Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera

S. Komura, A. Takada, Y. Mizumura, S. Miyamoto, T. Takemura, T. Kishimoto, H. Kubo, S. Kurosawa, Y. Matsuoka, K. Miuchi, T. Mizumoto, Y. Nakamasu, K. Nakamura, M. Oda, J. D. Parker, T. Sawano, S. Sonoda, T. Tanimori, D. Tomono, K. Yoshikawa

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


X-ray and gamma-ray polarimetry is a promising tool to study the geometry and the magnetic configuration of various celestial objects, such as binary black holes or gamma-ray bursts (GRBs). However, statistically significant polarizations have been detected in few of the brightest objects. Even though future polarimeters using X-ray telescopes are expected to observe weak persistent sources, there are no effective approaches to survey transient and serendipitous sources with a wide field of view (FoV). Here we present an electron-tracking Compton camera (ETCC) as a highly sensitive gamma-ray imaging polarimeter. The ETCC provides powerful background rejection and a high modulation factor over an FoV of up to 2π sr thanks to its excellent imaging based on a well-defined point-spread function. Importantly, we demonstrated for the first time the stability of the modulation factor under realistic conditions of off-axis incidence and huge backgrounds using the SPring-8 polarized X-ray beam. The measured modulation factor of the ETCC was 0.65 ±0.01 at 150 keV for an off-axis incidence with an oblique angle of 30° and was not degraded compared to the 0.58 ±0.02 at 130 keV for on-axis incidence. These measured results are consistent with the simulation results. Consequently, we found that the satellite-ETCC proposed in Tanimori et al. would provide all-sky surveys of weak persistent sources of 13 mCrab with 10% polarization for a 107 s exposure and over 20 GRBs down to a 6 ×10-6 erg cm-2 fluence and 10% polarization during a one-year observation.

Original languageEnglish
Article number41
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2017 Apr 10


  • instrumentation: polarimeters
  • polarization
  • surveys


Dive into the research topics of 'Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera'. Together they form a unique fingerprint.

Cite this