Giuseppe Manzo

Status of the stellar x-ray polarimeter for the Spectrum-X-Gamma mission

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.

Stellar X-Ray Polarimeter: a focal plane polarimeter for the Spectrum X-Gamma mission

n this paper we describe 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 pho-toemission 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, an increase of two orders of magnitude over the x-ray polarimeters flown to date. 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.

Joint European x-ray monitor (JEM-X): x-ray monitor for ESA's INTEGRAL mission

JEM-X will extend the energy range of the gamma ray instruments on ESAs INTEGRAL mission (SPI, IBIS) to include the x-ray band. JEM-X will provide images with arcminute angular resolution in the 2 - 60 keV band. The baseline photon detection system consists of two identical, high pressure, imaging microstrip gas chambers, each with a collecting area of 500 cm2. They view the sky through a coded aperture mask (0.5 mm tungsten) at a separation of 3.4 m. The two detector boxes are formed from 2 mm thick stainless steel plate and are filled with 5 bar Xe. The field of view is defined by the collimator mounted on top of the detector. Each collimator consists of an array of bonded square tubes of Mo. The internal surface of these tubes is covered by a graded shield. The collimator provide also the support for the detector windows which are made out of 250 micrometer thick beryllium foils. The detector sensor elements consists of microstrip plates shaped as regular octagons with a diameter of 292 mm. The basic microstrip pattern is similar to the one chosen for the HEPC/LEPC detector system on SRG. The detector position resolution will be sufficient to ensure an angular resolution for JEM-X of better than 3 arcmin throughout the 2 - 60 keV band.

X-ray performance of the engineering prototype Stellar X-Ray Polarimeter

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.

Study of photoemission spectroscopy with polarized x-rays

Several recent experiments were conducted to study the x-ray induced photoemission from solids by polarized x rays for its potential application to stellar x-ray polarimetry. However, it was shown recently that the earlier observed polarization dependence of the secondary photoelectron yield was affected by spurious effects and no polarization dependence could be observed after these spurious effects had been eliminated. Here, we report our first measurement of the primary photoelectrons, i.e., photoelectrons with energy higher than 50 eV. We measured the primary photoelectron yield of a silicon sample as a function of the polarization state of the incident 2.69 keV x-ray beam. We observed that the change of photoelectron yield for different polarization states is especially pronounced around the no-loss photoelectron peaks. This polarization dependency can be explained by the angular distribution of photoelectrons from free atoms excited by polarized x rays. We discuss the experimental results and their implications.

THE POLARIZATION DEPENDENCE OF X-RAY PHOTOELECTRON YIELD OF A AU PHOTOCATHODE

We report a measurement of the total photoelectron yield of gold as a function of the incident x‐ray polarization. Polarized x rays with energies of 2.5, 2.7, and 4.0 keV were used to excite a gold photocathode at a glancing incidence angle between 5° and 50°. Contrary to a previous report, we found no measurable polarization dependence for all three x‐ray energies. We conclude that the modulation factor, i.e., the fractional change of the total yield when the polarization state is varied, is less than 4%.

SXRP: an X-ray polarimeter for the SPECTRUM-X-Gamma mission

SummaryTheStellar 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 hundreds of known X-ray sources. X-ray polarization measurements will allow us to constrain the physical mechanisms and the geometries 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.

Performance characteristics of the scientific model of the medium energy concentrator spectrometer on board the x-ray astronomy satellite SAX

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.

Performances of the imaging proportional counter of the stellar x-ray polarimeter

The Stellar X-Ray Polarimeter employs the same Imaging Proportional Counters for both the Bragg and the scattering stage. We show the main characteristics of these detectors and their performances on the basis of tests on the Technical Constructive Model and on the Engineering Models.

Performance characteristics of the medium energy gas scintillation proportional counter on board the Italian Dutch x-ray astronomy satellite SAX

The technological development of the Medium Energy Gas Scintillation Proportional Counter (MEGSPC), a part of the scientific payload of the Italian-Dutch X-ray Astronomy Satellite SAX, is presented. The detector and the experimental setup are briefly described and its detector performance characteristics are given. Experimental findings on the background resolution and spatial resolution are reported and the background rejection is discussed.