Large-area Proportional Counters Research Articles

Results from AstroSat LAXPC observations of Hercules X-1 (Her X-1)

The Large Area Proportional Counter (LAXPC) instruments onboard the AstroSat Observatory has observed the X-ray binary system Her X-1 during AstroSat observing sessions AO2, AO3 and TO2. These include observations while Her X-1 is in different stages of its 35 day cycle: Low State, Turn-on to Main High State, peak of Main High State and early decline of Main High State. These observations also include a number of dips and one egress of neutron star eclipse. Here we present light curves and softness ratio analysis for these observations and discuss new features of the spectral changes with 35-day phase and orbital phase. We find a new phenomenon for dips during Main High state: About half of the dips show constant softness ratio as count rate decreases, which has not been seen before, and could be caused by highly ionized matter or very dense cold matter. The other half of the dips show the normal decrease of softness ratio as count rate decreases. These are caused by cold matter absorption and were previously known.

Solar wind charge exchange and local hot bubble X‐ray emission with the DXL sounding rocket experiment

AbstractThe Diffuse X‐ray emission from the Local Galaxy (DXL) sounding rocket is a NASA approved mission with a scheduled first launch in December 2012. Its goal is to identify and separate the X‐ray emission of the solar wind charge exchange (SWCX) from that of the local hot bubble (LHB) to improve our understanding of both. To separate the SWCX contribution from the LHB, DXL will use the SWCX signature due to the helium focusing cone at l = 185°, b = –18°. DXL uses large area proportional counters, with an area of 1000 cm2 and grasp of about 10 cm2 sr both in the 1/4 and 3/4 keV bands. Thanks to the large grasp, DXL will achieve in a 5‐minute flight what cannot be achieved by current and future X‐ray satellites (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The scientific objectives of the ASTROSAT mission of ISRO

In this golden age of Space Astronomy high quality data are coming from several spaceborne observatories like Rossi Timing Explorer (RXTE), the Chandra X-ray Observatory, the XMM-Newton, Galex, FUSE and more recently the SUZAKU mission. These missions with capability of high angular resolution, high spectral resolution and large photon throughput are leading to unprecedented advancements in sensitivity for imaging, spectral and timing studies in X-ray and UV bands. These missions have mostly narrow energy band capability in either X-ray or UV regions. There is an urgent need to have a mission with broad spectral band observation capability in X-ray and UV. ASTROSAT is designed to fill this niche area using a variety of experiments covering the 0.3–100 keV band using a combination of an X-ray focusing telescope for soft X-ray imaging, solid state CdZnTe detectors with a coded mask for hard X-ray imaging and spectroscopy and large area proportional counters for high resolution timing studies. Twin UV telescopes operating separately in the near UV (NUV) and far UV (FUV) along with an optical channel provide the highest angular resolution UV imaging over a range of narrow and wide-band filters. The mission also carries an X-ray sky monitor to detect new X-ray transients and monitor known X-ray sources throughout the mission. This complement of scientific instruments, designed and developed by teams in India, Canada and UK, is scheduled for launch in the year 2009. As the first dedicated multiwavelength astronomy mission from India, ASTROSAT is expected to focus on high-resolution UV imaging for morphological studies of galactic and extragalactic objects, broad-band studies of X-ray sources and other multiwavelength targets ranging from nearby stars to the very distant active galactic nuclei. This paper addresses the scientific objectives, description of the instruments to achieve the objectives and the expected science that can emerge from the ASTROSAT mission.

A Bright Transient X-Ray Source Near the Galactic Center Found in Archival Ginga Data from 1987

Abstract A bright transient X-ray source was detected in the direction of the galactic center with Ginga in 1987 March. A sky position was determined from both data obtained with the All Sky Monitor (ASM) and cross-scan data obtained with the Large Area proportional Counters (LAC). Based on the sky position derived from both the ASM and the LAC data, this source was designated as GS 1741$-$288. At the beginning of the Ginga observations, GS 1741$-$288 was in the active state: its energy flux in the 2–10 keV energy band was $\sim$10$^{-8}$ergs$^{-1}$cm$^{-2}$. The ASM light curve showed that the intensity gradually decayed with an e-folding time of $190\pm9$d. No remarkable feature, such as periodic or quasi-periodic oscillations was found. The spectral and temporal properties suggest that GS 1741$-$288 is likely to be a low-mass X-ray binary system containing a weakly magnetized neutron star. Possible identification of the source is also discussed.

