one or two byte time tag, allowing precision timing of objects such as gamma-ray bursts and pulsars. Results of the experiment included a catalog of the positions and intensities of hard X-ray (10–200 keV) sources, a strong observational basis for extremely strong magnetic fields (of order 1013 G) on the rotating neutron stars associated with Her X-1 and 4U 0115+634, a definitive diffuse component spectrum between 13 and 200 keV, discovery of the power-law shape of the Cygnus X-1 power density spectrum, and discovery of slow intensity cycles in the X-Ray sources SMC X-1 and LMC X-4, resulting in approximately 15 Ph.D theses and ~100 scientific publications. The A4 instrument was provided and managed by the University of California at San Diego, under the direction of Prof. Laurence E. Peterson, in collaboration with the X-ray group at MIT, where the initial A4 data reduction was performed under the direction of Prof. Walter H. G. Lewin. See also Einstein Observatory (HEAO 2) HEAO Program High Energy Astronomy Observatory 3 Timeline of artificial satellites and space probes References External links 1st High Energy Astrophysics Observatory (HEAO 1. GSFC. NASA ) on the internet The Star Splitters by Wallace H. Tucker, 1984 Space telescopes X-ray telescopes Gamma-ray telescopes 1977 in spaceflight August 1977 events in the United States Spacecraft launched in 1977