Position Sensitive Proportional Counter Research Articles

A MULTIANODE POSITION-SENSITIVE PROPORTIONAL COUNTER FOR IN-AIR HIGH-RESOLUTION PIXE USING A CRYSTAL SPECTROMETER

A position-sensitive proportional counter (PSPC) for a wavelength-dispersive crystal spectrometer system has been constructed for high-resolution PIKE experiments in atmospheric air. This PSPC has seven resistive wire anodes. Each anode operates as one PSPC. Pulses from the anodes are converted into digital signals with a 512 × 7 channel charge-division analyzer. We can simultaneously obtain seven spectra. A computer software converts this 2D data set into one spectrum after adjusting the offset channels and conversion factors. The spatial resolution of this detector is somewhat larger than that of our single PSPC system previously developed, while its counting efficiency is seven times higher than that of the single one.

X‐Ray Spectral Survey of WGACAT Quasars. I. Spectral Evolution and Low‐Energy Cutoffs

We have used the WGA catalog of ROSAT Position Sensitive Proportional Counter (PSPC) X-ray sources to study the X-ray spectrum of about 500 quasars in the redshift interval 0.1-4.1, detected with a signal-to-noise ratio better than 7. We have parameterized the PSPC spectrum in terms of two effective energy spectral indices, αS (0.1-0.8 keV), and αH (0.4-2.4 keV), which allows for the different Galactic NH along the quasars' line of sight. We have used these data to explore the questions raised by the initial PSPC high-redshift quasar studies, and in particular the occurrence of low-energy X-ray cutoffs in high-redshift radio-loud quasars. We have also studied the emission spectra of a large sample of radio-loud and radio-quiet quasars and studied their differences. We find that low-energy X-ray cutoffs are more commonly (and perhaps exclusively) found in radio-loud quasars. Therefore, the low-energy X-ray cutoffs are physically associated with the quasars, and not with intervening systems, since those would affect radio-quiet and radio-loud equally. We suggest that photoelectric absorption is a likely origin of these cutoffs. The number of cutoffs in radio-loud quasars significantly increases with redshift rather than with luminosity. A partial correlation analysis confirms that αS is truly anticorrelated with redshift at the 99.9% confidence level, indicating evolution with cosmic epoch, and not a luminosity effect. Conversely, for αH the observed anticorrelation with redshift is mostly due to a strong dependence on luminosity. In radio-quiet quasars, we find marginal evidence for a flattening of αH (P = 4.5%), going from z 2.

A radio continuum study of the Magellanic Clouds

By comparing Parkes telescope radio surveys with the X-ray ROSAT All-Sky Survey (RASS) we have found 71 discrete sources of both radio and X-ray emission in the Large Magellanic Cloud (LMC). These 71 sources are mainly supernova remnants (SNRs) and SNR candi- dates (36), and background sources (27). For six of the sources we have no proposed identication and the other two are H ii regions. A source-intensity comparison of the radio and X-ray sources shows very little correlation, but we note that the strongest SNRs at both radio and X-ray frequencies are young SNRs from Population I. Six new LMC SNR candidates are proposed. From the radio flux density of the SNRs we have estimated the SNR birth rate to be one every 100 (20) yr and the star-formation rate (SFR) to be 0: 7( 0 :2) M yr 1 . A similar comparison was undertaken for the Small Magellanic Cloud (SMC), but instead of the RASS we used a roster of pointed observations made with the ROSAT Position Sensitive Proportional Counter (PSPC). This comparison resulted in 27 sources in common be- tween the Parkes radio and ROSAT PSPC surveys. Two

ITAL]Extreme[/ITAL] [ITAL]Ultraviolet[/ITAL] [ITAL]Explorer[/ITAL] Right Angle Program Observations of Cool Stars

