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In the following paper we describe an event position reconstruction and energy correction technique that is being implemented on the High Pressure Gas Scintillation Proportional Counter (HPGSPC), that will be flown aboard the Italian Satellite for X-ray astronomy, SAX. We discuss how this technique will greatly enhance the spectroscopic performances of the detector and we report some results regarding the full area energy resolution of the scientific model of the HPGSPC.

The Stellar X-ray Polarimeter (SXRP) is a focal plane instrument which will be flown on the SPECTRUM-X-Gamma mission in 1993. The polarimeter is composed of two separate instruments: the first exploits the dependence on the polarization of the Bragg reflection from a graphite crystal, and of the Thomson scattering from a metallic lithium target. The second instrument makes use of the recently discovered polarization dependence of X-ray photoemission from CsI. The SXRP will permit sensitive measurements of several classes of galactic X-ray sources, such as X-ray pulsars, black-hole candidates and supernova remnants. Moreover, and for the first time, SXRP will be able to perform highly sensitive measurements of the brightest extragalactic sources.

We report results from multifrequency observations of the X-ray source 4U1700+24/HD154791. This source was observed simultaneously with the EXOSAT and IUE satellites on March 25, 1985, and it is continuously monitored in the optical band at the Bologna Astronomical Observatory since July 1984. Our observations show source features which are different from those measured during previous observations. The X-ray spectrum is significantly softer than in previous measurements, and much more absorbed; high excitation lines in UV spectra (C IV and N V) have disappeared; the optical spectrum, despite a fairly good photometric stability of the M giant HD154791 in V and B bands also shows differences with respect to previous observations. We discuss our results in the framework of both a binary model and a coronal model. We point out that our observations strengthen the hypothesis that the X-ray emission is due to mass accretion onto a compact object orbiting around the M giant star HD154791.

A description of one of the experiments on board the Italian X-ray Astronomy Satellite SAX is presented. The principle of operation and the technological problems are discussed in some detail.

The high pressure gas scintillation proportional counter (HPGSPC) is one of the narrow field instruments onboard the Italian Dutch mission for x-ray astronomy SAX. Sensitive in the 4 - 120 keV band the HPGSPC will investigate all categories of astrophysical sources emitting in the not yet well studied hard x-ray domain with a special emphasis on the cyclotron line features that are present in the hard x-ray spectrum of many celestial sources. The on-ground calibration of the flight model of the HPGSPC was carried out at Laben, Italy during October/November 1994. In this paper after describing the flight model of the HPGSPC instrument, we report preliminary results on its spectral capabilities and background rejection efficiency.

The performance of the engineering prototype Stellar X-Ray Polarimeter (SXRP) has been evaluated. One hundred percent polarized monochromatic x rays at 2.6 keV and 9.7 keV were used to measure the response of the instrument in the energy bands of the graphite and lithium polarizing elements, respectively. On-line analysis showed that the respective depths of modulation are 96% ad 70% as expected. Irradiating SXRP with broadband unpolarized x rays in the energy band 2 - 17 keV demonstrated that the level of spurious modulation inherent in the instrument is less than 3%. Up-to-date results are presented and compared to the predictions of Monte Carlo simulations.

The Stellar X-Ray Polarimeter (SXRP) uses the polarization sensitivity of a graphite Bragg crystal and a lithium Thomsom scattering target to measure the polarization of X-rays from astrophysical sources. The SXRP is a focal plane detector for the Soviet-Danish SODART telescopes which will be launched on the Soviet Spectrum-X-Gamma mission. The SXRP will be the third orbiting stellar X-ray polarimeter, and should provide an order of magnitude increase in polarization sensitivity over its predecessors.

We present the performance characteristics of a High Tech scientific model of the High Pressure Gas Scintillation Proportional Counter (HPGSPC) that has been developed as a prototype detector for the Italian X-ray Astronomy satellite SAX. We give some insight on the technology employed and we give an outline of one of the main areas of interest for the HPGSPC in the framework of the SAX mission.

The Stellar X-ray Polarimeter (SXRP) will be mounted on the focal plane of one of the two SODART telescopes aboard the Russian mission Spectrum-X-gamma. The SXRP employs the same Imaging Proportional Counters for both the Bragg and the scattering stages. An account is presently given of the main characteristics of these detectors and their performance, on the basis of tests at the technical-model and engineering model levels of development.

