| 1. |
- Arimoto, M., et al.
(författare)
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Performance assessment study of the balloon-borne astronomical soft gamma-ray polarimeter PoGOLite
- 2007
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 40:2, s. 438-441
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of polarization play a crucial role in the understanding of the dominant emission mechanism of astronomical sources. Polarized Gamma-ray Observer-Light version (PoGOLite) is a balloon-borne astronomical soft gamma-ray polarimeter at the 25-80 keV band. The PoGOLite detector consists of a hexagonal close-packed array of 217 Phoswich detector cells (PDCs) and side anti-coincidence shields (SASs) made of BGO crystals surrounding PDCs. Each PDC consists of a slow hollow scintillator, a fast scintillator and a BGO crystal that connects to a photomultiplier tube at the end. To examine the PoGOLite's capability and estimate the performance, we conducted experiments with the PDC using radioisotope 241Am. In addition, we compared this result with performance expected by Monte Carlo simulation with Geant4. As a result, we found that the actual PDC has the capability to detect a 100 m Crab source until 80 keV.
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| 2. |
- Axelsson, Magnus, et al.
(författare)
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Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite
- 2007
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Ingår i: Astroparticle Physics. - : Elsevier BV. - 0927-6505. ; 28:3, s. 327-337
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Tidskriftsartikel (refereegranskat)abstract
- Linear polarization in X- and γ-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper, we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25–100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 h were simulated, corresponding to a standard and a long duration flight, respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.
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| 3. |
- Jackson, Miranda, et al.
(författare)
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PoGOLite : a balloon-borne soft gamma-ray polarimeter
- 2009
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Ingår i: 2009 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-5. - 9781424439614 ; , s. 449-453
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Konferensbidrag (refereegranskat)abstract
- PoGOLite is a balloon-borne X-ray polarimeter, designed to measure the polarization of 25-80 keV X-rays. It is scheduled for a pathfinder flight in August 2010. This paper outlines the scientific motivation and the status of preparations of the payload.
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| 4. |
- Kamae, Tuneyoshi, et al.
(författare)
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PoGOLite - A high sensitivity balloon-borne soft gamma-ray polarimeter
- 2008
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 30:2, s. 72-84
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Tidskriftsartikel (refereegranskat)abstract
- We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 and 80 keV in one 6-h flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow Held of view (FWHM = 1.25 msr, 2.0 deg x 2.0 deg) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (similar to 228 cm(2) at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm(2) indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a similar to 100 mCrab source between 25 and 50 keV. A 6-h observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter.
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| 5. |
- Kiss, Mózsi Bank, et al.
(författare)
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PoGOLite : Opening a new window on the universe with polarized gamma-rays
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 580:2, s. 876-879
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Tidskriftsartikel (refereegranskat)abstract
- PoGOLite (the Polarized Gamma-ray Observer, light-weight version) is a balloon-borne instrument that will measure the polarization of soft gamma-rays in the energy range 25-100keV from various astronomical sources such as pulsars, active galactic nuclei, galactic X-ray binaries and accreting black holes. The polarization properties of such radiation can reveal important new information about the geometry, magnetic fields and the emission mechanisms of the observed sources. The first flight is scheduled for 2009. In this paper, we present the current state of the project.
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| 6. |
- Kiss, Mózsi
(författare)
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Studies of PoGOLite performance and background rejection capabilities
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Polarized Gamma-ray Observer (PoGOLite) is a balloon-borne instrument capable of measuring as low as 10% polarization from a 200 mCrab source in a sixhour °ight. A wide array of sources can be studied, including pulsars, neutron stars, accretion discs and jets from active galactic nuclei. The two new observational parameters provided by such measurements, polarization angle and degree, will allow these objects to be studied in a completely new way, providing information both about the emission mechanisms and the geometries of the emitting objects. The instrument measures anisotropies in azimuthal scattering angles of gammarays with a close-packed array of 217 well-type phoswich detector cells (PDCs) by coincident detection of Compton scattering and photoelectric absorption. Each PDC comprises a \slow" plastic scintillator tube, a \fast" plastic scintillator rod and a BGO crystal. The fast scintillator is the main detector component, whereas the slow scintillator and the BGO crystal act as an active collimator and a bottom anticoincidence shield, respectively. The three parts are viewed by a single photomultiplier tube (PMT) and pulse shape discrimination is used to identify signals from each part. The detector array is surrounded by a 54-segment side anticoincidence shield (SAS) made of BGO crystals. Each segment is 60 cm long and consists of three crystals. A total of 187 crystals have been procured and tested for light yield, energy resolution, dimensions and surface ¯nish. All crystals have been found to be of excellent quality and measured characteristics have been within speci¯ed limits. The performance of the instrument has also been evaluated in several beam tests with polarized synchrotron photons irradiating a prototype detector array. Front-end electronics have been tested and a modulation in the observed scattering angles has been observed in line with expectations. Geant4-based Monte Carlo simulations of the instrument performance have shown that a 10 cm thick polyethylene shield is required around the detector array in order to su±ciently reduce the background from atmospheric neutrons. To validate these simulations, a simple detector array with four plastic scintillators and three BGO crystals was irradiated with 14 MeV neutrons. The array was shielded with polyethylene, mimicking the PoGOLite instrument design. Measured results could be accurately recreated in Geant4 simulations, demonstrating that the treatment of neutron interaction processes in Geant4 is reliable.
