The HiZ-GUNDAM mission is one of the candidates for the JAXA’s competitive M-class missions. HiZ-GUNDAM revolutionizes our understanding of the high redshift universe and promotes multi-messenger astronomy. Combining a highly sensitive wide-field X-ray monitor, a near-infrared telescope, and autonomous spacecraft slew capability makes a powerful machine to hunt interesting X-ray transients and immediately identify their counterparts in near-infrared. The Wide Field X-ray Monitor (WFXM) is the main instrument to search for the transients in the soft X-ray band. WFXM comprises lobster-eye optics (LEO) and pnCCD as an X-ray imager. LEO has a size of 40 mm x 40 mm and a radius of curvature of 600 mm. We are planning to use the LEO manufactured by Photonis Inc. One WFXM module has three by three LEOs, which cover a field of view of 12 deg x 12 deg. The current baseline design is composed of 16 modules to cover 0.7 sr sky. The candidate focal imager is the pnCCD detector by PNSensor Inc. We will present the current status and prospects of the WFXM.
KEYWORDS: X-rays, Analog electronics, Power supplies, Analog to digital converters, Field programmable gate arrays, X-ray imaging, X-ray detectors, Gamma radiation, Optical sensors
HiZ-GUNDAM is a candidate satellite mission for JAXA to promote time-domain and multi-messenger astronomy as the main targets of gamma-ray bursts. As the mission payload, one of the module of the wide field X-ray monitors consist of a lobster eye optics array and a focal imaging sensor. The field of view of the monitor covers ∼ 0.7 steradian of the sky in the soft X-ray band (0.4 − 4 keV). As the X-ray detector, the pnCCD detector fabricated by PNSensor Inc. can achieve our mission requirements. And we are developing an FPGA-based electronic system for the pnCCD.Our bread-board model of the electronic system consists of (1) a FPGA board, (2) an ADC and power supply board, (3) a pnCCD mounting board, and (4) a 96 × 192-pixel pnCCD read out by 4 CAMEX analog front-end ASICs. We have driven the front-end electronics of the pnCCD successfully by sending the test pulse. In this paper, we report the development status of our FPGA-based electronic system to control the pnCCD sensor.
We are developing a wide-field X-ray monitor onboard the HiZ-GUNDAM mission. HiZ-GUNDAM is a future satellite mission for gamma-ray burst observation to lead the time domain astronomy and multi-messenger astronomy. The pnCCD detectors will be used as a focal plane detector, which is a back-illuminated CCD and fully depleted by reverse-biased pn-junctions on front and back sides. It has a high sensitivity to low-energy X-rays and achieves a high frame rate with column-parallel readout. It was originally developed for X-ray astronomy, and its high radiation hardness has been verified on satellites such as the XMM-Newton and the eRosita mission. The detector temperature is assumed to be around −20 °C, which is higher than that of usual space use CCD sensors, due to thermal design constraints.
We investigated the spectral performance of pnCCDs using a small-sized device mounted on the camera system manufactured by PNDetector GmbH. Several fluorescence X-ray lines from 0.28 keV(C-Kα) to 4.5keV (Ti-Kα) were used for measurements. The energy resolution of 52 eV for 0.28 keV was verified, with a frame rate of 100 Hz at −20 °C of operating temperature. We also made measurements of dark current for various temperatures ranging from −20 to 0 °C and evaluated that the lower discriminated energy could be 123 eV even at 0 °C. These results verified to satisfy the mission requirements of HiZ-GUNDAM.
HiZ-GUNDAM is a future satellite mission whose mission concept was approved by ISAS/JAXA, and it is one of the future satellite candidates of JAXA’s competitive medium-class mission. HiZ-GUNDAM will lead time-domain astronomy in 2030s, and its key sciences are (1) exploration of the early universe with high-redshift gamma-ray bursts, and (2) contribution to the multi-messenger astronomy. Two mission payloads are aboard HiZ-GUNDAM to realize these two scientific issues. The wide field X-ray monitors which consist of Lobster Eye optics array and focal imaging sensor, monitor ~0.5 steradian field of view in 0.5–4 keV energy range. The near infrared telescope with an aperture size of 30 cm in diameter performs simultaneous 5-band photometric observation in 0.5–2.5 μm wavelength with Koester’s prism for X-ray transients discovered by Wide Field X-ray Monitor. In this paper, we introduce the mission overview of HiZ-GUNDAM while the information contained herein may change in future studies.
HiZ-GUNDAM is a future satellite mission designed for exploring the early universe using gamma-ray bursts (GRBs). The satellite is equipped with two main instruments: a wide field X-ray monitor (WFXM) and a near infrared telescope (NIRT). And its mission data processing unit (MPU) plays an important role in data processing. When a transient source occurs and the X-rays enter the WFXM, a cross-shaped image is produced on the focal plane image sensor. Once the WFXM’s data are sent to the MPU, the direction of the source is determined from the center position. Furthermore, if there are no known stellar objects in this direction and if they are not hot pixels or other anomalies, the event is classified as a GRB candidate. To evaluate the software for this series of judgments, we investigated the angular resolution by this software algorithm utilizing the cross image obtained by the lobster eye optics (LEO).
HiZ-GUNDAM is a future satellite mission for gamma-ray burst observations. One of the mission instruments is the wide-field X-ray monitor with a field of view (FoV) of 0.6 steradian at 0.4–4.0 keV, consisting of Lobster Eye Optics (LEO) and pnCCD image sensors. LEOs need to be spatially well-aligned to achieve both of wide FoV and fine position accuracy of < 3 arcmin. To address this challenge, we explored an alignment method with X-rays and developed an optical frame. This study reports on the evaluation of the optical frame, our alignment method, and x-ray performance of the optical system.
