Professor Bradt joined the Department of Physics as an Instructor in 1961, was promoted to Assistant Professor in 1963, to Associate Professor in 1968, to Professor in 1972, and became Professor Emeritus in 2001. A music major, he earned his A.B. from Princeton University in 1952 and his Ph.D. in Physics from MIT in 1961. Bradt founded MIT’s sounding rocket program in X-ray astronomy in 1967, was a co-Investigator on the MIT SAS-3 mission (launched in 1975), was a co-Principal Investigator on the High-Energy Astronomy Observatory, HEAO-1 (1977). He was Principal Investigator of the All-Sky-Monitor (ASM) instrument on the Rossi X-ray Timing Explorer (RXTE, 1995), which is still operating in 2010. Bradt’s work has long been directed toward the determination of X-ray source positions and the follow-up studies of the objects identified. With students and associates, he has carried out studies with RXTE of the unusual neutron-star binary Cir X-1, of gamma-ray bursts, and of the behavior of transient X-ray sources.

Bradt served terms as the Secretary/Treasurer and Chairman of the High Energy Astrophysics Division (HEAD) of the American Astronomical Society (AAS) in the 1970s. He was awarded the Buechner Teaching Prize of the MIT Physics Department in 1990 and was the 1999 co-recipient of the Rossi Prize of the HEAD/AAS for his role in bringing about the RXTE mission and the results forthcoming from it.

After retirement, Bradt has focused on textbook writing. Astronomy Methods was published by Cambridge University Press in 2004 and Astrophysics Processes in 2008. Currently (2010), he is editing his father’s letters from the Pacific during World War II.

RXTE, an earth-orbiting X-ray astronomy observatory , studies X-ray emission from black-holes and neutron stars with high statistics so the plasmas in their vicinities can be studied with time resolutions comparable to the dynamical time constants of matter in the deep potential wells. The mission, among other important results, has revealed the presence of accreting X-ray pulsars (neutron stars) with spin periods of a few milliseconds. It has also demonstrated a link between accretion and jet formation in (black-hole) “microquasars.” Microquasars are black-hole accretors in the Milky-Way Galaxy which exhibit pronounced radio jets, as do their more massive and distant counterparts, the well known extragalactic quasars. The mission is completing its fifteenth year of productive observations (in Dec. 2010), but will soon come to an end.