| 1. |
- Arimoto, M., et al.
(författare)
-
Performance assessment study of the balloon-borne astronomical soft gamma-ray polarimeter PoGOLite
- 2007
-
Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 40:2, s. 438-441
-
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.
|
|
| 2. |
- Kanai, Y., et al.
(författare)
-
Beam test of a prototype phoswich detector assembly for the PoGOLite astronomical soft gamma-ray polarimeter
- 2007
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 570:1, s. 61-71
-
Tidskriftsartikel (refereegranskat)abstract
- We report about the beam test on a prototype of the balloon-based astronomical soft gamma-ray polarimeter, PoGOLite (Polarized Gamma-ray Observer-Light Version) conducted at KEK Photon Factory, a synchrotron radiation facility in Japan. The synchrotron beam was set at 30, 50, and 70 keV and its polarization was monitored by a calibrated polarimeter. The goal of the experiment was to validate the flight design of the polarimeter. PoGOLite is designed to measure polarization by detecting a Compton scattering and the subsequent photo-absorption in an array of 217 well-type phoswich detector cells (PDCs). The test setup included a first flight model PDC and a front-end electronics to select and reconstruct valid Compton scattering events. The experiment has verified that the flight PDC can detect recoil electrons and select valid Compton scattering events down to 30 keV from background. The measure azimuthal modulations (34.4%, 35.8% and 37.2% at 30, 50, and 70 keV, respectively) agreed within 10% (relative) with the predictions by Geant4 implemented with dependence on the initial and final photon polarizations.
|
|
| 3. |
- Mizuno, T., et al.
(författare)
-
High sensitivity balloon-borne hard X-ray/soft Gamma-Ray Polarimeter PoGOLite
- 2007
-
Ingår i: Nuclear Science Symposium Conference Record, 2007. NSS ’07. IEEE. - : IEEE. - 9781424409228 ; , s. 2538-2544
-
Konferensbidrag (refereegranskat)abstract
- The Polarized Gamma-ray Observer - Lightweight version (PoGOLite) is a new balloon experiment capable of detecting 10% polarization from a 200 mCrab source in the 25-80 keV energy range in a single 6-hour flight for the first time. Polarization measurements of hard X-rays and soft gamma-rays are expected to provide a powerful probe into high-energy emission mechanisms as well as source geometries. PoGOLite uses Compton scattering and photo-absorption to measure polarization in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators. The adoption of a well-type phoswich counter concept and a thick polyethylene neutron shield provides a narrow field-of-view (1.25 msr), a large effective area ( gt; 250 cm2 at 40-50 keV), a high modulation factor (more than 25%) and the low background ( 100 mCrab) required to conduct high-sensitivity polarization measurements. Through tests in laboratories and accelerator facilities of a scaled-down prototype with the front-end electronics of flight design and an extensive study by Monte Carlo simulation, we have demonstrated high instrument performance. PoGOLite will be ready for a first engineering flight in 2009 and a science flight in 2010, during which polarization signals from the Crab Nebula/pulsar, Cygnus X-1 and other objects will be observed.
|
|
| 4. |
- Pearce, Mark, et al.
(författare)
-
PoGOLite : A balloon-borne soft gamma-ray polarimeter
- 2007
-
Ingår i: Proceedings of the 30th International Cosmic Ray Conference, ICRC 2007. - : Universidad Nacional Autonoma de Mexico. ; , s. 479-482
-
Konferensbidrag (refereegranskat)abstract
- Polarized gamma-rays are expected from a wide variety of sources including rotationpowered pulsars, accreting black holes and neutron stars, and jet-dominated active galaxies. Polarization measurements provide a powerful probe of the gamma-ray emission mechanism and the distribution of magnetic and radiation fields around the source. No measurements have been performed in the soft gamma-ray band where non-thermal processes are expected to produce high degrees of polarization. The PoGOLite experiment applies well-type phoswich detector technology to polarization measurements in the 25 - 80 keV energy range. The instrument uses Compton scattering and photoabsorption in an array of 217 phoswich detector cells made of plastic and BGO scintillators, and surrounded by active BGO shields. A prototype of the flight instrument has been tested with polarized gammarays and background generated with radioactive sources. The test results and computer simulations confirm that the instrument can detect 10% polarization of a 200 mCrab source in one 6 hour balloon observation. In flight, targets are constrained to within better than 5% of the field-of-view (~5 degrees squared) in order to maximize the effective detection area during observations. The pointing direction on the sky is determined by an attitude control system comprising star trackers, differential GPS receiver system, gyroscopes, accelerometers and magnetometers which provide correction signals to a reaction wheel and torque motor system. Additionally, the entire polarimeter assembly rotates around its viewing axis to minimize systematic bias during observations. Flights are foreseen to start in 2009- 2010 and will target northern sky sources including the Crab pulsar/nebula, Cygnus X-1, and Hercules X-1. These observations will provide valuable information about the pulsar emission mechanism, the geometry around the black hole, and photon transportation in the strongly magnetized neutron star surface, respectively. Future goals include a long duration balloon flight from the Esrange facility in Northern Sweden to Canada.