Efficiency calibration and determination of performance characteristics of a large area proportional counter for the field measurement of 238Pu in soils

A large area proportional counter (LAPC) X-ray detector and a method for calibrating the detector system for 238Pu contamination in soils has been developed. The system utilizes the LAPC to measure the L X-ray triplet emitted in the decay of 238Pu at energies of 13.6, 17.13, and 20.29 keV. The LAPC has dimensions of 16.5’70.5’5.9 cm3 (L’W’H) and is filled with a mixture of 90% xenon and 10% methane at a pressure of 0.15 MPa. The detector has a thin (0.025 cm) beryllium window and aluminum support grid with an effective area of 850 cm2. The detector was calibrated for efficiency via semi-empirical methodology consisting of measurements with International Atomic Energy Agency and National Institute of Standards and Technology (NIST) traceable sources combined with fluence rate calculations using Monte Carlo and point-kernel modeling scenarios. The detector efficiency was then empirically measured using NIST traceable soil standards, and the results were compared with the semi-empirical modeled value. Operational performance characteristics including detector field of view, lower limit of detection, and energy resolution of the system were also determined through a series of controlled measurements. The LAPC and associated electronics are mounted on a pushcart with a computer and global positioning system to allow for real-time surveying and mapping of potentially contaminated land areas and detecting 238Pu contamination at concentrations of 1.9 Bq/g of soil. The system, measurement methods, and results are presented and discussed.

Measuring the power spectrum of density fluctuations at intermediate redshift with X-ray background observations

The precision of intensity measurements of the extragalactic X-ray Background (XRB) on an angular scale of about a degree is dominated by spatial fluctuations caused by source confusion noise. X-ray source counts at the flux level responsible for these fluctuations will soon be accurately measured by new missions and it will then be possible to detect the weaker fluctuations caused by the clustering of the fainter, more distant sources which produce the bulk of the XRB. We show here that measurements of these excess fluctuations at the level of 0.2 per cent are within reach, improving by an order of magnitude on present upper limits. Together with the redshift evolution of the X-ray volume emissivity in the Universe, this can be used to measure the power spectrum of the density fluctuations at comoving wavevectors 0.01-0.1 h/Mpc at z=1-2 with a sensitivity better than the predictions from large-scale structure models. A relatively simple X-ray experiment, carried out by a large-area proportional counter with a 0.5-2 deg^2 collimated field-of-view scanning the whole sky a few times, would be able to determine the power spectrum of the density fluctuations near its expected peak in wavevector with an accuracy better than 10 per cent.

Background reduction in a balloon-borne hard X-ray telescope

We have been carrying out a series of balloon flight experiments using a large area proportional counter based (xenon filled) hard X-ray telescope and have studied in detail the spectral and temporal characteristics of several cosmic hard X-ray sources. The detector system uses multi-cell multi-layer configuration and for background reduction passive shielding, active anti-coincidence on three sides of the detector and mutual anti-coincidence for the active cells are employed. Further, K-gating technique is used to improve the energy resolution and detection efficiency. We present the effectiveness of the various background rejection techniques using a Monte-Carlo simulation and critically evaluate the possible improvements in the background rejection.

Hard X‐Ray Emission from the Galactic Ridge

Hard X-ray and γ-ray emissions from the Galactic ridge were studied with the large area proportional counter (LAC) on the Ginga satellite and a balloon-borne detector Welcome-1. In the scanning observations with the LAC, diffuse hard X-rays were detected along the Galactic plane between l = -20° and l = 40°. The measured spectrum shows that a hard component exists in the Galactic ridge emission above 10 keV, in addition to the hot plasma component. The estimated luminosity of the Galactic ridge emission is around 2 × 1038 ergs s-1 in the 3-16 keV band. Welcome-1 observed the γ-ray ridge emission at around l ~ 345° between 50 and 600 keV. These two results and a recent COMPTEL study suggest that the spectrum of the diffuse Galactic ridge emission extends over the keV-MeV range. From the observed spectral slope, bremsstrahlung by electrons is shown to be the dominant emission mechanism. This implies that low-energy electrons must be supplied continuously to sustain emission in the hard X-ray band. We propose a scenario in which the thermal electrons in the hot plasma responsible for the strong Fe K X-ray emission are shock-accelerated continuously in supernova remnants (SNRs), producing the observed hard X-ray and γ-ray emissions from the Galactic ridge.

