Who I Am

I am a research scientist in gamma-ray astronomy active in instrument development and data analysis, and dabbling in theory. I have a wife, two children and I like mountaineering.

What I Do

I am the Principal Investigator for Swift, a NASA satellite which will detect gamma ray bursts, determine their location and even their distance. Swift is due to launch in 2003 I am also the Deputy Project Scientist for GLAST, the Gamma Ray Large Area Space Telescope, and head of the Gamma Ray and Cosmic Ray Astrophysics Branch at the Goddard Space Flight Center. My interests include gamma-ray bursts, nuclear astrophysics, active galactic nuclei, black hole binaries and pulsars. pulsars.

Gamma Rays Bursts, Active Galactic Nuclei and Black Hole Binaries

Beginning in 2003, the Swift satellite will observe GRBs in x-rays, optical and ultraviolet light, determine accurate positions of the GRBs, examine their afterglow to get a distance, and produce a lightcurve (a graph of brightness versus time) at different wavelengths. Sometime after 2005, GLAST will observe the gamma rays emitted by GRBs, and also extend our knowledge of these exotic objects.

Active Galactic Nuclei
Our Galaxy, the Milky Way, may seem like a quiet place, but not all galaxies are calm. Some have extremely bright cores, indicating a lot of activity is taking place there. Observations with ground based telescopes and with Hubble have confirmed that many if not most galaxies harbor a supermassive black hole in their centers; our own Milky Way does as well. If conditions are right, the gas and dust in a galaxy will spiral into the black hole. As it falls in, a disk of material forms. Friction inside that accretion disk can generate enough energy to heat the material until it glows in x-rays. We call these Active Galactic Nuclei, or AGNs. They also have jets of matter spewing out at a large fraction of the speed of light. GLAST again will help us map these jets and nuclei out at high energies, allowing us to study them in ways we haven't been able to in the past.

Black Hole Binaries
Note all black holes are huge. Stellar black holes have masses about 3 or more times the mass of the Sun. Many exist in binary systems, that is, a pair of stars orbiting each other. If a black hole is orbiting another star, it can capture the solar wind from that star, or even tear matter form the surface of the star itself. Like a smaller version of an AGN, that infalling matter can form a disk and emit x rays, as well as form jets of matter streaming out. We are only just now beginning to understand these objects, and observations with GLAST will no doubt both increase our knowledge of them and whet our appetites for more.