X-ray polarization measurements can provide unique information that is complementary to that obtained through spectroscopic or imaging observations. However, there have been few cases where significant x-ray polarization has been observed. XL-Calibur, conducted in collaboration between Japan, the United States of America, and Sweden, is a balloon-borne mission that aims to conduct high-sensitivity polarimetric observations in the hard x-ray band from 15 to 80 keV. The Japanese group is in charge of developing the Hard X-ray Telescope (HXT) with high light-gathering power. Optical adjustments were completed in 2020, and the performance of the HXT was measured in June 2021 at the SPring-8 (synchrotron radiation facility in Hyogo, Japan). Subsequently, in July 2022, the first observation was conducted from Sweden to Canada. After the flight, the HXT was recovered, and we measured its performance again. By comparing the HXT performances before and after the flight, we found no significant changes that can affect the second flight scheduled in 2024.
The Imaging X-ray Polarimetry Explorer (IXPE) is the unprecedented satellite capable of obtaining the x-ray polarization map. To obtain the accurate polarization map for extended sources, the measurements of the Encircled Energy Function (EEF) in flight is necessary. Though it has been often carried out using point-like source, the background may affect the accurate measurements. So, we have investigated the EEF using the data of the Crab pulsar with the nebula, because the background can be accurately removed by subtracting the off-pulse component from the on-pulse component. With the method, we succeeded in obtaining the energy dependence of the EEF.
IXPE, the first observatory dedicated to imaging x-ray polarimetry, was launched on Dec 9, 2021 and is operating successfully. A partnership between NASA and the Italian Space Agencey (ASI) IXPE features three x-ray telescopes each comprised of a mirror module assembly with a polarization sensitive detector at its focus. An extending boom was deployed on orbit to provide the necessary 4 m focal length. A three-axis-stabilized spacecraft provides power, attitude determination and control, and commanding. After one year of observation IXPE has measured statistically significant polarization from almost all the classes of celestial sources that emit X-rays. In the following we describe the IXPE mission, reporting on its performance after 1.5 year of operations. We show the main astrophysical results which are outstanding for a SMEX mission.
XL-Calibur is a balloon-borne mission for hard x-ray polarimetry. The first launch is currently scheduled from Sweden in summer 2022. Japanese collaborators provide a hard x-ray telescope to the mission. The telescope’s design is identical to the Hard X-ray Telescope (HXT, conically-approximated Wolter-I optics) on board ASTROH with the same focal length of 12 m and the aperture of 45 cm, which can focus x-rays up to 80 keV. The telescope is divided into three segments in the circumferential direction, and confocal 213 grazing-incidence mirrors are precisely placed in the primary and secondary sections of each segment. The surfaces of the mirrors are coated with Pt/C depth-graded multilayer to reflect hard x-rays efficiently by the Bragg reflection. To achieve the best focus, optical adjustment of all of the segments was performed at the SPring-8/BL20B2 synchrotron radiation facility during 2020. A final performance evaluation was conducted in June 2021 and the experiment yields the effective area of 175 cm2 and 73 cm2 at 30 keV and 50 keV, respectively, with its half-power diameter of the point spread function as 2.1 arcmin. The field of view, defined as the full width of the half-maximum of the vignetting curve, is 5.9 arcmin.
HiZ-GUNDAM is a candidate of future satellite mission for the Japanese competitive M-class mission by ISAS/JAXA to progress a time-domain astronomy and multi-messenger astronomy with gamma-ray burst (GRB) phenomena. The science goals are (1) to probe the early universe with high redshift GRBs at z > 7, and (2) to promote the gravitational wave astronomy with short GRB. HiZ-GUNDAM has been successfully passed a review for pre-project candidate in November 2021, and its team is working on the concept study. We will introduce the sciences and mission overview of HiZ-GUNDAM.
Launched on 2021 December 9, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer Mission in collaboration with the Italian Space Agency (ASI). The mission will open a new window of investigation—imaging x-ray polarimetry. The observatory features three identical telescopes, each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at the focus. A coilable boom, deployed on orbit, provides the necessary 4-m focal length. The observatory utilizes a three-axis-stabilized spacecraft, which provides services such as power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets.