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| 7. |
- Kiss, Mózsi, et al.
(författare)
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The PoGOLite balloon-borne soft gamma-ray polarimeter
- 2008
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Ingår i: COOL DISCS, HOT FLOWS. - : AIP. ; , s. 225-232
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Konferensbidrag (refereegranskat)abstract
- Linearly polarized radiation in the hard X-ray/soft gamma-ray band is expected from a large variety of astronomical sources. We discuss the importance of polarimetric studies for several classes of sources - pulsars, accreting black holes. magnetic neutron stars and jets from active galaxies - and then describe PoGOLite, a balloon-borne instrument which is currently under construction and will be able to measure the polarization of electromagnetic radiation from such extra-solar objects in the energy range 25-80 keV.
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| 8. |
- Kiss, Mózsi, 1982-
(författare)
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The PoGOLite balloon-borne soft gamma-ray polarimeter
- 2008
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Ingår i: Astroparticle, Particle and Space Physics, Detectors and Medical Physics Applications. - : World Scientific. - 9789812819086 ; , s. 886-890
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Konferensbidrag (refereegranskat)abstract
- PoGOLite is a balloon-borne experiment that will measure the polarization of soft gamma-rays between 25 keV and 80 keV through detection of coincident Compton scattering and absorption in a close-packed array of 217 well-type phoswich detector cells. The potential observation targets include pulsars, accreting compact objects and astrophysical jets. The polarization properties of such radiation can reveal important new information on the geometry, magnetic fields and emission mechanisms of these sources.
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| 9. |
- Marini Bettolo, Cecilia, et al.
(författare)
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The BGO anticoincidence system of the PoGOLite balloon-borne soft gamma-ray polarimeter
- 2007
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Ingår i: Proceedings of the 30th International Cosmic Ray Conference, ICRC 2007. - : Universidad Nacional Autonoma de Mexico. ; , s. 483-486
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Konferensbidrag (refereegranskat)abstract
- The PoGOLite balloon-borne experiment applies well-type phoswich detector technology tomeasurements of soft gamma-ray polarization in the 25 keV - 80 keV energy range. The polarization isdetermined using Compton scattering and photoelectric absorption in an array of 217 plastic scintillators.This sensitive volume is surrounded by a segmented bismuth germanate oxide (BGO) anticoincidenceshield, designed to reduce background from charged cosmic rays, primary and atmospheric gamma-rays,and atmospheric and instrumental neutrons. A total of 379 BGO crystals with three different geometriesare used, giving an overall mass of approximately 250 kg. Tests of the BGO crystals are described andthe overall design of the anticoincidence shield is reviewed.
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| 10. |
- Mizuno, T., et al.
(författare)
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A Monte Carlo method for calculating the energy response of plastic scintillators to polarized photons below 100 keV
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 600:3, s. 609-617
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Tidskriftsartikel (refereegranskat)abstract
- The energy response of plastic scintillators (Eljen Technology EJ-204) to polarized soft gamma-ray photons below 100 keV has been studied, primarily for the balloon-borne polarimeter, PoGOLite. The response calculation includes quenching effects due to low-energy recoil electrons and the position dependence of the light collection efficiency in a 20 cm long scintillator rod. The broadening of the pulse-height spectrum, presumably caused by light transportation processes inside the scintillator, as well as the generation and multiplication of photoelectrons in the photomultiplier tube, were studied experimentally and have also been taken into account. A Monte Carlo simulation based on the Geant4 toolkit was used to model photon interactions in the scintillators. When using the polarized Compton/Rayleigh scattering processes previously corrected by the authors, scintillator spectra and angular distributions of scattered polarized photons could clearly be reproduced, in agreement with the results obtained at a synchrotron beam test conducted at the KEK Photon Factory. Our simulation successfully reproduces the modulation factor, defined as the ratio of the amplitude to the mean of the distribution of the azimuthal scattering angles, within similar to 5% (relative). Although primarily developed for the PoGOLite mission, the method presented here is also relevant for other missions aiming to measure polarization from astronomical objects using plastic scintillator scatterers.
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