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

Abstract

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 2 π 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 foundmore » 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 10{sup 7} s exposure and over 20 GRBs down to a 6 × 10{sup −6} erg cm{sup −2} fluence and 10% polarization during a one-year observation.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;  [1];  [2];  [3];  [4]
  1. Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502 (Japan)
  2. New Industry Creation Hatchery Center (NICHe), Tohoku University, Sendai, Miyagi, 980-8579 (Japan)
  3. Department of Physics, Kobe University, Kobe, Hyogo, 658-8501 (Japan)
  4. College of Science and Engineering, School of Mathematics and Physics, Kanazawa University, Kanazawa, Ishikawa, 920-1192 (Japan)
Publication Date:
OSTI Identifier:
22661146
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 839; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BEAMS; BLACK HOLES; CONFIGURATION; COSMIC GAMMA BURSTS; ELECTRONS; GAMMA RADIATION; KEV RANGE; MEV RANGE; MODULATION; POLARIMETERS; POLARIMETRY; POLARIZATION; SATELLITES; SIMULATION; SPRING-8 STORAGE RING; STABILITY; TELESCOPES; X RADIATION

Citation Formats

Komura, S., Takada, A., Mizumura, Y., Miyamoto, S., Takemura, T., Kishimoto, T., Kubo, H., Matsuoka, Y., Mizumoto, T., Nakamasu, Y., Nakamura, K., Oda, M., Parker, J. D., Sonoda, S., Tanimori, T., Tomono, D., Yoshikawa, K., Kurosawa, S., Miuchi, K., and Sawano, T., E-mail: komura@cr.scphys.kyoto-u.ac.jp. Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA68DC.
Komura, S., Takada, A., Mizumura, Y., Miyamoto, S., Takemura, T., Kishimoto, T., Kubo, H., Matsuoka, Y., Mizumoto, T., Nakamasu, Y., Nakamura, K., Oda, M., Parker, J. D., Sonoda, S., Tanimori, T., Tomono, D., Yoshikawa, K., Kurosawa, S., Miuchi, K., & Sawano, T., E-mail: komura@cr.scphys.kyoto-u.ac.jp. Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera. United States. doi:10.3847/1538-4357/AA68DC.
Komura, S., Takada, A., Mizumura, Y., Miyamoto, S., Takemura, T., Kishimoto, T., Kubo, H., Matsuoka, Y., Mizumoto, T., Nakamasu, Y., Nakamura, K., Oda, M., Parker, J. D., Sonoda, S., Tanimori, T., Tomono, D., Yoshikawa, K., Kurosawa, S., Miuchi, K., and Sawano, T., E-mail: komura@cr.scphys.kyoto-u.ac.jp. Mon . "Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera". United States. doi:10.3847/1538-4357/AA68DC.
@article{osti_22661146,
title = {Imaging Polarimeter for a Sub-MeV Gamma-Ray All-sky Survey Using an Electron-tracking Compton Camera},
author = {Komura, S. and Takada, A. and Mizumura, Y. and Miyamoto, S. and Takemura, T. and Kishimoto, T. and Kubo, H. and Matsuoka, Y. and Mizumoto, T. and Nakamasu, Y. and Nakamura, K. and Oda, M. and Parker, J. D. and Sonoda, S. and Tanimori, T. and Tomono, D. and Yoshikawa, K. and Kurosawa, S. and Miuchi, K. and Sawano, T., E-mail: komura@cr.scphys.kyoto-u.ac.jp},
abstractNote = {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 2 π 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 10{sup 7} s exposure and over 20 GRBs down to a 6 × 10{sup −6} erg cm{sup −2} fluence and 10% polarization during a one-year observation.},
doi = {10.3847/1538-4357/AA68DC},
journal = {Astrophysical Journal},
number = 1,
volume = 839,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2017},
month = {Mon Apr 10 00:00:00 EDT 2017}
}
  • GRBs have been recently known as a unique probe to catch the highest z galaxies and stars. Here I propose the new trigger method to catch high-z GRBs with z>10 efficiently by imaging sub-MeV gamma rays from GRBs. We have developed the Electron Tracking Compton Camera (ETCC) with reconstructing tracks of the recoil electron in Compton process to explore the MeV gamma-ray astronomy. By measuring the track of a recoil electron, the direction of the incident gamma ray is determined for each photon, which enables us to reconstruct the direction of GRBs by detecting only several ten photons (>100 keV).more » Ability of the large ETCC (100 cm{sup 2} effective area) to detect GRBs with z{approx}20 is revealed, based on the results of the balloon experiment and laboratory imaging test using the small ETCC.« less
  • Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which originate 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 a mere ∼30 persistent sources. It is in stark contrast with the ∼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 stagnationmore » in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3D 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 helpful to reduce the background under conditions similar to those in 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 × 10{sup −12} erg cm{sup −2} s{sup −1} at 1 MeV.« less
  • Parameters which govern the choice of a detection system to measure the linear polarization of {gamma} rays at low energies are discussed. An integrated polarimeter is described which is constructed from a single crystal of germanium. It is a compact planar device with the sectors defined electrically, and which gives an energy resolution in the add-back mode of 1 keV at 300 keV. Its performance is demonstrated in a series of calibration measurements using both unpolarized radiation from radioactive sources and polarized {gamma} rays from the {sup 168}Er({alpha},2{ital n}){sup 170}Yb reaction at {ital E}{sub {alpha}}=25 MeV. Polarization measurements at energiesmore » as low as 84 keV have been achieved, where the sensitivity was 0.32{plus_minus}0.09. The sensitivity, efficiency, and energy resolution are reported. Our results indicate that energy resolution should be included in the definition of the figure of merit and we relate the new definition to earlier work. The comparisons show the advantages of the present design in the energy range below 300 keV and its competitiveness up to 1500 keV. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
  • We observed diffuse cosmic and atmospheric gamma rays at balloon altitudes with the Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment I (SMILE-I) as the first step toward a future all-sky survey with a high sensitivity. SMILE-I employed an electron-tracking Compton camera comprised of a gaseous electron tracker as a Compton-scattering target and a scintillation camera as an absorber. The balloon carrying the SMILE-I detector was launched from the Sanriku Balloon Center of the Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency on 2006 September 1, and the flight lasted for 6.8 hr, including level flight for 4.1 hr at an altitudemore » of 32-35 km. During the level flight, we successfully detected 420 downward gamma rays between 100 keV and 1 MeV at zenith angles below 60 deg. To obtain the flux of diffuse cosmic gamma rays, we first simulated their scattering in the atmosphere using Geant4, and for gamma rays detected at an atmospheric depth of 7.0 g cm{sup -2} we found that 50% and 21% of the gamma rays at energies of 150 keV and 1 MeV, respectively, were scattered in the atmosphere prior to reaching the detector. Moreover, by using Geant4 simulations and the QinetiQ atmospheric radiation model, we estimated that the detected events consisted of diffuse cosmic and atmospheric gamma rays (79%), secondary photons produced in the instrument through the interaction between cosmic rays and materials surrounding the detector (19%), and other particles (2%). The obtained growth curve was comparable to Ling's model, and the fluxes of diffuse cosmic and atmospheric gamma rays were consistent with the results of previous experiments. The expected detection sensitivity of a future SMILE experiment measuring gamma rays between 150 keV and 20 MeV was estimated from our SMILE-I results and was found to be 10 times better than that of other experiments at around 1 MeV.« less
  • No abstract prepared.