Scheduled to launch in late 2021 the Imaging X-ray Polarimetry Explorer (IXPE) is a Small Explorer Mission designed to open up a new window of investigation -- X-ray polarimetry. The IXPE observatory features 3 identical telescope each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at its focus. An extending beam, deployed on orbit provides the necessary 4 m focal length. The payload sits atop a 3-axis stabilized spacecraft which among other things provides power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets. IXPE is a partnership between NASA and the Italian Space Agency (ASI).
This paper introduces a second-generation balloon-borne hard X-ray polarimetry mission, XL-Calibur. X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as pulsars and binary black hole systems. The XL-Calibur contains a grazing incidence X-ray telescope with a focal plane detector unit that is sensitive to linear polarization. The telescope is very similar in design to the ASTRO-H HXT telescopes that has the world’s largest effective area above ~10 keV. The detector unit combines a low atomic number Compton scatterer with a CdZnTe detector assembly to measure the polarization making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. It also contains a CdZnTe imager at the bottom. The detector assembly is surrounded by the improved anti-coincidence shielding, giving a better sensitivity. The pointing system with arcsecond accuracy will be achieved.
XL-Calibur is a balloon-borne hard X-ray polarimetry mission, the first flight of which is currently foreseen for 2021. XL-Calibur carries an X-ray telescope consists of consists of 213 Wolter I grazing-incidence mirrors which are nested in a coaxial and cofocal configuration. The optics design is nearly identical to the Hard X-ray Telescope (HXT) on board the ASTRO-H satellite. The telescope was originally fabricated for the Formation Flying Astronomical Survey Telescope (FFAST) project. However, the telescope can be used for XL-Calibur, since the FFAST project was terminated before completion. The mirror surfaces are coated with Pt/C depth-graded multilayers to reflect hard X-rays above 10 keV by Bragg reflection. The effective area of the telescope is larger than 300 cm^2 at 30 keV. The mirrors are supported by alignment bars in the housing, and each of the bars has a series of 213 grooves to hold the mirrors. To obtain the best focus of the optics, the positions of the mirrors have to be adjusted by tuning the positions of the alignment bars. The tuning of the mirror positions is conducted using the X-ray beam at the synchrotron facility SPring-8 BL20B2, and this process is called optical tuning. First the positions of the second reflectors are tuned, and then those of the first reflectors are tuned. We did the first optical tuning in Jan 2020. The second tuning will be planned between April to July, 2020. This paper reports the current status of the hard X-ray telescope for XL-Calibur.
HiZ-GUNDAM is a future satellite mission which will lead the time-domain astronomy and the multi-messenger astronomy through observations of high-energy transient phenomena. A mission concept of HiZ-GUNDAM was approved by ISAS/JAXA, and it is one of the future satellite candidates of JAXA’s medium-class mission. We are in pre-phase A (before pre-project) and elaborating the mission concept, mission/system requirements for the launch in the late 2020s. The main themes of HiZ-GUNDAM mission are (1) exploration of the early universe with high-redshift gamma-ray bursts, and (2) contribution to the multi-messenger astronomy. HiZ-GUNDAM has two kinds of mission payload. The wide field X-ray monitors consist of Lobster Eye optics array and focal imaging sensor, and monitor ~1 steradian field of view in 0.5 – 4 keV energy range. The near infrared telescope has an aperture size 30 cm in diameter, and simultaneously observes four wavelength bands between 0.5 – 2.5 μm. In this paper, we introduce the mission overview of HiZ-GUNDAM.
The Cherenkov Telescope Array1 (CTA) is the next-generation ground-based observatory for very-high-energy gamma rays. The CTA consists of three types of telescopes with different mirror areas to cover a wide energy range (20 GeV–300 TeV) with an order of magnitude higher sensitivity than the predecessors. Among those telescopes, the Large-Sized Telescope (LST) is designed to detect low-energy gamma rays between 20 GeV and a few TeV with a 23 m diameter mirror. To make the most of such a large light collection area (about 400 m2), the focal plane camera must detect as much reflected Cherenkov light as possible. We have developed each camera component to meet the CTA performance requirements for more than ten years and performed quality-control tests before installing the camera to the telescope.2, 3 The first LST (LST-1) was inaugurated in October 2018 in La Palma, Spain (Figure 1).4 After the inauguration, various calibration tests were performed to adjust hardware parameters and verify the camera performance. In parallel, we have been developing the analysis software to extract physical parameters from low-level data, taking into account some intrinsic characteristics of the switched capacitor arrays, Domino Ring Sampler version 4 (DRS4), used for sampling the waveform of a Cherenkov signal. In this contribution, we describe the hard- ware design of the LST camera in Section 2, a procedure for low-level calibration in Section 3, and the readout e of the LST camera after the hardware calibration with a dedicated analysis chain in Section 4.
