Article

# The sky distribution of positronium annihilation continuum emission measured with SPI/INTEGRAL

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(Impact Factor: 4.38). 01/2006; 450(3). DOI: 10.1051/0004-6361:20054046
Source: arXiv

ABSTRACT

We present a measurement of the sky distribution of positronium (Ps) annihilation continuum emission obtained with the SPI spectrometer on board ESA's INTEGRAL observatory. The only sky region from which significant Ps continuum emission is detected is the Galactic bulge. The Ps continuum emission is circularly symmetric about the Galactic centre, with an extension of about 8 deg FWHM. Within measurement uncertainties, the sky distribution of the Ps continuum emission is consistent with that found by us for the 511 keV electron-positron annihilation line using SPI. Assuming that 511 keV line and Ps continuum emission follow the same spatial distribution, we derive a Ps fraction of 0.92 +/- 0.09. These results strengthen our conclusions regarding the origin of positrons in our Galaxy based on observations of the 511 keV line. In particular, they suggest that the main source of Galactic positrons is associated with an old stellar population, such as Type Ia supernovae, classical novae, or low-mass X-ray binaries. Light dark matter is a possible alternative source of positrons. Comment: accepted for publication by A&A

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Available from: Christoph Winkler, Dec 22, 2012
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• "Gamma rays with energies of 100 keV to 1 MeV are expected to provide valuable insight into unexplained celestial phenomena, such as nucleosynthesis in supernovae [2], particle acceleration in active galactic nuclei [3] and gamma ray bursts [4]. Therefore, gamma rays in this energy band are of immense interest to astronomers. "
##### Article: Performance of a new Electron-Tracking Compton Camera under intense radiations from a water target irradiated with a proton beam
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ABSTRACT: We have developed an electron-tracking Compton camera (ETCC) for use in next-generation MeV gamma ray telescopes. An ETCC consists of a gaseous time projection chamber (TPC) and pixel scintillator arrays (PSAs). Since the TPC measures the three dimensional tracks of Compton-recoil electrons, the ETCC can completely reconstruct the incident gamma rays. Moreover, the ETCC demonstrates efficient background rejection power in Compton-kinematics tests, identifies particle from the energy deposit rate (dE/dX) registered in the TPC, and provides high quality imaging by completely reconstructing the Compton scattering process. We are planning the "Sub-MeV gamma ray Imaging Loaded-on-balloon Experiment" (SMILE) for our proposed all-sky survey satellite. Performance tests of a mid-sized 30 cm-cubic ETCC, constructed for observing the Crab nebula, are ongoing. However, observations at balloon altitudes or satellite orbits are obstructed by radiation background from the atmosphere and the detector itself. The background rejection power was checked using proton accelerator experiments conducted at the Research Center for Nuclear Physics, Osaka University. To create the intense radiation fields encountered in space, which comprise gamma rays, neutrons, protons, and other energetic entities, we irradiated a water target with a 140 MeV proton beam and placed a SMILE-II ETCC near the target. In this situation, the counting rate was five times than that expected at the balloon altitude. Nonetheless, the ETCC stably operated and identified particles sufficiently to obtain a clear gamma ray image of the checking source. Here, we report the performance of our detector and demonstrate its effective background rejection based in electron tracking experiments.
Journal of Instrumentation 12/2014; 10(01). DOI:10.1088/1748-0221/10/01/C01053 · 1.40 Impact Factor
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• "In astronomy, it is interesting to observe MeV gamma rays emitted from celestial objects since this energy range is a unique window to observe nucleosynthesis in supernovae using gamma ray lines from nuclear de-excitation [1]–[6], electron-positron pair annihilation from the galactic center [7]– [9], and neutron captures which occur in solar flares [10]. In addition, there are gamma rays produced by synchrotron radiation or inverse Compton-scattering in gamma-ray pulsars [11]–[14], active galactic nuclei (AGN) [15]–[19], and gamma ray bursts (GRB) [20]–[22]. "
##### Article: SMILE: A balloon-borne sub-MeV/MeV gamma-ray Compton Camera using an Electron-Tracking gaseous TPC and a scintillation camera
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ABSTRACT: We have developed an Electron-Tracking Compton Camera (ETCC) for use onboard a balloon to observe sub-MeV/MeV gamma rays from celestial objects. The ETCC is constructed with a three dimensional gaseous tracker for recoil electrons from Compton scattering, and GSO:Ce pixel scintillator arrays as absorber of the Compton-scattered gamma-ray. By using the ETCC, we can reconstruct the energy and direction of individual gamma rays. We have developed a prototype ETCC with a (30 cm)3 TPC, and tested its performance in the range of 356 - 835 keV in the laboratory. As the result, we succeeded in taking images of gamma ray sources and determined a detection efficiency of 9.0 × 10−6 and an effective area of 8.0 × 10−3 cm2 at 662 keV for the prototype ETCC. Furthermore, we developed a new power saving readout circuit for the scintillators that achieves the electric power consumption of 0.41 W/channel, an energy dynamic range of 81 - 1333 keV, and an energy resolution of 10.3% at full width at half maximum at 662 keV.
Journal of Instrumentation 01/2012; 7(01):C01088. DOI:10.1088/1748-0221/7/01/C01088 · 1.40 Impact Factor
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• "The emission from positron annihilations in interstellar space has been mapped across the sky, and consolidated earlier hints for the bulge region of the Galaxy being by far the brightest emission region on the sky [18] [57] [58]. These maps revealed a surprisingly-symmetric bulge emission, and barely were able to detect annihilation emission from the Galaxy's disk, where most of the candidate sources are located (see [7] for a review, and Churazov et al., this volume). "
##### Article: The extreme sky - Seven years of INTEGRAL
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ABSTRACT: Seven years of successful observations of the sky have been completed within the INTEGRAL mission, in the transition regime between X-rays and gamma-rays from ~10-8000 keV. Initially-agreed mission goals have been pursued, and both high-resolution images of point sources and high-resolution spectra of nuclear lines have been obtained. New discoveries have been made, such as X-ray emission from embedded binaries, hard emission tails from AXPs and 60Fe radioactivity lines; these stimulated both theoretical and observational studies, and now make INTEGRAL a valuable asset for the astronomical survey of high-energy sources across the sky. This contribution summarizes the situation after seven years of the mission, and concludes the 7-year anniversary workshop "The extreme sky" held in Otranto, Italy, in Oct 2009. Comment: 12 pages, 3 figures; Concluding remarks of the INTEGRAL workshop "The Exterme Sky" held in Otranto, Puglia, in Oct 2009