The HEAO-1 Satellite

Credit: NASA

Beginning in 1977, NASA launched a series of very large scientific payloads called High Energy Astronomy Observatories (HEAO). The first of these missions, HEAO-1 surveyed the X-ray sky almost three times over the 0.2 keV - 10 MeV energy band, provided nearly constant monitoring of X-ray sources near the ecliptic poles. More detailed studies of a number of objects were made through pointed observations lasting typically 3-6 hours.

Mission Characteristics

• A1 - Large Area Sky Survey experiment (LASS) :
  0.25-25 keV, eff. area 7 modules each of 1350 - 1900 cm², FOV varied between 1° X 4° to 1° x 0.5° for finest collimators.
• A2 - Cosmic X-ray Experiment (CXE) :
  six separate proportional counters
  • Low Energy Detectors (LED) 0.15-3.0 keV, eff. area 2 detectors of 400 cm² each
  • Medium Energy Detector (MED) 1.5-20 keV, eff. area 1 detector at 800 cm²
  • High Energy Detector (HED) 2.5-60 keV, eff. area 3 detectors at 800 cm² each
  MED and HEDs had various FOV settings, 1.5° x 3°, 3° x 3° and 3° x 6°
• A3 - Modulation Collimator (MC) :
  0.9-13.3 keV, eff. area 2 collimators 400 cm² (MC1) & 300 cm² (MC2), FOV 4° X 4°
• A4 - Hard X-Ray / Low Energy Gamma Ray Experiment :
  seven inorganic phoswich scintillator detectors
  • Low Energy Detectors 15-200 keV, eff. area 2 detectors 100 cm² each, FOV 1.7° x 20°
  • Medium Energy Detectors 80 keV - 2 MeV, eff. area 4 detectors 45 cm² each, FOV 17°
  • High Energy Detector 120 keV - 10 MeV, eff. area 1 detector 100 cm², FOV 37°

• Complete flux-limited High Galactic Latitude Survey (Piccinotti et al. 1982).
• Measurement of X-ray background from 3-50 keV (Marshall et al. 1980, ApJ, 235, 4.)
• Comprehensive catalog of X-ray sources (one for each experiment).
• Several hundred optical companions and source classifications based on X-ray source positions.
• Monitored variability of a variety of objects from AGNs to X-ray binaries.
• Studied aperiodic variability in Cyg X-1 on timescales on a few milliseconds
• Discovered the first eclipse seen in a low-mass X-ray binary.