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Cosmic X-Ray Sources in the Range 1.5 to 9 A

NSSDCA ID: 1971-083A-04

Mission Name: OSO 7
Principal Investigator:Dr. George W. Clark


The purpose of this MIT experiment was to survey the entire sky for cosmic X-ray sources in the energy range 1 to 60 keV with an angular resolution of about 1 deg and perform spectral analysis in five broad bands. Each portion of the sky was viewed several times during each year of operation. Two multicompartmented proportional counters equipped with honeycomb collimators (3.5-sq deg solid angle) were mounted in one segment of the OSO wheel section, with the centers of their fields of view oriented 15 deg above and 15 deg below the spacecraft equator. X-rays were detected in one or another of four compartments depending upon their energy. Low-energy photons were stopped in the first compartment, higher-energy photons penetrated to the second compartment, and photons of even higher energies penetrated through the first and second compartments to the third and fourth compartments. The energy bands were logarithmically equispaced. A separate single compartment counter with a thin aluminum window detected photons between 1.0 and 1.5 keV. Counts from each compartment were stored in one of 256 accumulators corresponding to a division of the spacecraft spin into 256 sectors. Inflight calibration was provided by periodic exposure to a radioactive source. For more details, see G. W. Clark et al., Ap. J., v. 179, p. 263, 1973.

Alternate Names

  • Multicolor Survey of the Positions and Time Variations of Cosmic X-Ray Sources
  • OSO7/CosmicX-RaySourcesintheRange1_5to9A


  • Astronomy: X-Ray

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. Hale V. BradtOther InvestigatorMassachusetts Institute of
Dr. Walter H. G. LewinOther InvestigatorMassachusetts Institute of
Dr. Herbert W. SchnopperOther InvestigatorDanish Space Research Institute
Dr. George W. ClarkPrincipal InvestigatorMassachusetts Institute of
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