The Imaging X-ray Polarimetry Explorer (IXPE) will add polarization to the properties (time, energy, and position) observed in x-ray astronomy. A NASA Astrophysics Small Explorer (SMEX) in partnership with the Italian Space Agency (ASI), IXPE will measure the 2–8-keV polarization of a few dozen sources during the first 2 years following its 2021 launch. The IXPE Observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazingincidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU), separated by a deployable optical bench. The Observatory’s Spacecraft provides typical subsystems (mechanical, structural, thermal, power, electrical, telecommunications, etc.), an attitude determination and control subsystem for 3-axis stabilized pointing, and a command and data handling subsystem communicating with the science instrument and the Spacecraft subsystems.
The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazing-incidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU). The optical bench separating the MMAs from the DUs is a deployable boom with a tip/tilt/rotation stage for DU-to-MMA (gang) alignment, similar to the configuration used for the NuSTAR observatory. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, over the first two years of the mission. For several bright, extended x-ray sources (pulsar wind nebulae, supernova remnants, and an active-galaxy jet), IXPE observations will produce polarization maps indicating the magnetic structure of the synchrotron emitting regions. For many bright pulsating x-ray sources (isolated pulsars, accreting x-ray pulsars, and magnetars), IXPE observations will produce phase-resolved profiles of the polarization degree and position angle.
Hard X-ray imaging polarimeters are developed for the X-ray γ-ray polaeimtery satellite PolariS. The imaging polarimter is scattering type, in which anisotropy in the direction of Compton scattering is employed to measure the hard X-ray (10-80 keV) polarization, and is installed on the focal planes of hard X-ray telescopes. We have updated the design of the model so as to cover larger solid angles of scattering direction. We also examine the event selection algorithm to optimize the detection efficiency of recoiled electrons in plastic scintillators. We succeed in improving the efficiency by factor of about 3-4 from the previous algorithm and criteria for 18-30 keV incidence. For 23 keV X-ray incidence, the recoiled electron energy is about 1 keV. We measured the efficiency to detect recoiled electrons in this case, and found about half of the theoretical limit. The improvement in this efficiency directly leads to that in the detection efficiency. In other words, however, there is still a room for improvement. We examine various process in the detector, and estimate the major loss is primarily that of scintillation light in a plastic scintillator pillar with a very small cross section (2.68mm squared) and a long length (40mm). Nevertheless, the current model provides the MDP of 6% for 10mCrab sources, which are the targets of PolariS.
Y. Inome, G. Ambrosi, Y. Awane, H. Baba, A. Bamba, M. Barceló, U. Barres de Almeida, J. Barrio, O. Blanch Bigas, J. Boix, L. Brunetti, E. Carmona, E. Chabanne, M. Chikawa, N. Cho, P. Colin, J. Contreras, J. Cortina, F. Dazzi, A. Deangelis, G. Deleglise, C. Delgado, C. Díaz, F. Dubois, A. Fiasson, D. Fink, N. Fouque, L. Freixas, C. Fruck, A. Gadola, R. García, D. Gascón, N. Geffroy, N. Giglietto, F. Giordano, F. Grañena, S. Gunji, R. Hagiwara, N. Hamer, Y. Hanabata, T. Hassan, K. Hatanaka, T. Haubold, M. Hayashida, R. Hermel, D. Herranz, K. Hirotani, J. Hose, D. Hugh, S. Inoue, Y. Inoue, K. Ioka, C. Jablonski, M. Kagaya, H. Katagiri, J. Kataoka, H. Kellermann, T. Kishimoto, M. Knoetig, K. Kodani, K. Kohri, T. Kojima, Y. Konno, S. Koyama, H. Kubo, J. Kushida, G. Lamanna, T. Le