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Frederick D. Seward is an X-ray astronomer at the Smithsonian Astrophysical Observatory. He was one of the pioneers of X-ray astronomy, leading the Lawrence Livermore National Laboratory rocket program in the 1960s, and is an expert on X-ray studies of supernova remnants.

Early life and education
Frederick Downing Seward was born in 1931. He is the great-great-grandson of Edwin Polydore Seward, brother of William_H._Seward. Seward received a Bachelor of Science degree in physics from Princeton University in 1953. He went on to do a PhD in experimental nuclear physics at the University of Rochester which he completed in 1958.

Career
After his PhD, Seward joined the Lawrence Livermore National Laboratory to work on linear accelerator experiments but in 1960 shifted his interests from nuclear physics to astronomy and space research. As part of the Livermore group, he flew auroral X-ray radiation experiments on the Agena aft rack of several CORONA spy satellites including Discoverer 29 and Discoverer 31. Seward discovered the existence of the South Atlantic Anomaly with these data, although the result was not published at the time. Seward then participated in the 1962 atmospheric nuclear test series in the Pacific, Operation Dominic, and with Jim Carruthers launched Nike-Apache sounding rockets from Johnston Island and Kauai to measure the radiation flux from the Starfish Prime high altitude nuclear explosion in July 1962.



After the Partial Nuclear Test Ban Treaty, the Livermore team became the readiness group, tasked with maintaining the nation's ability to perform nuclear tests should the treaty lapse. The rockets and X-ray detectors used to measure the flux of artificial nuclear explosions were repurposed to study cosmic X-rays. Seward led a research program to study extrasolar X-ray sources using sounding rockets provided by the Sandia National Laboratories, and pioneered the use of sounding rockets launched from flotation rafts in the ocean in order to study the South Atlantic Anomaly. Seward showed that the X-ray emission from the binary source Sco X-1 was thermal in nature, and discovered several bright X-ray sources in the southern sky. He designed detectors which operated in the soft (below 1 keV) X-ray energy band and showed that old supernova remnants emitted copiously in that energy band.

In 1976 Seward used the Ariel 5 satellite to discover X-ray emission from the unusual object SS 433, later identified as the first known microquasar.

In 1977 Seward moved to the Smithsonian Astrophysical Observatory to join the HEAO-B project, renamed the Einstein Observatory after its launch in 1978. Prior to Einstein, an astronomy satellite's data was reserved for the use of the developers of the satellite's instruments. With the new satellite (along with the International Ultraviolet Explorer mission which introduced the practice around the same time) any astronomer in the world could apply for observng time. Seward led the user support team and established the policies for supporting such external observers that have served as the template for subsequent missions. Seward played a similar role in setting up user support for the Chandra X-ray Observatory.

In 1995 Seward, with Phil Charles, wrote a well-regarded textbook on X-ray astronomy, Exploring the X-ray Universe

Seward formally retired in 2005 but as of 2023 continued to carry out active research on X-ray supernova remnants.