Scorpius X-1

Discovery and early study

The possible existence of cosmic soft X-rays was first proposed by Bruno Rossi, MIT professor and board chairman of American Science and Engineering in Cambridge, Massachusetts to Martin Annis, president of AS&E. Following his urging, the company obtained a contract from the United States Air Force to explore the lunar surface prior to the launch of astronauts to the Moon, and incidentally to perhaps see galactic sources of X-rays.

Subsequently, Scorpius X-1 was discovered in 1962 by a team, under Riccardo Giacconi, who launched an Aerobee 150 sounding rocket carrying a highly sensitive soft X-ray detector designed by Frank Paolini. The rocket trajectory was slightly off course but still detected a significant emission of soft X-rays that were not coming from the Moon. Thus fortuitously, and as first pointed out by Frank Paolini, Scorpius X-1 became the first X-ray source discovered outside the Solar System. The angular resolution of the detector did not initially allow the position of Scorpius X-1 to be accurately determined. This led to suggestions that the source might be located near the Galactic Center, but it was eventually realized that it lies in the constellation Scorpius. As the first discovered X-ray source in Scorpius, it received the designation Scorpius X-1.

The Aerobee 150 rocket launched on June 12, 1962 or June 19, 1962, detected the first X-rays from another celestial source (Scorpius X-1) at J1950 RA 16^h 15^m Dec −15.2°. The rocket was designed to observe X-rays from the moon rather than smaller, extrasolar sources, and therefore was unable to accurately retrieve the position and strength of the X-ray signal. The source was estimated to be at J1950 coordinates RA 16^h 15^m Dec −15.2°.

In 1967, before the discovery of pulsars, Iosif Shklovsky examined X-ray and optical observations of Scorpius X-1 and correctly concluded that the radiation comes from a neutron star accreting matter from a companion.