The scientific model of the SAX Medium Energy Gas Scintillation Proportional Counter has been tested at the PANTER X-ray facility in Munich. For part of the test the detector has been coupled to a representative reduced model of the SAX concentrators model. The results from the tests on both the detector and the detector/mirror assembly are within the expected performances. We have measured an energy resolution of about 8% (FWHM) and an angular resolution (on axis) of 1.3 arcminutes (HPR) at 6.4 keV.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Studies of the polarization dependence of the photoelectric effect produced by soft X-rays from CsI indicate that the geometrical effects in these experiments can often mimic the polarization signature. This paper presents a detailed calculation of these geometrical effects that are produced when the X-ray beam is not precisely aligned on a rotatable plane photocathode. The experimentally observed geometrical effects were used to precisely determine the realignment of the incident beam of polarized X-rays on a rotatable photocathode. The results allow determinations of the true polarization dependence of the photoemission from CsI. It is shown that the photoelectric effect in CsI depends on the polarization state of the X-rays.

We describe an X-ray polarimeter which will be flown on the SPECTRUM-X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a Cesium Iodide photocathode. These three processes allow polarization measurements over an energy band of 0.3 keV to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will allow us to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

This paper describes an X-ray polarimeter that will be flown on the Spectrum X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a cesium iodide photocathode. These three methods allow polarization measurements over an energy band from 0.3 to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will make it possible to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

Cygnus X-3 was observed with the GSPC on board EXOSAT on several occasions, one observation lasting for 7 orbital cycles. The width W and centroid energy E of the iron emission feature near 6.7 keV show a smooth, correlated, sinusoidal-type modulation, the iron line being widest and E being lowest just before X-ray maximum. The line profile may show a low-energy wing, but apart from this does not deviate strongly from a symmetric, Gaussian-type shape. The continuum at higher energies than the line is not completely smooth, but shows ’bumps’ which remain stable in time. Two possible explanations are discussed for the correlated variation of E and W as a function of orbital phase.

The in-orbit performance of the EXOSAT gas scintillation proportional counter spectrometer is presented. The background rejection capability in the EXOSAT deep orbit is examined as well as the overall detectors response. Typical examples of the spectra from cosmic X-ray sources show that this new type of detector will make a significant advance to the field of medium energy broad band X-ray spectroscopy.

A position sensitive gas scintillation proportional counter is presented for use as a broad band spectrometer in the focal plane of an imaging X-ray telescope. The 7 cm diameter detector has an on-axis position of ~ 2.5 mm and an energy resolution of ~ 10% for 6 keV X-rays. Design improvements are outlined which should provide a position resolution below ~ 1 mm at 6 keV over a useful aperture of ~ 8 cm. Such a detector, can, in conjunction with a suitable telescope, perform a spectral mapping in the range 0.1 - 6 keV of extended objects such as clusters of galaxies and supernova remnants with medium spatial resolution.

The determination of the optimum electrical parameters of a spherical electric field gas scintillation spectrometer for X-ray astronomy is described. Detailed measurements using a collimated 55Fe 5.9 keV X-ray source are presented leading to trade-offs of drift field, shaping and scintillation field in an endeavour to provide a uniform response in terms of energy and time resolution over the full aperture of 314 cm2. The optimized uncollimated energy resolution at 6 and 60 keV was 11.0 and 4.5% fwhm respectively. The total background rejection efficiency for 60Co gamma ray induced events was 97 and 70% in the energy range 1–10 and 1–60 keV respectively. Finally design improvements which yield and energy resolution as low as 7.5%K at 6 keV are outlined.

The First Spacelab Flight - scheduled for September 1983 - will carry a multidisciplinary payload intended to demonstrate that valuable scientific results can be achieved with such short duration missions. The payload complement includes a spectrometer to undertake observations of the brighter cosmic X-ray sources. The primary scientific objectives of this experiment are the study of detailed spectral features in cosmic X-ray sources and their associated temporal variations over a wide energy range from about 2 keV up to 80 keV. The instrument based on the gas scintillation proportional counter, will have an effective area of some 180 cm2 with an energy resolution of ∼ 9% FWHM at 7 keV. The key performance parameters of the instrument, which include calibration results and the sensitivity of the planned observations, are discussed.

Experimental results obtained from a new, position sensitive, gas scintillation proportional counter are presented. The counter, for use in X-ray astronomy as a focal plane instrument in conjunction with a grazing incidence imaging telescope, features a useful aperture of ~ 7 cm, a two-stage scintillation region and a seven photomultiplier tube Anger camera read-out system. An energy resolution of ? 20% FWHM at 1.25 keV (< 10% at 6 keV) and a position resolution of 900 ?m at 6 keV at the centre of the useful aperture are achieved.

