X-ray Imaging Telescope Research Articles

The X-ray imaging telescopes on Exosat

The instrument configuration and performance characteristics of the X-ray imaging telescopes on EXOSAT are described. The instrument comprises two fully independent Wolter I imaging telescopes. Each telescope can be used in either of two principal modes: (i) an imaging mode with either a position sensitive proportional counter or a channel multiplier array plate in the focal plane, (ii) a spectrometer mode which features a 500 lines/mm and/or a 1000 lines/mm transmission grating as dispersive element.

The Rosat mission

The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 105) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets. The X-ray telescope consists of a fourfold nested Wolter type I mirror system with 80 cm aperture and 240 cm focal length, and three focal plane detectors. In the baseline version these will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 20 × 20.

A Position Sensitive Gas Scintillation Proportional Counter for X-Ray Astronomy

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.

Lobster eyes as X-ray telescopes

view Abstract Citations (123) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lobster eyes as X-ray telescopes. Angel, J. R. P. Abstract A new optical configuration for grazing-incidence, imaging X-ray telescopes is described that is similar to the reflective eyes of macruran crustaceans such as lobsters. The field of view can be made as large as desired, and it is practical to achieve good efficiency for photon energies up to 10 keV. Spatial resolution of a few seconds of arc over the full field is possible, in principle, if very small reflecting cells can be fabricated. Two model telescopes are described. The first has a field similar to that of optical Schmidt telescopes (8 deg), an aperture of 2.5 m, and a spatial resolution of 30 arcsec. In a two-year mission it would survey the entire sky to the limiting sensitivity of the Einstein telescope, and it has the advantage of good response at the 7 kV iron emission lines. The second telescope, an all-sky monitor with a 2-pi ster field of view, is a hemisphere 3 m in diameter. It reaches the limiting sensitivity of Uhuru in approximately one hour with positions accurate to approximately 2 arcmin, and can detect and locate quite faint burst sources. Publication: The Astrophysical Journal Pub Date: October 1979 DOI: 10.1086/157397 Bibcode: 1979ApJ...233..364A Keywords: Grazing Incidence; Grazing Incidence Telescopes; Optical Properties; X Ray Telescopes; Arthropods; Eye (Anatomy); Fabrication; Mirrors; Nickel; Resolution; Visual Fields; Astronomy; X-Ray Telescopes full text sources ADS |

Soft X-ray structure of the Coma cluster of galaxies

view Abstract Citations (31) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Soft X-ray structure of the Coma cluster of galaxies. Gorenstein, P. ; Fabricant, D. ; Topka, K. ; Harnden, F. R., Jr. Abstract Results are reported for an observation of the Coma cluster with an imaging X-ray telescope system aboard a sounding rocket. A two-dimensional X-ray map of the cluster in the energy range from 0.15 to 2.0 keV is presented. The radial distribution, granularity, and ellipticity of the X-ray surface brightness are investigated, and the spectrum and flux within the field of view are analyzed. These properties are then examined quantitatively by comparing the observations with models through the use of a chi-squared test. It is found that: (1) no single galaxy contributes more than a few percent of the total X-ray flux of the Coma cluster; (2) the X-ray source is diffuse but granular on a scale of several arcmin, particularly in the central region; (3) the centroid of the X-ray source is at a local intensity minimum; and (4) the data are most consistent with an isothermal hydrostatic model. Publication: The Astrophysical Journal Pub Date: May 1979 DOI: 10.1086/157058 Bibcode: 1979ApJ...230...26G Keywords: Astronomical Maps; Galactic Clusters; Galactic Radiation; X Ray Astronomy; Galactic Structure; Spatial Distribution; Spectrum Analysis; X Ray Sources; Astrophysics; Clusters of Galaxies:Coma; Clusters of Galaxies:Models; Clusters of Galaxies:X Rays full text sources ADS |

Detection of soft X-rays from Alpha Lyrae and Eta Bootis with an imaging X-ray telescope

Results are presented for observations of Alpha Lyr (Vega) and Eta Boo with an imaging X-ray telescope during two rocket flights. It is found that Vega and Eta Boo are soft X-ray sources with respective luminosities of approximately 3 x 10 to the 28th erg/s (0.15-0.8 keV) and 1 x 10 to the 29th erg/s (0.15-1.5 keV). Surface X-ray luminosities of about 640,000 erg/sq cm per sec for Vega and 300,000 erg/sq cm per sec for Eta Boo are estimated and shown to fall within the range of solar coronal X-ray emission. It is concluded that in view of the substantially larger surface areas of these stars, the relatively large total soft X-ray luminosity (as compared with that of the sun) can in both cases be understood as resulting from a moderately active corona, although the Vega observation is in severe conflict with simple models for X-ray emission from single main-sequence stars.

