Fermi Gamma-ray Space Telescope

The Advanced Energetic Pair Telescope (AdEPT), a High Sensitivity Medium-Energy Gamma-Ray Polarimeter

T. M. Venters
S. D. Hunter, G. De Nolfo, A. R. Hanu, J. F. Krizmanic, F. W. Stecker, A. Timokhin

Abstract:

Many high-energy astrophysical phenomena exhibit unique, transitory behavior, such as spectral breaks, bursts, and flares below ~200 MeV. However, while significant progress in gamma-rays has been made by instruments such as Fermi and AGILE, a significant sensitivity gap remains in the medium-energy regime (0.75 - 200 MeV) that has been explored only by COMPTEL and EGRET on CGRO. Tapping into this unexplored regime requires development of a telescope with significant improvement in sensitivity. Our mission concept, covering ~5 to ~200 MeV, is the Advanced Energetic Pair Telescope (AdEPT). The AdEPT telescope will achieve angular resolution of ~0.6 deg at 70 MeV, similar to the angular resolution of Fermi/LAT at ~1 GeV that brought tremendous success in identifying new sources. AdEPT will also provide unprecedented polarization sensitivity, ~1% for a 1 Crab source. The enabling technology for AdEPT is the Three-Dimensional Track Imager (3-DTI) a low-density, large volume, gas time-projection chamber with a 2-dimensional readout. The 3-DTI provides high-resolution three-dimensional electron tracking with minimal Coulomb scattering that is essential to achieve high angular resolution and polarization sensitivity. We describe the design, fabrication, and performance of the 3-DTI detector, describe the development of a 50x50x100 cm3 AdEPT prototype, and highlight a few of the key science questions that AdEPT will address.