based orientation platform that provides a pointing stability of better than 10 arc min. The physical characteristics of the detectors are included along with a summary of the telescope performance during a balloon flight in 1982.

Low-flux hard X-ray observation of Cygnus X-1

The black hole candidate Cygnus X-1 was observed at a low flux level on 1985 August 5 with the POKER experiment in the hard X-ray range. During the same flight, the Crab Nebula was also observed as a in-flight calibration source, and the spectral results are reported. The measurements shows a low flux for Cygnus X-1. The photon spectrum is well described by a single power law, with a photon index of α = 1.87 and an intensity of 2.57 × 10 -3 photons/(cm 2 × s × keV) at 50 keV, corresponding to 1.11 Crab.

An imaging escape gated MWPC for hard X-ray astronomy

Abstract A scientific forward step in the hard X-ray and soft gamma-ray astronomy will only be possible with the use of a new generation of space borne instruments. Their main characteristics have to the two-dimensional imaging capability over a large collecting area and the fine spectral resolution in order to discriminate between the weak signal coming from cosmic sources to be detected and the strong background induced by cosmic rays, in the space environment, on the detector. To reach this goal we have developed a new hard X-ray position sensitive proportional counter operating with the escape gate technique in the range 15–150 keV, to be used together with a pseudo-random coded mask in order to obtain sky images. The detector is a high pressure (5 bar) xenon-argon-isobutane filled chamber with a spatial resolution of 30 × 2 mm and a spectral resolution of 5% at 60 keV on the sensitive area of 3000 cm 2 .

The position sensitive low energy detector on board the ZEBRA telescope

In order to improve the low energy capability (15 ÷ 150 KeV) of the balloon borne “ZEBRA” low energy gamma imaging telescope (150 KeV-20 MeV), a large area, high spectral resolution (5% at 60 KeV), low background detector has been designed and is now under development. It consists of two MultiWire Spectroscopic Proportional Counter (SPC), escape gated, that have a sensitive area of 6000 cm2, and are placed above the large area array of sodiumiodide position sensitive elements.

A large area multitechnique experiment for hard X-ray astronomy

A balloon-borne multitechnique large-area experiment comprising two co-aligned detectors (3200 sq cm NaI and 1800 sq cm multiwire proportional counters) is described. The NaI array is an actively shielded scintillation device designed to operate over photon energies of 20 to 300 keV. The telescope comprises eight modules, each consisting of a 6-mm-thick NaI crystal that is actively shielded over the lower 2 pi steradians by a 5-cm-thick NaI(Tl) crystal. The two crystals are optically isolated and the scintillation light from the primary crystal is collected by means of a diffusive light collection system that is approximately 10 cm high and is set below the collimators. It is noted that each diffusion box is viewed by two photomultipliers set in electronic coincidence. This minimizes the effects of tube noise and raises the uniformity of response and the energy resolution of the unit. In addition, the shape of the diffusion box is designed to maximize the energy resolution of the telescope so that a typical value at 60 keV is 25 percent FWHM.

A model independent method to deconvolve hard X-ray spectra☆

Abstract A general purpose method to deconvolve the energy spectra detected by means of the use of a hard X-ray telescope is described. The procedure does not assume any form of input spectrum and the observed energy loss spectrum is directly deconvolved into the incident photon spectrum, the form of which can be determined independently of physical interpretation of the data. Deconvolution of the hard X-ray spectrum of Her X-1, detected during the HXR 81M experiment, by the model independent method is presented.

The POKER experiment: A 10,800 cm2 MWPC's array payload for hard X-Ray Astronomy

Abstract In this paper the POKER-HXR81M hard X-Ray payload is described. The instrument, designed and built at the Istituto di Astrofisica Spaziale of Frascati, is a very large array of MultiWire Proportional Counters (MWPC) devoted to stratospheric observations of cosmic sources in the field of hard X-Ray Astronomy. The payload basically consists of four passively collimated MWPCs having a geometric sensitive area of 2,700 cm2 each with an efficiency higher than 10% in the operative range 15–200 KeV (80% at 60 KeV) with a square field of view of 5° × 5° FWHM. The overall spectral resolution is 13% at 60 KeV. The four MWPCs are filled with a very pure gas mixture of Xenon-Argon-Isobuthane at high pressure (3 bars). This experiment has been successfully flown during summer 1981 from the Milo balloon facility (Sicily, Italy). The performances of the payload and the preliminary results obtained during the 17 hours flight are discussed.

Long duration hard X-ray transatlantic payload

Abstract This note describes the HXR80M large area hard X-Ray Astronomy experiment. The payload is scheduled for a flight on board of a transatlantic balloon to be launched the next July from the Milo Base (Sicily), in the framework of the CNR experimental transatlantic campaign. The detectors are two Multiwire Spectroscopic Proportional Chambers (MWSPC) having 2,700 cm 2 sensitive area each. The two detectors are filled with an extremely pure Xenon-Isobutane mixture (impurity less than 1ppm) at high pressure (3–6 Atm) in order to obtain good spectral resolution and high efficiency. The field of view of the MWSPCs is limited by an array of three collimators each, having respectively 8°×8° and 5°×5° FWHM. The on board data handling is performed by microprocessor controlled electronics. In particular a micro Multichannel Analyzer (μMCA) is employed to obtain the spectrum of the detected photons. The scientific and housekeeping data are send to ground through a 1.2 Kbit PCM HF Telemetry link. The scientific aim of the experiment is the survey of the sky belt around the 38th parallel and in particular the observation of faint galactic objects and galactic binary systems in the range 15–200 keV.

ATTITUDE CONTROL SYSTEMS FOR SCIENTIFIC BALLOON PAYLOADS

In this paper we describe two stabilization systems developed for balloon borne payloads in X-ray astronomy experiments. One of them was employed in a 19 hours transmediterranean flight during summer 1978. The gondola, with a two stages pointing system was at lift-off about 300 kilos; the pointing requirement was 0.5 degrees precision. The control loop and the dynamical stability of the system are described and the in-flight performance is discussed.

A two-dimensional position-sensitive spectroscopic proportional counter for balloon-borne hard X-ray astronomy

Abstract A new design of position sensitive spectroscopic proportional counter is described, for use in a balloon borne hard x-ray telescope. Initial position and spectral resolution data from a one-dimensional laboratory prototype are reported. With this device, the final telescope will have an angular resolution of better than 10 minutes of arc.