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X-Ray Scanning Modulation Collimator (A-3)

NSSDCA ID: 1977-075A-03

Mission Name: HEAO 1
Principal Investigators:Dr. Daniel A. Schwartz
Principal Investigators:Dr. Hale V. Bradt


This experiment used a scanning modulation collimator (SMC) instrument to determine, for selected X-ray sources, their position within 5 arc-s and their angular size to a precision of 5-10 arc-s in three energy intervals from 1 to 15 keV, and to study the structure of their X-ray emission to a precision of 10 arc-s in three energy intervals from 1 to 15 keV. The SMC was composed of two parts, each containing four wire grid planes. Each provided a location and angular size measurement in one dimension. An additional collimator located forward to the front grid restricted the overall instantaneous field of view to 4-deg x 4-deg FWHM for each SMC. The outward view direction was perpendicular to the spacecraft spin axis (Z axis) and, hence, the instrument scanned a great circle band on the sky. The two parts of the SMC differed by having their plane of maximum transmission inclined +10 deg and -10 deg to the scan direction. Precise two-dimensional locations were determined by the intersections of the locations obtained from each of the collimators. The angular response of the two SMC components was 30 and 120 arc-s, which extended the dynamic range up to 16 arc-min, over which angular size and structure measurements were made. The SMC instrument was capable of detecting X-ray sources with an intensity of 1E-3 that of the Crab Nebula. This experiment was also equipped with two aspect sensors to provide data on the stellar orientation of the collimator axes to achieve the 5-arc-s position of sources. For more details, see R. E. Griffiths et al., Astrophy. J., v. 230, p. L21, 1979.

Alternate Names

  • HEAO1/X-RayScanningModulationCollimator_A-3_
  • Scanning Modulation Collimator

Funding Agency

  • NASA-Office of Space Science (United States)


  • Astronomy: X-Ray

Additional Information

Questions and comments about this experiment can be directed to: Dr. Cynthia Y. Cheung



NameRoleOriginal AffiliationE-mail
Dr. Hale V. BradtPrincipal InvestigatorMassachusetts Institute of
Dr. Daniel A. SchwartzPrincipal InvestigatorSmithsonian Astrophysical
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