Mark E. Bandstra

Position Calibrations and Preliminary Angular Resolution of the Prototype Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and gamma ray polarization. A prototype instrument was successfully launched from Ft. Sumner, NM on June 1, 2005. The NCT prototype consists of two 3D position sensitive High-Purity-Germanium (HPGe) strip detectors fabricated with amorphous Ge contacts. The novel ultra-compact design and new technologies allow NCT to achieve high efficiencies with excellent spectral resolution and background reduction. We have completed our preliminary calibrations of both the energy and the 3D position of interactions for the prototype instrument. Determination of both the energy and the position is crucial for Compton imaging, and minimizing the errors in each improves the angular resolution. Because of the compact design of the detectors and the high spectral resolution of germanium, we expect the position uncertainties to dominate over energy uncertainties when determining the angular resolution. Detailed depth calibrations and a preliminary determination of angular resolution as a function of energy are described. We determine how measurement uncertainties and physical limitations (energy uncertainty, position uncertainty, Doppler broadening, and systematics) constrain the ultimate angular resolution.

First results from the balloon flight of the NCT prototype

We flew a prototype of the Nuclear Compton Telescope (NCT) on a high altitude balloon from Fort Sumner, New Mexico on 2005 June 1. The NCT prototype is a soft gamma-ray (0.2-15 MeV) telescope designed to study, through spectroscopy, imaging, and timing, astrophysical sources of nuclear line emission and gamma-ray polarization. Our program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope satellite, while studying gamma-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. The NCT prototype utilizes two, 3D imaging germanium detectors (GeDs) in a novel, ultra-compact design optimized for nuclear line emission (0.5-2 MeV) and polarization in the 0.2-0.5 MeV range. Our prototype flight was a critical test of the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes.

Pre-flight calibration of the prototype Nuclear Compton Telescope

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2MeV-10MeV) telescope designed to study astrophysical sources of nuclear line emission and polarization. A prototype instrument was successfully launched from Ft. Sumner, NM on June 1, 2005. The NCT prototype consists of two 3D position sensitive High-Purity-Germanium (HPGe) strip detectors fabricated with amorphous Ge contacts. The novel ultra-compact design and new technologies allow NCT to achieve high efficiencies with excellent spectral resolution and background reduction. Energy and positioning calibration data was acquired pre-flight in Fort Sumner, NM after the full instrument integration. Here we discuss our calibration techniques and results, and detector efficiencies. Comparisons with simulations are presented as well.

The upcoming long duration balloon flight of the Nuclear Compton Telescope

The nuclear Compton telescope (NCT) is a balloon- borne soft gamma-ray (0.2 MeV-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and polarization. A prototype instrument was successfully launched from Fort Sumner, New Mexico on June 1, 2005. The NCT prototype consisted of two 3D position sensitive high-purity germanium strip detectors (GeDs) fabricated with amorphous Ge contacts. We are currently working toward two balloon flights: another conventional balloon flight from Fort Sumner, New Mexico in September 2008, and a long-duration balloon flight (LDBF) from Alice Springs, Australia in December 2009. The NCT instrument is being upgraded to include all twelve planned GeDs. The electronics for all twelve detectors have been redesigned for smaller size, lower power consumption, and lower noise, and are now being fabricated and tested. Here we present our current progress in preparing for the flights.

Spectral Analysis of GRBs Measured by RHESSI

The Ge spectrometer of the RHESSI satellite is sensitive to Gamma Ray Bursts (GRBs) from about 40 keV up to 17 MeV, thus ideally complementing the Swift/BAT instrument whose sensitivity decreases above 150 keV. We present preliminary results of spectral fits of RHESSI GRB data. After describing our method, the RHESSI results are discussed and compared with Swift and Konus.