The Extreme Ultraviolet Explorer (EUVE) Right Angle Program (RAP) obtains photometric data in four bands centered at ~100 A (Lexan/B), ~200 A (Al/Ti/C), ~400 A (Ti/Sb/Al), and ~550 A (Sn/SiO) during pointed spectroscopic observations. RAP observations are up to 20 times more sensitive than those in the EUVE all-sky survey. We present RAP observations of two dozen late-type stars: BD +03°301, BD +05°300, HR 1262, BD +23°635, BD +22°669, Melotte 25 VA 334, Melotte 25 1366, Melotte 25 59, Melotte 25 65, θ1 Tau, V834 Tau, GJ 2037, BD -21°1074, GJ 205, RE J0532-030, GJ 9287A, HT Vir, BD +46°1944, Proxima Cen, α Cen A/B, HR 6094, HR 8883, CPD -48°10901, and HR 8964. We derive surface fluxes from the Lexan/B and Al/Ti/C count rates and cataloged ROSAT Position Sensitive Proportional Counter (PSPC) data. The EUVE surface fluxes are reasonably correlated with surface fluxes calculated from PSPC measurements. The time variability of the sources has been examined. Most of the sources show no significant variability at the 99% confidence level. Flares were detected from the K7 V star Melotte 25 VA 334, the K3 V star V834 Tau (HD 29697), and the K3 + K8 Hyades binary BD +22°669. The BD +22°669 count rate at the peak of the flare is a factor of 6 higher than the quiescent count rate, with a peak Lexan/B luminosity of 7.9 × 1029 ergs s-1. The V834 Tau flare was detected in both Lexan/B and Al/Ti/C bands. The peak luminosity of the flare is 1.6 × 1029 and 8 × 1028 ergs s-1 for Lexan/B and Al/Ti/C, respectively.

Small‐Scale Variations in the \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\frac{1}{4}$ \end{document} keV X‐Ray Background along the Galactic Plane

Forty-two ROSAT Position Sensitive Proportional Counter pointed observations in the first quadrant (l ~ 4°-26°) of the Galactic plane are mosaicked in order to study the spatial structure of the X-ray-emitting gas in the Local Hot Bubble (LHB). X-ray intensity variations at various angular scales are examined in the 1/4 keV band, and degree-scale variations are detected. In the context of the LHB and the displacement model for the origin of the 1/4 keV band background, the hardness ratio, angular size, and magnitude of the intensity variations suggest that at the ±10% level there is an influence of a clumpy boundary structure superposed upon the emission from the uniformly distributed ~106 K plasma of the LHB interior. The possible origins of such a clumpy boundary structure of the LHB are discussed with Rayleigh-Taylor instabilities and clumping of the cooler interstellar medium at the boundary region being likely candidates.

The 1993 August Minioutburst of GRO J0422+32

We report on observations of the soft X-ray transient (SXT) GRO J0422+32 made with the ROSAT Position Sensitive Proportional Counter (PSPC) and the ASCA GIS and SIS X-ray imaging spectrometers during its 1993 August outburst. This event occurred approximately one year after the primary outburst of the source and was characterized by an X-ray-to-optical luminosity ratio much smaller than that typically seen in SXT outbursts or in steady, low-mass X-ray binaries. Our X-ray observations with the ROSAT PSPC, spread over 6.2 days and totalling 28.8 ks, combined with our archival analysis of 17 ks of ASCA observations, indicate an approximately 1 mcrab source that turned and subsequently back on over a 10 day period, with distinct spectral characteristics in each case. In addition to our analysis of the X-ray spectra, we report on optical photometry and spectroscopy bracketing the X-ray observations. It is noteworthy that the optical light curves remain approximately constant, at least in our data's almost daily sampling, during the turning and turning on sequence seen in the X-rays. Optical spectroscopy reveals large, asymmetric redshifted and blueshifted components in the double-peaked emission lines He II λ4686 and Hβ λ4861, which can be interpreted as evidence for a wind emanating from the secondary. The phasing of these shifts ruled out a wind originating from the disk. On the other hand, the X-ray power illuminating the star seems insufficient for driving such a wind. Comparisons are made with the primary (1992) outburst and decay phase of GRO J0422+32. Implications for X-ray reprocessing scenarios of the production of optical and UV emission and for other possible scenarios, such as advection-dominated accretion, are briefly considered. An upper limit to the quiescent X-ray luminosity is estimated using data acquired during the X-ray off state. A similarity between the X-ray-to-optical behavior of GRO J0422+32 during this minioutburst and previously documented optical-to-EUV behavior of certain SU Ursae Majoris system outbursts is noted. A physical interpretation of this analogous behavior, suggesting that the hot and cold branches of the S-shaped stability curve may be relatively closely spaced in GRO J0422+32, is offered.

