Small Astronomy Satellite 3 - Research Results

Research Results

SAS 3 was especially productive due to its flexibility and rapid responsiveness. Among its most important results were:

• Shortly after the discovery of the first X-ray burster by the ANS, an intense period of burst source discovery by SAS 3 quickly led to the discovery and characterization of about a dozen additional objects, including the famous Rapid Burster, MXB1730-335. These observations established the identification of bursting X-ray sources with neutron star binary systems.

• The RMC was the first instrument to routinely provide X-ray positions that were sufficiently precise to allow followup by optical observatories to establish X-ray/optical counterparts, even in crowded regions near the galactic plane. Roughly 60 positions were obtained with accuracies on the order of 1 arcminute or less. The resulting source identifications helped to connect X-ray astronomy to the main body of stellar astrophysics.

• Discovery of the 3.6 s pulsations of the transient neutron star/Be star binary 4U 0115+63., leading to determination of its orbit and observation of a cyclotron absorption line in its strong magnetic field. Many Be star/neutron star binaries were subsequently discovered as a class of X-ray emitters.

• Discovery of X-ray emission from HZ 43 (an isolated white dwarf), Algol, and from AM Her, the first highly magnetic white dwarf binary system seen in X rays.

• Established the frequent location of X-ray sources near the centers of globular clusters.

• First identification of a QSO through its X-ray emission.

• The soft X-ray instrument established that the 0.10—28 keV diffuse intensity is generally inversely correlated with the neutral H column density, indicating absorption of external diffuse sources by the foreground galactic interstellar medium.

Lead investigators on SAS 3 were MIT professors George W. Clark, Hale V. Bradt, and Walter H. G. Lewin. Other major contributors were Profs Claude Canizares and Saul A. Rappaport, and Drs Jeffrey A. Hoffman, George Ricker, Jeff McClintock, Rodger E. Doxsey, Garrett Jernigan, John Doty, and many others, including numerous graduate students.