|
|
| 5. |
- Axelsson, Magnus, et al.
(författare)
-
Measuring energy dependent polarization in soft gamma-rays using compton scattering in PoGOLite
- 2007
-
Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 28:3, s. 327-337
-
Tidskriftsartikel (refereegranskat)abstract
- Linear polarization in X-and gamma-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.
|
|
| 6. |
- Iyudin, A. F., et al.
(författare)
-
GRB redshifts from prompt emission SEDs
- 2007
-
Ingår i: Gamma-Ray Bursts. - : American Institute of Physics (AIP). - 0735404135 - 9780735404137 ; , s. 89-98
-
Konferensbidrag (refereegranskat)abstract
- Recently the very first detection of γ-ray resonant absorptions along the line of sight toward γ-ray bright quasars (QSOs), like 3C273, 3C279, PKS0528+0134 and BL Lacertae were reported. These detections resulted from the analysis of absorption troughs in SEDs derived on the base of mostly EGRET data that were collected during monitoring campaigns of the Virgo and galactic anticenter regions by the Compton Gamma Ray Observatory (CGRO), as well as during ToO observations of QSOs flares. Among three resonant absorption mechanisms that affect the γ-ray spectrum of point-like sources we point out the Δ-isobar resonance that has a very stable peak-energy of the absorption cross-section for all elements (nuclei), and for individual nucleons. By fitting the SED of γ-ray bright point-sources with a high-energy component, including long duration gamma-ray bursts (GRBs), two absorbers can be detected on the sight lines towards such a γ-ray bright point-source. One of those absorbers is at the GRB rest frame, and, therefore, the value of the GRB redshift can be found by fitting an appropriate trough in the SED. A distinct component of GRBs due to the synchrotron self-Compton (SSC) process is expected to be responsible for the significant GRB emission at GeV and TeV energies. Derishev, Aharonian and Kocharovsky suggested that this GeV-TeV emission is observable over a much broader range of angles relative to the direction of the GRB jet. Such GeV-TeV emission will have much harder spectrum and a much higher cut-off frequency compared to the values derived from the Doppler boosting considerations. These factors boost also our expectations for using GRB prompt emission to derive the redshift of host galaxy. Below we discuss a potential application of the gamma-ray absorption method (GRAM) for derivation of the redshift distribution of the long GRBs having a high-energy component, like GRB910503, GRB930131, GRB930506, GRB941017, and GRB980923. Successful application of this method will dramatically broaden the scope of cosmological studies with the use of GRBs.
|
|
| 7. |
- Larsson, S., et al.
(författare)
-
Studies of auroral X-ray backgrounds for high latitude balloon astrophysical experiments
- 2007
-
Ingår i: 18th ESA Symposium on European Rocket and Balloon Programmes and Related Research. - : European Space Agency. ; , s. 513-516
-
Konferensbidrag (refereegranskat)abstract
- Auroral X-ray emission was discovered in the 1950s and has been studied with instruments on balloons, rockets and satellites. While this radiation is of prime interest for studies of space plasma in the Earth's magnetosphere the same radiation is also a background for astrophysical observations made during balloon flights at high latitudes. For such observations it is necessary to monitor and understand the properties of this radiation. This is particularly true for hard X-ray polarimetry which is still an observationally unexplored field. Instruments to measure X-ray polarizations are being developed and will probably first be flown on balloons. We discuss how the auroral X-ray emission and in particular its polarization properties may affect these observations and whether these instruments also can provide information about the high energy electrons producing the X-ray aurora. Optical monitoring of the auroral emissions to allow unambiguous relation of X-ray background to aurora is also discussed.
|
|