ROSATPSPC Observations of 27 Near–Main‐Sequence B Stars

In this paper, we report on ROSAT Position Sensitive Proportional Counter (PSPC) observations of 27 near-main-sequence B stars made with unprecedented sensitivity. Contrary to the results of previous surveys, it is found that 75% of the sample stars are X-ray sources, albeit most at modest levels. The X-ray luminosities of the program stars range from 5.6 × 1027 up to 2.2 × 1032 ergs s-1. We find that LX/LBol decreases abruptly beyond about B0 and stabilizes at LX/LBol ≈ 10-8.5 by about B2, with seven nondetections at B2 and later. For the B0 and B1 stars, our modeling suggests that wind attenuation of the X-ray photons is significant, so that the emitted X-ray luminosity, corrected for this attenuation, actually exceeds 10-7LBol in some cases. Presumably, this situation is even more severe for O stars; thus, the well-known LX/LBol ≈ 10-7 law simply may be an artifact of the neglect of wind attenuation. The ROSAT PSPC observations of most of the B stars are very soft, with the notable exception of τ Sco (B0 V). The wind emission measure filling factors that we find for the very early B stars are rather large (roughly 0.1-1). This could be brought into line with theoretical calculations of the line-force instability, wind-shock mechanism if the mass-loss rates of these stars are a few times higher than theory currently predicts. However, the X-rays from stars later than B2 require filling factors greater than unity and thus cannot be produced by any radiation-driven wind-shock mechanism because there is simply not enough wind material to produce the observed X-rays. It is possible that mid- to late-B stars represent some kind of transition to, or hybrid of, wind and coronal X-ray mechanisms.

Faint Sources in theEUVESurvey: Identification of White Dwarfs, Active Late‐Type Stars, and Galactic Nuclei

We report the classification of 21 new extreme-ultraviolet sources from the recent catalog of Lampton et al. The optical spectra presented identify the objects as 14 active late-type stars (including two double active stars and a possible T Tauri star), three white dwarfs, and six active galactic nuclei (a Seyfert galaxy, the BL Lac object 1ES 1028+511 [=EUVE J1031+508], and four quasi-stellar objects). We have detected Ca II absorption lines in the BL Lac object and measured its redshift. Two of the white dwarfs are unusually massive (M > 1.1 M☉). Our sample of late-type stars includes five previously known high proper motion objects (EUVE J1004+503, J2244-332A,B, J1802+642, and J1131-346), of which one is the well-known flare star TX PsA (EUVE J2244-332B). We report an unusually high level of activity for the primary component of the TX PsA system (EUVE J2244-332A), which may indicate flare activity. The group of late-type stars is on average almost 3 mag fainter (⟨m⟩ ≈ 13) than the typical member of the Extreme Ultraviolet Explorer (EUVE) all-sky survey catalog. All Galactic and extragalactic objects were also detected in the ROSAT Position Sensitive Proportional Counter survey, and most are at the faint limit of the EUVE detectors. These new identifications substantially increase the total number of EUV-selected extragalactic sources.

X‐Ray Spectral Survey of WGACAT Quasars. II. Optical and Radio Properties of Quasars with Low‐Energy X‐Ray Cutoffs

We have selected quasars with X-ray colors suggestive of a low-energy cutoff, from the ROSAT Position Sensitive Proportional Counter (PSPC) pointed observations archive. We examine the radio and optical properties of these 13 quasars. Five out of the seven quasars with good optical spectra show associated optical absorption lines, with two having high Δv candidate systems. Two other cutoff quasars show reddening associated with the quasar. We conclude that absorption is highly likely to be the cause of the X-ray cutoffs, and that the absorbing material is associated with the quasars, not intervening along the line of sight. The suggestion that gigahertz peaked sources are associated with X-ray cutoffs remains unclear with this expanded sample.

