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 Dr. Boldt's undergraduate college education was in physics at MIT. He continued at MIT for his graduate studies. Rossi's group during the time when new elementary particles were being discovered among cosmic rays and experiments were just starting on their detailed study when produced "artificially" via high energy accelerators. His PhD thesis (1958, with D. Caldwell) concerned the Lambda hyperon. Before coming to Goddard he taught physics at Rutgers, worked in the cosmic ray lab at Princeton (during the epoch when T. Bowen, J. Cronin, V. Fitch and R. Giacconi were there) and studied K mesons at Saturne, the proton synchrotron at Saclay, France. When he came to F. McDonald's lab at Goddard he worked with V. K. Balasubrahmanyan et al. in studying new satellite data on subrelativistic cosmic rays and attempting to understand their severe modulation by the solar wind. Since the interstellar flux of these subrelativistic cosmic rays could be much greater than that directly observed near Earth orbit in the solar system, he investigated the possibility of observing their in-situ effects by other means. In particular, he noted that their ionization of the cool interstellar gas would lead to an appreciable flux of narrow spectral lines (H-alpha, H-beta) from recombining hydrogen ions and suggested (with P. Serlemitsos) that knock-on electrons from the ionization process itself would yield X-radiation having a spectrum characteristic of the cosmic ray nuclei involved. At his initiation, the first work on observing narrow H-alpha and H-beta lines from interstellar hydrogen was carried out here at Goddard (1970) using the telescope at the optical site and a Fabry-Perot "Pepsios" spectrometer from the University of Wisconsin; this became the thesis research of R. Reynolds and led to the highly successful comprehensive follow-up program that Reynolds and his associates at the University of Wisconsin (Madison) are still expanding. The search for X-rays indicative of subrelativistic cosmic ray ionization provided motivation for Goddard's HEAO-1 experiment on the X-ray background. Dr. Boldt initiated Goddard's X-ray astronomy program in 1965 with a series of balloon-borne experiments using gas proportional counters as well as the scintillation crystals usual to previous (gamma-ray) experiments. By the end of 1966 seven successful flights had been completed, five from New Mexico and two from Australia. The Australian flights were the first to identify hard X-ray emissions from the region of the galactic center; these observations formed the basis for the PhD thesis of G. Riegler, Boldt's first grad student at Goddard. Over the years, Dr. Boldt has been associated with the PhD thesis research in X-ray astronomy (based on balloon, rocket and satellite-borne experiments) of over a dozen UMCP (University of Maryland at College Park) students, most recently with T. Miyaji; Dr. Boldt is presently a UMCP Adjunct Professor of Physics. Dr. Boldt was a principal member of NASA scientific working groups that defined the HEAO-2 (Einstein Observatory) and AXAF (Chandra) X-ray telescope observatories and was a prime mover in getting Goddard to set the precedent of providing the high-throughput non-dispersive solid-state spectroscopy needed for such missions. Since the advent of Goddard's all-sky HEAO-1 experiment, for which he was principal investigator, his main research interests concern the cosmic X-ray background, its spectrum, isotropy and, with D. Leiter (as NRC associate), its possible origin via the spectral/luminosity evolution of AGN (Active Galactic Nuclei). With T. Miyaji, he has been investigating the X-radiation from AGN as a tracer of the total gravitational mass distribution in the present-epoch universe responsible for the peculiar motion of the Local Group (of galaxies). With C. Scharf, an NRC associate from England, and K. Jahoda he has investigated possible anisotropies in the available population of gamma-ray bursts in order to use the expected Compton-Getting effect as a diagnostic for distinguishing their origin as cosmological or galactic. In collaboration with M. Orlandini (Bologna, Italy) and J. Swank et al., Boldt is using the coincidence technique invented by B. Rossi to search for the microsecond temporal granularity expected in the X-ray emission from the neutron star surface of some wind-fed X-ray binary pulsars observed with the RXTE (Rossi X-ray Timing Explorer) mission. With M. Treyer, C. Scharf, O. Lahav, K. Jahoda, and T. Piran he is using a harmonic analysis of large scale fluctuations of the cosmic X-ray background to establish constraints on the structure of the Universe on scales of hundreds of Mpcs. With P. Ghosh (senior NRC associate from India), T. Hamilton (NRC associate), A. Levinson (Tel Aviv) , M. Loewenstein (U of MD & LHEA) and D. Torres (Princeton) Boldt is currently investigating observational evidence for a substantial population of dark quasar remnant supermassive black holes in the local universe. The precursor phenomena associated with such objects is being investigated by Boldt within the context of his participation in the mission definition advisory team for the LISA (Laser Interferometer Space Antenna) Observatory for gravitational radiation. Boldt and his collaborators are investigating the possibility that the dark cores of these quasar remnants harbor rotating black hole dynamos capable of generating high energy cosmic rays (>100 EeV). They advocate recognizing such dynamos by the pronounced curvature radiation of TeV gammas characteristic of the acceleration process associated with these otherwise dark objects, a potentially powerful new means for establishing which non-active galactic nuclei involve spinning supermassive black holes. During the last three decades Elihu Boldt has been the principal GSFC mentor for twenty post-doctoral NSF/NRC LHEA resident research associates and a comparable number of graduate students, several of whom are now playing leading roles at NASA facilities and other major research institutions. |