The Ionic Charge of Solar Energetic Particles with Energies of 0.3–70 MeV per Nucleon

With the three particle sensors Low Energy Ion Composition Analyzer (LICA), Heavy Ion Large Area Proportional Counter Telescope (HILT), and Mass Spectrometer Telescope (MAST) on board the polar orbiting Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite, the ionic charge of solar energetic particles (SEP) was measured over a wide energy range from 0.3 to 70 MeV per nucleon. For each sensor, the evaluation was performed separately. The results obtained with LICA (0.3-10 MeV per nucleon) and MAST (15-70 MeV per nucleon) were published earlier by Mason et al. and Leske et al., respectively. In this work we present the results of the HILT sensor (7-50 MeV per nucleon) and discuss the combined results of the three instruments. With HILT, the mean ionic charge of SEP was measured for carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, argon, calcium, and iron in the energy range 7E50 MeV per nucleon during two consecutive large SEP events in 1992 OctoberENovember. The mean ionic charge was inferred from the rigidity-dependent geomagnetic flux cutoff. The coronal temperatures deduced from the mean ionic charges are well in accordance with the value of ~2x10^6 K except for neon and magnesium, as previously reported. The data measured with the three sensors, LICA, HILT, and MAST, agree well and are in accordance with data previously measured at energies below 3 MeV per nucleon (Luhn et al.), except for iron, where we observed a significant energy dependence of the mean charge over the energy range 0.3-70 MeV per nucleon.

Prospects for Coordinated Observations with XTE

AbstractThe X-ray Timing Explorer (XTE) is a NASA satellite designed to perform high-time-resolution studies of known X-ray sources. The two main experiments are a large-area proportional counter array (PCA) from the Goddard Space Flight Center (GSFC) and a high-energy X-ray timing experiment (HEXTE) from the University of California at San Diego (UCSD). The PCA data is processed by an electronic data system (EDS) built by the Massachusetts Institute of Technology (MIT) that performs many parallel processing analysis functions for on-board evaluation and data compression. MIT also provide an all-sky monitor (ASM) experiment so that XTE can be slewed rapidly to new transient sources. The spacecraft provides a mean science telemetry rate for the PCA of ~20 kilobits per second (kbps), with bursts to 256 kbps for durations of 30 minutes. Photons are tagged to 1 μs and absolute timing should be better than 100 μs. XTE is due for launch in late August 1995 and the first NASA Research Announcement (NRA) is due out in January 1995. This paper summarises XTE’s performance and then discusses the interactive and flexible operations of the satellite and some of the science it can do. These features should make XTE a productive spacecraft for coordinated observation programs.

Spectral evolution during pre-eclipse dips in Hercules X-1

view Abstract Citations (18) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral Evolution during Pre-Eclipse Dips in Hercules X-1 Leahy, D. A. ; Yoshida, A. ; Matsuoka, M. Abstract Hercules X-1 was observed by the Large Area Proportional Counter (LAC) instrument on the Ginga satellite during 1988 August when pre-eclipse dips of Her X-1 were taking place. A detailed analysis of the X-ray spectra during the dips is presented here. The dips are confirmed to be caused by absorption, and for the first time the evolution of absorption during a dip is determined. However, in addition to the absorbed component, there is a significant unabsorbed continuum component from an extended corona around the neutron star, which also changes with time. By analyzing the spectral changes, evidence is found for important properties that have not been previously detected in X-ray binaries: the power-law index spectrum increases with luminosity; the covering fraction of a scattering corona by the accretion disk is variable on several minute timescales; and the flourescent iron line energy is downshifted by Compton scattering. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174732 Bibcode: 1994ApJ...434..341L Keywords: Absorption Spectra; Eclipses; Eclipsing Binary Stars; Evolution (Development); Spectrum Analysis; X Ray Absorption; X Ray Binaries; X Ray Spectra; Accretion Disks; Compton Effect; Continuous Spectra; Ginga Satellite; Iron; Satellite-Borne Instruments; Spectral Energy Distribution; Stellar Coronas; Stellar Luminosity; Astronomy; STARS: INDIVIDUAL CONSTELLATION NAME: HERCULES X-1; X-RAYS: STARS full text sources ADS | data products SIMBAD (2)