X‐Ray Absorption toward the Einstein Ring Source PKS 1830−211

PKS 1830-211 is an unusually radio-loud gravitationally lensed quasar. In the radio spectrum, the system appears as two compact, dominant features surrounded by relatively extended radio emission that forms an Einstein ring. As the line of sight to it passes close to our Galactic center, PKS 1830-211 has not been detected in wave bands other than the radio and X-ray so far. Here we present X-ray data of PKS 1830-211 observed with ROSAT Position Sensitive Proportional Counter. The X-ray spectrum shows that absorption in excess of the Galactic contribution is highly likely, which at the redshift of the lensing galaxy (zl = 0.886) corresponds to NH=3.5−0.5+0.6×1022 atoms cm-2. The effective optical extinction is large, AV(observed) ≳ 5.8. When corrected for this additional extinction, the two-point optical to X-ray slope αox of PKS 1830-211 lies just within the observed range of quasars. It is argued here that both compact images must be covered by the X-ray absorber(s) that we infer to be the lensing galaxy (galaxies). The dust-to-gas ratio along the line of sight within the lensing galaxy is likely to be somewhat larger than for our Galaxy.

Precision Lattice Spacing Measurements Using X-Ray Cu KαDoublet

A precision method of measuring the lattice spacing difference by a sensitivity of 1 part in 10 7 is presented. The method uses the Kα doublet from one conventional X-ray tube as two beams with a position sensitive proportional counter in a double-crystal spectrometer. To achieve this sensitivity the device positioning the sample crystal parallel to the monochromator is used. The method is applied to the examination of the lattice spacing variations in silicon crystals containing 0.93 to 1.5×10 18 atoms/cm 3 of oxygen contents which are subjected to a two-step (low-high) annealing. The lattice spacing differences obtained for these samples are in the range of 10 -7 –10 -6 .

ROSATandASCAObservations of W50 Associated with the Peculiar Source SS 433

We report the observations of the X-ray lobes of the large Galactic source W50 associated with the two-sided jets source SS 433. The observations were made with the Position Sensitive Proportional Counter on board ROSAT. The eastern lobe has a knotty structure, with X-ray emission starting at ~15' from SS 433 and peaking at ~35'. Both thermal bremsstrahlung spectra with high temperatures (≥5 keV), as well as power-law spectra with flat photon index (Γ ~ 1-2), gave adequate fits. With ROSAT, we also detected an additional soft X-ray emission from the eastern lobe, at ~1° east of SS 433 and coincident with the radio ear. This region is associated with the terminal shock of the SS 433 jets. The western lobe has a similar morphology; however, the spectrum is softer, and no emission was found coincident with the western radio ear. We also report the observations of W50 with the Advanced Satellite for Cosmology and Astrophysics (ASCA), and combine the ROSAT and the ASCA data for a wide coverage of the spectra in the 0.1-10 keV energy range. We find that the spectrum from the brightest region (at ~35' from SS 433) requires an additional component to account for an excess of photons in the 1-3 keV band. The total X-ray luminosity from both lobes is ~1035-1036D25.5 ergs s-1. We discuss the origin of the X-rays in the model of emission from the supersonic jets of SS 433 interacting with the ambient medium, accelerating particles to very high energies, and producing a cocoon of hot shocked material. We present our interpretation in light of the correlation of X-ray emission with the map of W50 at other wavelengths.

Extreme Ultraviolet Explorer Optical Identification Campaign.III. A Southern Hemisphere Sample of Active Late-Type Stars and White Dwarfs

view Abstract Citations (9) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extreme Ultraviolet Explorer Optical Identification Campaign.III. A Southern Hemisphere Sample of Active Late-Type Stars and White Dwarfs Craig, Nahide ; Christian, Damian J. ; Dupuis, Jean ; Roberts, Bryce A. Abstract We present optical identifications of 30 previously unidentified extreme ultraviolet (EUV) and soft x-ray sources coinciding with the position of faint sources detected during the all-sky surveys of the Extreme Ultraviolet Explorer ({\euve}) in the 58-174 Angstroms (0.071-0.214 keV) band and of the \rosat\ Position Sensitive Proportional Counter (PSPC) in the 5-120 Angstroms (0.1-2.4 keV x-ray) band. We present low-resolution spectra of the possible optical counterparts of the x-ray and \euve\ sources obtained with 1.5 m telescope at CTIO in 1995 May and December and 1996 February. The optical counterparts for 23 sources are identified as late-type (dKe and dMe) stars, and 4 are identified as new DA white dwarfs. All spectra of sources identified as late-type stars show the Balmer series and Ca H and K lines in emission, indicating the signature of chromospheric activity. For the white dwarfs, the joint detection by the \rosat\ PSPC and the \euve\ Lexan band indicates that they have a low-abundance of metals and that their EUV emission is mostly attenuated by the local interstellar medium (ISM). Publication: The Astronomical Journal Pub Date: July 1997 DOI: 10.1086/118469 Bibcode: 1997AJ....114..244C full text sources ADS | data products SIMBAD (78) MAST (1)