Flour, M. López-Moya, R. López, E. Lorenz, P. Majumdar, A. Manalaysay, M. Mariotti, G. Martínez, M. Martinez, S. Masuda, S. Matsuoka, D. Mazin, U. Menzel, J. Miranda , R. Mirzoyan, I. Monteiro, A. Moralejo, K. Murase, S. Nagataki, T. Nagayoshi, D. Nakajima, T. Nakamori, K. Nishijima, K. Noda, A. Nozato, M. Ogino, Y. Ohira, M. Ohishi, H. Ohoka, A. Okumura, S. Ono, R. Orito, J. Panazol, D. Paneque, R. Paoletti, J. Paredes, G. Pauletta, S. Podkladkin, J. Prast, R. Rando, O. Reimann, M. Ribó, S. Rosier-Lees, K. Saito, T. Saito, Y. Saito, N. Sakaki, R. Sakonaka, A. Sanuy, M. Sawada, V. Scalzotto, S. Schultz, T. Schweizer, T. Shibata, S. Shu, J. Sieiro, V. Stamatescu, S. Steiner, U. Straumann, R. Sugawara, H. Tajima, H. Takami, M. Takahashi, S. Tanaka, M. Tanaka, L. Tejedor, Y. Terada, M. Teshima, Y. Tomono, T. Totani, T. Toyama, Y. Tsubone, Y. Tsuchiya, S. Tsujimoto, H. Ueno, K. Umehara, Y. Umetsu, A. Vollhardt, R. Wagner, H. Wetteskind, T. Yamamoto, R. Yamazaki, A. Yoshida, T. Yoshida, T. Yoshikoshi
The Large Size Telescopes, LSTs, located at the center of the Cherenkov Telescope Array, CTA, will be sensitive
for low energy gamma-rays. The camera on the LST focal plane is optimized to detect low energy events based
on a high photon detection efficiency and high speed electronics. Also the trigger system is designed to detect
low energy showers as much as possible. In addition, the camera is required to work stably without maintenance
in a few tens of years. In this contribution we present the design of the camera for the first LST and the status
of its development and production.
PolariS (Polarimetry Satellite) is a Japanese small satellite mission dedicated to polarimetry of X-ray and γ-ray sources. The primary aim of the mission is to perform hard X-ray (10-80 keV) polarimetry of sources brighter than 10 mCrab. For this purpose, PolariS employs three hard X-ray telescopes and scattering type imaging polarimeters. PolariS will measure the X-ray polarization for tens of sources including extragalactic ones mostly for the first time. The second purpose of the mission is γ-ray polarimetry of transient sources, such as γ-ray bursts (GRBs). Wide field polarimeters based on similar concept as that used in the IKAROS/GAP but with higher sensitivity will be used, and polarization measurement of 10 GRBs per year is expected.
We are now investigating and studying a small satellite mission HiZ-GUNDAM for future observation of gamma-ray bursts (GRBs). The mission concept is to probe “the end of dark ages and the dawn of formation of astronomical objects”, i.e. the physical condition of early universe beyond the redshift z > 7. We will consider two kinds of mission payloads, (1) wide field X-ray imaging detectors for GRB discovery, and (2) a near infrared telescope with 30 cm in diameter to select the high-z GRB candidates effectively. In this paper, we explain some requirements to promote the GRB cosmology based on the past observations, and also introduce the mission concept of HiZ-GUNDAM and basic development of X-ray imaging detectors.
We are developing a gamma-ray burst polarimeter for a small satellite. It is Compton-scattering-type polarimeter which consists of segmented plastic scintillator and segmented GAGG scintillator. The scattering position in the plastic scintillator and the absorption position in the GAGG scintillator for incident hard X rays can be read out by multi-anode photomultipliers and avalanche photodiodes, respectively. The detection efficiency and the modulation factor amount to about 21% and 39% at 60 keV, respectively. The geometrical area for one module is about 300 cm2. If two modules will be installed, the polarimeters will measure the polarization for about thirty-five GRBs in two years. Through the observation of the polarization, the radiation mechanism of gamma-ray bursts will be clarified.