High speed data acquisition system for large area proportional counters

A modular, UNIX/X-Windows/Sun SPARC-based data acquisition and analysis system provides NASA X-Ray Timing Explorer (XTE) Proportional Counter Array (PCA) scientists with near real-time access to space flight instrument ground test data. This system processes data directly from five large-area, xenon-filled low-background collimated proportional counters at rates up to 2 MB/s in a networked, real-time environment. Science events are sent serially from the proportional counter flight electronics and multiplexed on a custom-designed data acquisition board. Each event is tagged with a time stamp of 1 /spl mu/s resolution and a detector identifier. A commercial Direct Memory Access (DMA) board interfaces directly to the data acquisition board allowing asynchronous transfer of buffered data to software residing on a high performance workstation. A windows-based interface provides an operator with acquisition command and control functions to capture data through the DMA board. Data is collected, buffered, and archived to magnetic disk. Histogramming and statistical functions are provided by the software enabling real-time pulse height spectroscopy, rate analysis, and spectral analysis. >

Ginga observations of the X-ray spectra of Seyfert galaxies

We present an analysis of 60 spectra of 27 Seyfert galaxies observed with the Ginga Large Area proportional Counter (LAC). The 2–10 keV continuum is found to be compatible with previous spectral surveys, but a spectral flattening, or ‘hard tail’, is evident above 10 keV. Excess absorption over the Galactic column density is found in around half of the sources, with an equivalent hydrogen column density |$N_{\rm H}=10^{21-22} \ {\rm {cm}}^{-2}$|⁠, Spectral features are found to be common, with all but two of the sources showing evidence for an iron |${\rm K}\alpha$| emission line. The mean energy of the line, at around 6.4 keV, indicates an origin via fluorescence in near-neutral material. The mean equivalent width (100–150 eV) is large, considering that the sources are relatively unobscured. At least |$\sim 40$| per cent of the sources show an additional improvement when an absorption edge is added, with an energy indicating an origin in highly ionized iron and equivalent hydrogen column density |$N_{\rm {HFe}}$| of order |$10^{23} \ {\rm {cm}}^{-2}$|⁠, These observations strongly imply the existence of two gas components – optically thick material and strongly photoionized gas of lower column density in the line of sight. The first is responsible for the bulk of the emission line, and Compton down-scattering and absorption result in a ‘reflected’ continuum component which produces the hard tail. The mean line and reflected continuum properties are in excellent agreement with those expected in a flattened geometry. Although other cold matter distributions are not ruled out, an origin in an accretion disc around the putative black hole seems most likely. The second component is highly ionized gas, the so-called ‘warm absorber’, which is responsible for the observed iron edge at 8–9 keV and complex absorption at soft X-ray energies. This plasma is difficult to detect at other wavelengths, and may form an outflow or wind. Both the reflection component and the warm absorber considerably modify the spectrum in the X-ray band, and previous observations with lower signal-to-noise ratio have resulted in misleading estimates of the spectrum of the underlying continuum. Rather than the |$\Gamma=1.7$| indicated by HEAO-1 and EXOSAT, we find that the mean X-ray continuum is best modelled by a power law with photon index in the range |$\Gamma=1.9-2.0$|⁠. These observations have considerable implications for the power-production mechanism in active galactic nuclei (AGN), and provide important diagnostics of the accretion flow and environment around the central black hole.

Characterization of large-area reference sources for the calibration of alpha-contamination monitors

A simple method has been developed whereby the activity of a large-area reference source for the calibration of alpha-contamination monitors can be determined from the measured alpha-particle flux. A correction factor k is determined from the pulse height spectrum of the source in a large-area proportional counter to take into account backscattering and self-absorption in the source. This correction factor is used to calculate the activity with an uncertainty not exceeding 10%.