High energy resolution PIXE with high efficiency using the heavy ion microbeam

An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam ( E < 6 MeV) with reasonable detection efficiency. The design of the spectrometer, such as detection geometry, detectable energy range and energy resolution, are described. This system was applied to high energy resolution PIXE analysis of Ti, SUS and Si with 2 MeV proton and 5 MeV Si 3+ focused or collimated beams. The best energy resolution was 2 eV for the Si Kα line.

ROSATPSPC Observation of the Northeast Region of the Vela Supernova Remnant. II. Spectral Analysis with a Nonequilibrium of Ionization Emission Model

We have developed a grid of nonequilibrium of ionization (NEI) models that depends on the electron temperature and ionization time and that is suitable for use in -tting X-ray spectra. Using this grid, we have carried out a spatially resolved spectral analysis of a ROSAT Position Sensitive Proportional Counter (PSPC) observation of the northeast shock region of the Vela supernova remnant on an angular scale of 10@ (D1.0 pc at the distance of the remnant). The adopted model passes the s2 test at the 95% con-dence level for 45% of the considered spatial bins, giving unexpectedly low values of the ionization time (log q D 0E 1y r cm~3). We discuss the possibility that this result may be due to a reduced contribu- tion from a line emission, which may be related to the locking of metals in grains. We also -nd signi-- cant temperature gradients on the scale explored, and we argue that they are correlated to interstellar matter inhomogeneities encountered by the shock front. The emission from the remaining 55% of the bins is incompatible with the single-tau single-temperature NEI model, and a feasible description rests on the two-temperature collisional equilibrium of ionization model we have adopted in our previous analysis of the same data set. We tentatively interpret our results in terms of the superposition of shocks propagating in an inhomogeneous medium, which produces a multitemperature and multiEionization stage plasma. Subject headings: ISM: individual (Vela supernova remnant) E ISM: structure E supernova remnants E X-rays: ISM

Performance of a spherical neutron counter for spectroscopy and dosimetry

A spherical neutron counter for spectroscopy and dosimetry has been developed. The counter consists of a spherical polyethylene moderator and three slender /sup 3/He position-sensitive proportional counters. Rough measurements of neutron fluence spectra and ambient dose equivalents, H*(10), have been done in the moderated-neutron field of JAERI. Characteristics of the counter are examined and compared with those of a Bonner sphere neutron spectrometer.

Structure of the X‐Ray–emitting Gas in the Hydra A Cluster of Galaxies

The temperature and abundance structure in the intracluster medium (ICM) of the Hydra A Cluster of galaxies is studied with ASCA and ROSAT. The effect of the large extended outskirts in the point-spread function of the X-ray telescope on ASCA is included in this analysis. In the X-ray brightness profile, the strong central excess above a single β model, identified in the Einstein and ROSAT data, is also found in the harder energy band (>4 keV). A simultaneous fit of five annular spectra taken with the GIS instrument shows a radial distribution of the temperature and metal abundance. A significant central enhancement in the abundance distribution is found, while the temperature profile suggests that the ICM is approximately isothermal, with a temperature of ~3.5 keV. The ROSAT position-sensitive proportional counter (PSPC) spectrum in the central 15 region indicates a significantly lower temperature than the GIS result. A joint analysis of the GIS and PSPC data reveals that the spectra can be described by a two-temperature model as well as by a cooling flow model. In both cases, the hot-phase gas with a temperature of ~3.5 keV occupies more than 90% of the total emission measure within 15 from the cluster center. The estimated mass of the cooler (0.5-0.7 keV) component is ~(2-6) × 109 M☉, which is comparable to the mass of hot halos seen in non-cD ellipticals. The cooling flow model gives the mass deposition rate of 60 ± 30 M☉ yr-1, an order of magnitude lower than the previous estimation.