G. Ambrosi, Y. Awane, H. Baba, A. Bamba, M. Barceló, U. Barres de Almeida, J. Barrio, O. Blanch Bigas, J. Boix, L. Brunetti, E. Carmona, E. Chabanne, M. Chikawa, R. Colin, J. Cortina, J. Contreras, F. Dazzi, A. De Angelis, G. Deleglise, C. Delgado, C. Díaz, A. Fiasson, D. Fink, N. Fouque, L. Freixas, C. Fruck, A. Gadola, R. García, D. Gascon, N. Geffroy, N. Giglietto, F. Giordano, F. Grañena, S. Gunji, R. Hagiwara, N. Hamer, Y. Hanabata, T. Hassan, K. Hatanaka, K. Hirotani, S. Inoue, Y. Inoue, K. Ioka, C. Jablonski, M. Kagaya, H. Katagiri, T. Kishimoto, K. Kodani, K. Kohri, Y. Konno, S. Koyama, H. Kubo, J. Kushida, G. Lamanna, T. Le Flour, E. Lorenz, R. López, M. López-Moya, P. Majumdar, A. Manalaysay, M. Mariotti, G. Martínez, M. Martínez, D. Mazin, J. Miranda , R. Mirzoyan, I. Monteiro, A. Moralejo, K. Murase, S. Nagataki, D. Nakajima, T. Nakamori, K. Nishijima, K. Noda, A. Nozato, Y. Ohira, M. Ohishi, H. Ohoka, A. Okumura, R. Orito, J. Panazol, D. Paneque, R. Paoletti, J. Paredes, G. Pauletta, S. Podkladkin, J. Prast, R. Rando, O. Reimann, M. Ribó, S. Rosier-Lees, K. Saito, T. Saito, Y. Saito, N. Sakaki, R. Sakonaka, A. Sanuy, H. Sasaki, M. Sawada, V. Scalzotto, S. Schultz, T. Schweizer, T. Shibata, S. Shu, J. Sieiro, V. Stamatescu, S. Steiner, U. Straumann, R. Sugawara, H. Tajima, H. Takami, S. Tanaka, M. Tanaka, L. Tejedor, Y. Terada, M. Teshima, T. Totani, H. Ueno, K. Umehara, A. Vollhardt, R. Wagner, H. Wetteskind, T. Yamamoto, R. Yamazaki, A. Yoshida, T. Yoshida, T. Yoshikoshi
The Cherenkov Telescope Array (CTA) project aims to implement the world’s largest next generation of Very High Energy gamma-ray Imaging Atmospheric Cherenkov Telescopes devoted to the observation from a few tens of GeV to more than 100 TeV. To view the whole sky, two CTA sites are foreseen, one for each hemisphere. The sensitivity at the lowest energy range will be dominated by four Large Size Telescopes, LSTs, located at the center of each array and designed to achieve observations of high red-shift objects with the threshold energy of 20 GeV. The LST is optimized also for transient low energy sources, such as Gamma Ray Bursts (GRB), which require fast repositioning of the telescope. The overall design and the development status of the first LST telescope will be discussed.
PolariS (Polarimetry Satellite) is a Japanese small satellite mission dedicated to polarimetry of X-ray and γ-ray sources. The primary aim of the mission is to perform wide band X-ray (4-80 keV) polarimetry of sources brighter than 10 mCrab. For this purpose, Polaris employs three hard X-ray telescopes and two types of focal plane imaging polarimeters. PolariS observations will measure the X-ray polarization for tens of sources including extragalactic ones mostly for the first time. The second purpose of the mission is γ-ray polarimetry of transient sources, such as γ-ray bursts. Wide field polarimeters based on similar concept as that used in the IKAROS/GAP but with higher sensitivity, i.e., polarization measurement of 10 bursts per year, will be employed.
We have been developing a hard X-ray polarimeter to open a new window for hard X-ray astronomy. The project is
called as PHENEX (Polarimetry for High ENErgy X rays). The PHENEX detector is Compton scattering type
polarimeter and it is constructed by several unit counters. The unit counter can achieve the modulation factor and the
detection efficiency of 53% and 20% at 80 keV, respectively. Installing four unit counters, we have carried out balloon-borne
experiment in Jun.13 2006 to preliminarily observe the polarization of the Crab Nebula in hard X-ray band. The
PHENEX polarimeter successfully operated on the level flight and observed the Crab Nebula for about one hour. From
the analysis of the obtained data, it was recognized that the PHENEX polarimeter does not make much spurious
modulation and that the ratio of the signal from the Crab Nebula to the background from the blank sky is 1:3. Though we
can not precisely determine the degree and the direction of the polarization for the Crab Nebula because of the trouble of
the attitude control system, the obtained results were not inconsistent with those in the X-ray band. We will carry out
balloon-borne experiment again, fixing the trouble of the attitude control system.