The young supernova remnant Cas A has been observed with the imaging proportional counter (PSD) of the EXOSAT observatory. High quality spatially resolved, spectral data allow for the first time the determination of the temperature structure of the remnant. Preliminary results on the distribution of temperature and emission measureover the remnant are presented.

Results are presented on the development of a position sensitive gas scintillation proportional counter for use in high energy X-ray astronomy. This detector has a higher background rejection efficiency and a better energy resolution above 35 keV than conventional gas scintillators, gas proportional counters and crystal scintillators. These improvements arise directly fran the application of a discrimination technique which makes use of the detection of the fluorescent Xenon K shell photon emitted in most interactions involving the photoabsorption of genuine X-rays with energies greater than the K shell binding energy. Detectors incorporating this technique, and also having a position sensing capability to reject the induced Compton electron background fran the detector walls, will provide unique information on the spectral characteristics of cosmic X-ray sources. Such characteristics include high energy cyclotron lines fran neutron stars. The inherent imaging properties of these detectors when operated at high X-ray energies are also investigated. Such a detector when used in conjunction with a coded aperture mask will form a camera with an imaging capability of a few arc minutes at X-ray energies beyond the practical range of grazing incidence telescopes.

Results are presented on a background rejection technique suitable for xenon gas filled detectors measuring X-rays above 35 keV. The technique involves the separate detection of both the xenon K shell fluorescent photon, emitted in most interactions involving the photoabsorption of high energy X-rays above 34.5 keV, and the residual event from the initial photoabsorption. This technique when applied to gas scintillation proportional counters filled with 1 atm xenon yields a background rejection efficiency of ∼97.3% and an energy resolution of ∼2.5% at 60 keV.

The First Spacelab mission, launched on Space ShuttleFlight STS-9 in November 1983 carried a multidisciplinary payload which was intended to demonstrate that valuable scientific results can be achieved from such short duration missions. The payload complement included a spectrometer to undertake observations of the brighter cosmic X-ray sources. The primary scientific objectives of this experiment were the study of detailed spectral features in cosmic X-ray sources and their associated temporal variations over a wide energy range from about 2 up to 30 keV. The instrument based on the gas scintillation proportional counter had an effective area of some 180 cm2 with an energy resolution of ∼9% at 7 keV.

Results are presented on the performance of a large area gas scintillation proportional counter (GSPC) experiment for application as a spectrometer in X-ray astronomy. Two such counters will be launched on an Aries sounding rocket in 1979. This experiment has a total collecting area of 630 cm2, and an energy resolution of 11% for 6 keV X-rays. The intrinsic background rejection capability with the aid of burst length discrimination was ~ 80% for an X-ray acceptance of 80% at 6 keV.

EXOSAT CMA and GSPC observations of the Perseus Cluster of galaxies are reported. The soft X-ray image data confirm the earlier Einstein Observatory results in terms of the density distribution radially outward from NGC1275. We have used the GSPC spectral data at higher energies to study the strength of the X-ray continuum and of the Fe line emission over the cluster. An asymmetry is found in the distribution of the hot gas around NGC1275, which is consistent with the E-W direction of the ellipticity discovered at soft X-rays by the Einstein Observatory.

The High Pressure Gas Scintillation Proportional Counter (HPGSPC), one of the experiments on board of the Italian-Dutch X-Ray Astronomy Satellite SAX, is a large area (450 cm2), xenon filled (5 atm.), high energy resolution (3% at 60 keV) detector sensitive in the energy range from 4 to 120 keV. In the paper we give a general description of the characteristic of the experiment. Some effort is dedicated to illustrate the on board energy correction algorithm required for preserving the potentially good full area energy resolution .

In this paper we describe the High Pressure Gas Scintillation Proportion Counter, one of the Narrow Field Instrument of the X–ray astronomy satellite BeppoSAX. Sensitive in the 4-120 keV band, the HPGSPC will study all astrophysical sources emitting in the poorly studied hard X–ray band. The design and performances of the instrument are reported together with results of the on–ground calibration data analysis.

A hollow cylindrical proportional counter is the best choice for an X-ray polarimeter based on the Thomson scattering. Here we report on the results of Montecarlo simulations performed to optimize the geometrical configuration of such a polarimeter, conceived as a focal plane instrument of an X-ray telescope. We also present the design characteristics of a prototype of a cylindrical proportional counter, presently under testing in our laboratories.