The leak microstructure, preliminary results

The Leak Microstructure, a new type of element for position-sensitive proportional gas counter, is introduced. For every single detected ionizing radiation it gives a pair of “induced” charges of the same quantity (pulses of the same amplitude), of opposite sign, with the same collection time and essentially in time coincidence, that are proportional to the collected primary ionization. A gas multiplication up to 1.5 × 10 5 was achieved. The complete absence of insulating materials in the active volume of this microstructure enables to avoid problems of charging-up and makes its behaviour stable and repeatable. By using the charge-pair generated, it allows the development of a position-sensitive detecting board with a two-dimensional read-out. Between the two external surfaces of this board it is possible to insert an intermediate third conducting layer which reduces (or practically suppresses) the capacitive cross-talk between the X and Y read-out strip systems. Furthermore, this intermediate layer can give a very fast trigger to coordinate the charge-pair and to govern the data acquisition system. By reading every strip separately it is possible to resolve the multi hit problem in two-dimensions. Using isobutane as the gas, an energy resolution of about 8% FWHM was recorded with α-particles from an 241Am source. In isobutane gas, X-rays from a 55Fe source and β-particles from a 14C source were also detected.

Evolution in the X‐Ray Cluster Luminosity Function Revisited

We present new X-ray data taken from the ROSAT Position Sensitive Proportional Counter pointing archive for 21 clusters in the Einstein Extended Medium-Sensitivity Survey (EMSS). We have supplemented these data with new optical follow-up observations found in the literature, and, overall, 32 of the original 67 z > 0.14 EMSS clusters now have new information. Using this revised sample, we find no systematic difference, as a function of X-ray flux, between our measured X-ray cluster fluxes and those in the original EMSS (30% scatter). However, we do detect a marginal correlation between this observed difference in the flux and the redshift of the clusters, with the lower redshift systems having a greater scatter by nearly a factor of 2. We have also determined the X-ray extent of these reobserved EMSS clusters and find that 14 of them have significant extents compared with the ROSAT point-spread function. Combining these data with extended clusters seen in the original EMSS sample, at least 40% of z > 0.14 clusters now have an observed X-ray extent, thus justifying their classification as X-ray clusters. Using our improved EMSS sample, we have redetermined the EMSS X-ray cluster luminosity function as a function of redshift. We have removed potential misclassifications and included our new measurements of the clusters' X-ray luminosities and redshifts. We find similar luminosity functions to those originally presented by Henry et al., albeit with two important differences. First, we show that the original low-redshift EMSS luminosity function is insufficiently constrained. Second, the power-law shape of our new determination of the high-redshift EMSS luminosity function (z = 0.3-0.6) has a shallower slope than that seen by Henry et al. We have compared our new EMSS luminosity functions with those recently derived from a nearby sample of X-ray clusters and find that the overall degree of observed luminosity function evolution is mild at best. This is a result of the shallower slope seen in our EMSS high-redshift luminosity function and a more robust low-redshift determination of the X-ray cluster luminosity function from the literature. We have quantified the degree of evolution seen in the X-ray cluster luminosity by using several statistical tests. The most restrictive analysis indicates that our low- and high-redshift EMSS luminosity functions are statistically different at the 95% level. However, other tests indicate that these low- and high-redshift luminosity functions only differ by as little as 1 σ. These data are, therefore, consistent with no evolution in the X-ray cluster luminosity function out to z 0.5.

Development of a high energy X-ray polarimeter for small satellites

We are developing a Thomson-scattering-type polarimeter sensitive in the energy range from 10 keV to 20 keV for a small satellite. The polarimeter consists of three beryllium disks as scatterers and a cylindrical position-sensitive proportional counter as a detector of the scattered X-rays. Its performance has been investigated through computer simulations. From these, it was concluded that the polarimeter can obtain a modulation factor of 34%, a detection efficiency of /spl sim/10%, and a minimum detectable polarization of about 3.0% for Her X-1 in 2 keV bands and a 2/spl times/10/sup 5/ sec observation.