Periodic components in Cyg X-3

Hard X-ray observations of Cyg X-3 in the energy range 20–100 keV were made with a Balloon-borne telescope using two large area proportional counters. The source was seen with a total significance of 20α.A 121 s periodicity was seen during Fourier analysis of the data. The phenomenon can be interpreted as due to transient pulsation since no other peak was seen in our data. Quasi-periodic oscillation in the range 0.06–20 mHz have been observed from Cyg X-3 at lower energies. Interestingly, most of the reported periods are multiple of the present measurements. The observed pulsation at high energies indicate the occasional unstable behaviour of the inner parts of the accretion disk connected with the basic rotation period of the compact object.The 4.8h modulation, characteristic of the orbital period of the binary system was seen in the data, with a broad maximum between the phase 0.3 to 0.7.

HILT: a heavy ion large area proportional counter telescope for solar and anomalous cosmic rays

The HILT sensor has been designed to measure heavy ion elemental abundances, energy spectra, and direction of incidence in the mass range from helium to iron and in the energy range 4-250 MeV/nucleon. With its large geometric factor of 60 cm/sup 2/ sr the sensor is optimized to provide compositional and spectral measurements for low-intensity cosmic rays, i.e., for small solar energetic particle events and for the anomalous component of cosmic rays. The instrument combines a large-area ion-drift-chamber-proportional-counter system with two arrays of 16 Li-drifted solid state detectors and 16 CsI crystals. The multi-dE/dx-E technique provides a low-background mass and energy determination. The sensor also measures particle direction. By combining these measurements with the information on the spacecraft position and attitude in the low-altitude polar orbit, it will be possible to infer the ionic charge of the ions from the local cutoff of the Earth's magnetic field. The ionic charge in this energy range is of particular interest because it provides unique clues to the origin of these particles and has not been investigated systematically so far.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cyclotron line features in the spectrum of the transient X-ray pulsar X0115 + 634

An outburst of the transient X-ray pulsar X0115 + 634 was detected with the All Sky Monitor (ASM) on board Ginga on February 5, 1990. Follow-up observations with the large-area proportional counters (LACs) revealed complex changes in the energy spectrum which depend on the phase of the 3.6 s pulsation. Characteristic structures in the spectra above 10 keV can be best interpreted as two dips at about 12 and about 23 keV, although not at all phases. The results strongly suggest that the structures in the spectra are due to cyclotron resonant scattering and the two apparent absorption lines are ascribed to the fundamental and second harmonics. This indicates a magnetic field strength on the neutron star surface of about 1 {times} 10 to the 12th G. Equivalent widths of the second harmonic line are about 2 times larger than those of the first harmonic line, depending on the pulse phase. 25 refs.

X-ray continuum and evidence for an iron emission line from the quasar E1821 + 643

This paper reports on the 2-10 keV spectrum of the quasar E1821 + 643, obtained with the large-area proportional counters aboard the Ginga spacecraft on two occasions: May 12-14, 1987 and September 27, 1988. The spectrum shows strong evidence for the presence of a redshifted iron K emission line of a 5.1 + or - 0.2 keV energy, and an observed equivalent width of 210 + or - 80 eV. The E1821 + 643 appeared to be embedded within a cluster of galaxies which could contribute part of the observed line. A possibility is suggested that iron emission lines may be a common feature in X-ray spectra of quasars. 41 refs.

X-Ray Astronomy Satellite Ginga

AbstractThe X-ray astronomy satellite Ginga carries three scientific instruments, the Large Area proportional Counters (LAC), All Sky X-ray Monitor (ASM) and Gamma-ray Burst Detector (GBD). The LAC is the main instrument with an effective area of 4000 cm2 giving it the highest sensitivity to hard X-rays so far achieved. Ginga observed about 250 targets up to the end of 1989.

Studies on the Detection of Surface Contamination by Electron Capture Emitters

Contamination in German nuclear power plants often contains the nuclides 51Cr, 54Mn, 55Fe, 58Co and 65Zn. These nuclides decay principally by electron capture and contamination containing these nuclides is not easy to detect. It will be shown that with the large-area proportional counters generally used for contamination detection it is possible to detect surface contamination of less than 5 Bq.cm-2 generated by electron capture emitters if argon-methane is used as the counter gas. Contaminations of even less than 0.5 Bq.cm-2 can be detected by using suitable pulse height discrimination.