The solar powered sail spacecraft using a huge sail is a next Japanese engineering verification satellite planned to launch in 2012. It has a hybrid propulsion system with ion engines and a huge solar sail panel of 50 m in diameter. Based on the present mission plan, it will take about 6 years to cruise to Jupiter via Earth swing-bys and 5 more years to reach the Jovian L4 Trojan asteroids. During its cruising phase, we plan to mount a gamma-ray burst (GRB) detector with polarization detection capability which also works as one of the interplanetary network (IPN) to determine the GRB positions. The emission mechanism of GRB is thought to be the synchrotron radiation from the relativistic outflows. If the emission mechanism of GRBs is really synchrotron radiation, the emitted gamma-rays should be strongly polarized. The detection principle is the anisotropy of the Compton scattering. The Compton-scattered gamma-ray photons show the strongly biased distribution toward the vertical direction against the oscillating electric field vector. The design concept of our detector is simple but carefully
avoid a fake modulation. The plastic scintillator in one Compton-length as the scattering body is placed at the center, and 12 CsI scintillators are allocated around it. To avoid a fake modulation through the satellite body scattering, these detectors work in coincidence mode. The coincidence also helps to reduce the particle background. We will use the VA-TA ASIC and FPGA as the analog readout and the digital event processing, respectively, to make the detector weight of almost 2.0 kg. In this paper, we introduce the solar sail mission and show the overview of gamma-ray polarimeter.
The Polarized Gamma-ray Observer (PoGO) is a new balloon-borne instrument designed to measure polarization from astrophysical objects in the 30-200 keV range. It is under development for the first flight anticipated in 2008. PoGO is designed to minimize the background by an improved phoswich configuration, which enables a detection of 10 % polarization in a 100 mCrab source in a 6--8 hour observation. To achieve such high sensitivity, low energy response of the detector is important because the source count rate is generally dominated by the lowest energy photons. We have developed new PMT assemblies specifically designed for PoGO to read-out weak scintillation light of one photoelectron (1 p.e.) level. A beam test of a prototype detector array was conducted at the KEK Photon Factory, Tsukuba in Japan. The experimental data confirm that PoGO can detect polarization of 80-85 % polarized beam down to 30 keV with a modulation factor 0.25 ± 0.05.
We make a plan of a hard X-ray polarimetry experiment with a small satellite. Bright point-like sources in 20-80keV are prime targets, for which we will not use focusing optics. Comparing various types of polarimeters, we adopt a scattering type in which anisotropy in scattering directions of photons is employed. After optimization of the design is considered with simplified models of scattering polarimeters, we propose to use segmented scatter targets made of plastic scintillators, with which scattering location is identified by detecting recoiled electrons. Simulations show that recoiled electrons are detectable when incident X-ray energies are above 40keV, for which higher polarimetry sensitivity is obtained. We confirmed the performance of such a polarimeter in experiments at a Synchrotron facility and performed a balloon flight in which a proto type unit of the polarimeter was onboard. We finally discuss feasibility of a small satellite experiment in which many of the polarimeter units will be employed. Twenty five units of the polarimeter enable us to detect hard X-ray polarization of 5-10% for a hundred mCrab sources. Improvement in the sensitivity to detect recoiled electrons will significantly improve the polarimetry sensitivity. We also consider a low energy extension of our system down to below 10keV in order to cover wide energy range.
We constructed an optical imaging x-ray detector with a capillary gas proportional counter (CGPC), a focusing mirror system, and an image intensified CCD camera. The CGPC consists of an absorption region for x-rays, which also operates as a drift region of electron clouds, and a gas proportional scintillation region in a capillary plate. With a gas mixture of Xe plus 2% CH4 at 1 atm and a gas gain 8000, the light output from the CGPC is several tens thousand times larger than that of a typical NaI(Tl) scintillator and it is enough to image electron clouds due to a few tens keV x rays. To investigate the imaging ability, images for tracks due to (alpha) particles (241Am) of 5.5 MeV were taken in the gas mixture of Xe plus CH4, for the several reduced fields in the drift region. We confirmed that the images were most clearly observed at around the reduced fields of 40 V/cm(DOT)atm.
