A Space-based All-sky MeV gamma-ray Survey with the Electron Tracking Compton Camera

TL;DR

This paper discusses a proposed space-based all-sky MeV gamma-ray survey using advanced Electron Tracking Compton Cameras (ETCCs) to improve imaging and background reduction, with promising preliminary balloon flight results.

Contribution

It introduces the concept of a space-based all-sky MeV gamma-ray survey utilizing ETCC technology, highlighting its potential to significantly advance astrophysical observations.

Findings

Successful detection of diffuse continuum emission from Galactic Center

Detection of 511 keV annihilation line with high significance

Demonstrated feasibility of ETCCs for space-based gamma-ray astronomy

Abstract

A sensitive survey of the MeV gamma-ray sky is needed to understand important astrophysical problems such as gamma-ray bursts in the early universe, progenitors of Type Ia supernovae, and the nature of dark matter. However, the study has not progressed remarkably since the limited survey by COMPTEL onboard CGRO in the 1990s. Tanimori et al. have developed a Compton camera that tracks the trajectory of each recoil electron in addition to the information obtained by the conventional Compton cameras, leading to superior imaging. This Electron Tracking Compton Camera (ETCC) facilitates accurate reconstruction of the incoming direction of each MeV photon from a wide sky at ~degree angular resolution and with minimized particle background using trajectory information. The latest ETCC model, SMILE-2+, made successful astronomical observations during a day balloon flight in 2018 April and detected diffuse continuum and 511 keV annihilation line emission from the Galactic Center region at a high significance in ~2.5 hours. We believe that MeV observations from space with upgraded ETCCs will dramatically improve our knowledge of the MeV universe. We advocate for a space-based all-sky survey mission with multiple ETCCs onboard and detail its expected benefits.