An Electron-Tracking Compton Telescope for a Survey of the Deep Universe by MeV gamma-rays

Abstract

Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which are originated from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected mere $\sim 30$ persistent sources. It is in stark contrast with $\sim$2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be indeed helpful to reduce the background under conditions similar to space. Accordingly the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below $1\times 10^{-12}$ erg cm${}^{-2}$ s${}^{-1}$ at 1 MeV.

19 pages, 12 figures, Accepted to the Astrophysical Journal

References in corpus (5)

• Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J
• Gamma-ray diagnostics of Type Ia supernovae: Predictions of observables from three-dimensional modeling
• Probing the Cosmic X-ray and MeV Gamma-ray Background Radiation through the Anisotropy
• Development of a 30 cm-cube Electron-Tracking Compton Camera for the SMILE-II Experiment
• Performance of a new electron-tracking Compton camera under intense radiations from a water target irradiated with a proton beam

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• Development of Convolutional Neural Networks for an Electron-Tracking Compton Camera
• Radioactively-Powered Gamma-Ray Transient Associated with a Kilonova from Neutron Star Merger
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• Possibility of Systematic Study of Supernova Explosions by Nuclear Imaging Spectroscopy