The ASTRO-E satellite is scheduled for launch in 2000 by the Institute of Space and Astronautical Science (ISAS). In this paper the design and performance of the hard x ray detector (HXD) developed for ASTRO-E are described. The HXD is a combination of YAP/BGO phoswich scintillators and silicon PIN diodes covering a wide energy band of 10 - 700 keV. The detector background is reduced down to several times 10-6c/s/cm2/keV, and the sensitivity of the HXD is more than one order of magnitude higher than any other past missions in the range of a few 10 keV to several 100 keV. Thus ASTRO-E HXD is expected to achieve an extreme high performance for detecting cosmic hard x rays and low-energy gamma rays. Astrophysics to be explored with the HXT are expected to be extremely widespread and rich.
The fourth Japanese x-ray astronomy satellite, ASCA, carries two imaging gas scintillation proportional counters (GIS) on its focal plane. Extensive ground calibration has established its position resolution to be 0.5 mm and FWHM energy resolution to be 8.0% both at 6 keV. When combined with the x-ray telescope, a sensitivity range becomes 0.7 - 10 keV. These properties have been confirmed through in-orbit calibrations. The in-orbit background of the GIS has been confirmed to be as low as (5 - 7) X 10-4 c s-1cm-2keV-1 over the 1 - 10 keV range. The long-term detector gain is stable within a few % for two years. Gain dependence on the position and temperature has been calibrated down to 1%. The overall energy response is calibrated very accurately. Thus the GIS is working as an all-round cosmic x-ray detector.
We designed a new type of polarimeter for polarized hard x rays from stellar objects, utilizing the principle that the direction of the Compton scattered x rays depends on the electric vector of the polarized incident x rays. The characteristics of the new designed polarimeter were investigated by measurements of basic data and computer simulations. From them, it is shown that the polarimeter is capable of observing the interesting astrophysical objects by using a balloon or a satellite. In this paper, we report the characteristics and the expected performance of the new designed hard x-ray polarimeter.
We have developed a low background hard X-ray/gamma-ray telescope for balloon-borne experiments. The telescope called Welcome-1 (Well type Compound Eye) utilizes newly developed well-type phoswich counters. In the well-type phoswich counter, the background from external and internal sources are reduced significantly, Welcome-1 is designed for observation in the energy range from 60 keV to 800-1000 keV. The effective area of Welcome-1 is 740 sq cm at 122 keV and 222 sq cm at 511 keV line. We flew Welcome-1 in 1990 and 1991 to detect hard X-rays from SN1987A, PSR1509-58, Cen-A and others. The background levels at an altitude of 4g/sq cm are 1 x 10 exp -4/sq cm photons/s/keV at 122 keV and 3 x 10 exp -5 photons/sq cm/s/keV at 511 keV. The data obtained during the flight shows that the detector in fact has the 3 sigma sensitivity of about a few x 10 exp -6 photons/sq cm/s/keV and about 10 exp -4 photons/sq cm/s in a 10 exp 4 s observation for the continuum spectrum and line spectrum, respectively.
We have developed a new kind of phoswich counters that are capable of detecting low flux hard X-ray/γ-ray from localized sources. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The well-shaped shielding part acts as an active collimator as well as an active shield. The whole assembly is viewed by a phototube from the exterior bottom surface of the shielding part. By using an appropriate pulse-shape discriminator (PSD), hard X-rays/gamma-rays that have deposited energy only in the detection part can be selected.
The first counter was built by using a new scintillator (GSO) for the detection part and CsI(Tt) for the shielding part. A detector system consisting of 64 such phoswich counters (total area ~740cm2) was flown three times on board a balloon,
setting a limit to the 57Co line flux from SN1987A at around 10-4cm-2s, determining the pulsating hard X/γ-ray flux of PSR15O9-58, determining the hard X/γ-ray spectra of CenA and GX339-04.
Analyses have revealed the fact that background counts due to the Compton scattering, nuclear reactions, and β-γ radioactivities in the detector are largely suppressed because they are likely to register at least one extra count in the shielding part. The ultimate sensitivity of the detector will then be determined by the level of radioactive contamination.
Other scintillator combinations such as GSO/BGO, NaI(Tl)/CsI(Tl), and YAIO3/BGO have also been studied. Efforts
to reduce the radioactive contamination in scintillators have also been actively pursued. In near future we expect to reach a sensitivity (3σ) around a few times 10-7cm-2s-1keV-1 for continuum in a 104s balloon observation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.