Multiwavelength Astronomy

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X-ray Science, George Clark

The Discovery of Cosmic X-rays

Rossi' strategy for investigating an unexplored aspect of nature was to cast as wide a net as possible in hopes of catching something interesting. In 1959 it occurred to him that the instruments used so far in X-ray astronomy, in particular by Herbert Friedman and his group at the Naval Research Laboratory (NRL) in their pioneering investigations of solar X-rays, were too small in area and field of view to have caught any much fainter extrasolar source if any existed, even if they had been used in a broad sky survey. The Sun was the only known source of cosmic X-rays, but at the distance of the nearest star it would be 60 billion times fainter. Nevertheless, Rossi thought that casting a wider net might catch something unexpected.

At that time, the M.I.T. Cosmic Ray Group was completely occupied with air showers, particle physics, gamma rays, and a recent Rossi initiative concerned with measurements of the interplanetary plasma. So Rossi brought his idea to Martin Annis, president of American Science and Engineering, Inc., a small research and development company in Cambridge.

AS&E began in the fall of 1957 when Annis, a friend of mine from graduate school and a former student of Rossi's, invited me to join in founding a company that would be called American Science and Engineering, Inc. Though not involved in the founding of AS&E, Professor Rossi accepted Annis’s invitation to be Chairman of the Board of Directors and Chief Scientific Consultant.

Annis responded enthusiastically to Rossi’s idea, and suggested he discuss it with Riccardo Giacconi, whom he had recently hired to set up a space science division that could respond to opportunities for defense contracts involving measurements of X-rays from bomb tests at high altitudes. Giacconi had extensive experience in cosmic ray research at the Universities of Milan, Indiana and Princeton. The discussion took place during a party at the Rossi's home in September of 1959. Giacconi seized the idea, and pursued it vigorously in parallel with his other responsibilities. That fall I worked with Giacconi and Rossi on an internal AS&E report on the current state of theoretical and experimental X-ray astronomy. It was a basis for two proposals to NASA, one for support of the development of image forming grazing-incidence reflection X-ray optics, and the other for exploratory rocket experiments. NASA accepted the former and rejected the latter.

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This material is based upon work supported by NASA under Grant Nos. NNX09AD33G and NNX10AE80G issued through the SMD ROSES 2009 Program.

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