X-ray images of Puppis A and IC 443

X-ray images of the Puppis A and IC 443 supernova remnants, recorded with a rocket-borne imaging X-ray telescope, are presented. These images indicate a complex X-ray morphology and only weak correlation with the radio and optical pictures. The observations lend further support to a picture wherein Puppis A, IC 443, and possibly most other supernova remnants of moderate age result from blast waves propagating into a substantially inhomogeneous interstellar medium. We conclude that caution must be used in interpreting X-ray observations in terms of simple blast-wave models where spherical symmetry is assumed.

X-ray image of the Cygnus Loop

An X-ray picture of the Cygnus Loop, recorded with an imaging X-ray telescope, is presented. The results are highly suggestive of a limb-brightened shell of hot gas which results from the expansion of a blast wave into the interstellar medium. Spatial structure is clearly evident on scale sizes down to about 1/4 deg, a likely indication of the inhomogeneities in the interstellar medium. No evidence is found for any discrete X-ray-emitting remnant of the original supernova explosion.

X-Ray Observations of Clusters of Galaxies

X-ray astronomy has, in the past year, seen the publication of the second Ariel (2A) and fourth Uhuru (4U) catalogues of X-ray sources. A number of new X-ray cluster identifications and the confirmation of several others has resulted. in this review I will briefly summarise the situation regarding identifications and, for the 2A clusters, discuss the luminosity function and the possible relationships between a number of cluster X-ray and optical properties. Superclusters have been tentatively proposed as a class of X-ray sources and I will comment briefly on recent observations of these objects. Cluster structure has been studied by the Copernicus and SAS-3 spacecraft and by a number of rocket observations with imaging X-ray telescopes undertaken by the Harvard Centre for Astrophysics. I will review the current situation regarding structural measurements. Finally I will discuss the present status of Iron line observations at 6.7 keV in cluster spectra and the estimates of Fe abundance that result from these data.

Structure of the X-ray source in the Virgo cluster of galaxies

view Abstract Citations (66) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Structure of the X-ray source in the Virgo cluster of galaxies. Gorenstein, P. ; Fabricant, D. ; Topka, K. ; Tucker, W. ; Harnden, F. R., Jr. Abstract High-angular-resolution observations in the 0.15-1.5-keV band with an imaging X-ray telescope shows the extended X-ray source in the Virgo cluster of galaxies to be a diffuse halo of about 15 arcmin core radius surrounding M87. The angular structure of the surface brightness is marginally consistent with either of two simple models: (1) an isothermal (or adiabatic or hydrostatic) sphere plus a point source at M87 accounting for 12% of the total 0.5-1.5-keV intensity or (2) a power-law function without a discrete point source. No evidence for a point source is seen in the 0.15-0.28-keV band, which is consistent with self-absorption by about 10 to the 21st power per sq cm of matter having a cosmic abundance. The power-law models are motivated by the idea that radiation losses regulate the accretion of matter onto M87 and can account for the observed difference in the size of the X-ray source as seen in the present measurements and at higher energies. Publication: The Astrophysical Journal Pub Date: September 1977 DOI: 10.1086/182519 Bibcode: 1977ApJ...216L..95G Keywords: Astronomical Models; Galactic Clusters; Galactic Structure; X Ray Sources; Angular Resolution; Brightness; Emission Spectra; Point Sources; Radiant Flux Density; Spaceborne Astronomy; Astrophysics full text sources ADS | data products NED (1)

Simultaneous optical and x-ray imaging telescopes

Simultaneous optical and x-ray imaging telescopes

A soft X-ray image of the Algol region

Algol (Beta Persei) has been detected in two separate exposures of an imaging X-ray telescope. The 0.15- to 2-keV X-ray luminosity is approximately 2 by 10 to the 30th power erg/s. The X-ray flux is interpreted as thermal emission produced by direct accretion of mass from the K star to the B8 member of the triple star system.

Negative Affinity X-Ray Photocathodes

True image-forming telescopes for use in X-ray astronomy are available now with arc-second resolution for A ≥3A. Such telescopes have been very successfully applied on rockets and on the recent Skylab mission for solar observations. However, their application to observations of extra-solar X-ray sources has been severely limited due to a lack of sensitive X-ray imaging detectors. We describe here a new type of detector using a GaAs photocathode with quantum efficiency approaching 100%. This detector allows us to detect sources 10 to 20 times fainter than previously possible, while preserving spatial resolution on the several micron scale. We present data on the X-ray photoelectron yield for GaAs (Cs-O2) negative affinity cathodes both in reflection mode using a thick cathode and in the transmission mode using a 3.7 micron wafer. A theoretical model is developed and compared with the data to determine the electron diffusion length, the front surface electron reflection coefficient and the back surface electron escape probability for the transmission cathode. There is good agreement between the crystal parameters obtained from X-ray data and from optical data. Application to X-ray telescope imaging in a practical device is discussed.