MEGA: a medium-energy gamma-ray astronomy mission concept

Abstract

The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky (0.4 -50 MeV) and bridge the huge sensitivity gap between the COMPTEL and OSSE experiments on the Compton Gamma Ray Observatory, the SPI and IBIS instruments on INTEGRAL, and the visionary Advanced Compton Telescope (ACT) mission. The scientific goals include, among other things, compiling a much larger catalog of sources in this energy range, performing far deeper searches for supernovae, better measuring the galactic continuum and line emissions, and identifying the components of the cosmic diffuse gamma-ray emission. MEGA will accomplish these goals using a tracker made of Si strip detector (SSD) planes surrounded by a dense high-Z calorimeter. At lower photon energies (below ∼ 30 MeV), the design is sensitive to Compton interactions, with the SSD system serving as a scattering medium that also detects and measures the Compton recoil energy deposit. If the energy of the recoil electron is sufficiently high (> 2 MeV) its momentum vector can also be measured. At higher photon energies (above ∼10 MeV), the design is sensitive to pair production events, with the SSD system measuring the tracks of the electron and positron. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results from the prototype and describe the proposed satellite mission. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Continuum Sensitivity * [MeV cm2 s1] TObS=106 s = E le-2 le-3 COS-B le-4 le-5 spi le-6 le-7 le-5 aol o.i 1 10 100 Energy (MeV) Figure 1. Sensitivity curves for recent and current gamma-ray and X-ray telescopes, showing the sensitivity goal for a MEGA satellite mission.

Monte Carlo simulations of gamma-ray space telescopes: a BoGEMMS multi-purpose application

“…These measurements, coupled with the energy and direction of the scattered Gamma-ray photon collected by the high Z scintillation detector (the calorimeter) placed below the tracker, allow to indirectly measure the energy and direction of the primary photon. The use of electron tracking Compton telescopes is a very recent and still in progress technique, and it is the core of the proposed MEGA 16 and Gamma-Light telescopes. Above 30-40 MeV, the pair production comes into play, with the photon annihilating into an electron/positron pair, the threshold for the interaction being 1.02 MeV (∼ 2m e ), with the energy of the photon taken up by the pair as rest mass and kinetic energy.…”