HiZ-GUNDAM is a future satellite mission for gamma-ray burst observations. One of the mission instruments is the wide-field X-ray monitor with a field of view (FoV) of 0.5 steradian at 0.4 to 4.0 keV, consisting of Lobster Eye Optics (LEO) and focal-imaging pixel sensors. LEOs need to be spatially well-aligned to achieve both a wide FoV and fine accuracy in determining the location of X-ray transients. An alignment method is being investigated with visible light and shape measurements. We developed a titanium frame for positioning two LEO segments and estimated visible light on LEOs. We will report development of the alignment method.
X-ray observation covering a wide field of view with a good sensitivity is essential to search for an electromagnetic counterpart of gravitational wave events. A lobster-eye optics (LEO) and a large area CMOS sensor are good instruments to achieve this goal. Furthermore, thanks to the light weight of LEO, it is possible to install on a small platform such as a CubeSat. However, real-time identification of x-ray events is challenging to perform in the restricted resources. Therefore, we utilize one of the machine learning models of convolutional neural network (CNN) to extract x-ray events in the image taken from a CMOS sensor. Moreover, we use a Sony micro board computer, Spresense, ultra-low power consumption, and supports machine learning libraries for the process. This presentation will introduce our machine learning-based x-ray event selection process targeting to use for a CubeSat.
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.
We propose an optimized source detection algorithm with an X-ray wide-field imaging detector based on lobstereye (LE) optics to realize better sensitivity. In our method, we take two parts of region of interest (ROI) in which we test the number of X-ray events exceed a certain threshold level. Since we compose the condition that the excesses of the photons are required for the both parts of the ROI, we can lower the detection threshold level with a less false alert rate. We take two comparative methods in which the ROI consists of one part, and compared the performance of them. We formulated an appropriate threshold level and sensitivity for two comparable detection methods as well as our proposed method. We found that the detection sensitivity of our method is improved by a factor of about 30% at most than that of the comparable methods in the nominal case of the proposed HiZ-GUNDAM mission. We also found that which detection method has better sensitivity depends on the background event rate. We checked that the formulation works well by comparing to a Monte Carlo simulation in the case of the HiZ-GUNDAM condition. The formula can be applied to any future missions with LE optics to design which detection algorithm is suitable for optimizing sensitivity.
Lobster eye optics (LEO) is an optics composed of many pores aligned along a sphere. Since the LEO can cover a wide field of view with good sensitivity in soft X-rays, it makes an ideal telescope to search for interesting transient sources such as high redshift gamma-ray bursts, electromagnetic counterparts of gravitational wave sources, and so on. We obtained two LEOs of different specifications manufactured by Photonis inc. (hereafter PLEO) and NNVT inc. (hereafter NLEO) and evaluated their X-ray performance. We confirmed that both LEOs focus parallel X-rays and make an image containing a center spot, cross arms, and scattering components at the focal plane, as suggested by Angel (1979). The full widths at half maximum of the measured point spread functions are ∼ 11′ (PLEO) and ∼ 4 ′ (NLEO). The effective areas of the central component at 1.5 keV are 1.37 cm2 (PLEO) and 2.58 cm2 (NLEO). Based on our developed simulator calibrated using our X-ray measurements, the position accuracy of the PLEO is expected to be less than 1′ if the number of detected photons is more than 500.
In this paper we report on development of an FPGA-based fast readout system of a CMOS image sensor for the future satellite mission HiZ-GUNDAM observing gamma-ray bursts (GRBs) in the 0.4–4 keV band. Since the typical durations of GRBs are about 0.1–100 s, an X-ray photon-counting capability with a time resolution of < 0.1 s is required. The FPGA-based signal processing system has the following functions: (1) take images with a few million pixels at a frame rate of >10 frames per second, (2) extract X-ray events by image subtraction, (3) compile position and energy information of the obtained X-ray events, and (4) transfer the information to an external CPU. A more detailed system configuration is reported.
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.
We propose a concept of multiplexing lobster-eye (MuLE) optics to achieve significant reductions in the number of focal plane imagers in lobster-eye (LE) wide-field x-ray monitors. In the MuLE configuration, an LE mirror is divided into several segments and the x-rays reflected on each of these segments are focused on a single image sensor in a multiplexed configuration. If each LE segment assumes a different rotation angle, the azimuthal rotation angle of a cross-like image reconstructed from a point source by the LE optics identifies the specific segment that focuses the x-rays on the imager. With a focal length of 30 cm and LE segments with areas of 10 × 10 cm2, ∼1 sr of the sky can be covered with 36 LE segments and only four imagers (with total areas of 10 × 10 cm2). A ray tracing simulation was performed to evaluate the nine-segment MuLE configuration. The simulation showed that the flux (0.5 to 2 keV) associated with the 5σ detection limit was ∼2 × 10 − 10 erg cm − 2 s − 1 (10 mCrab) for a transient with a duration of 100 s. The simulation also showed that the direction of the transient for flux in the range of 14 to 17 mCrab at 0.6 keV was determined correctly with a 99.7% confidence limit. We conclude that the MuLE configuration can become an effective on-board device for small satellites for future x-ray wide-field transient monitoring.
M. Feroci, E. Bozzo, S. Brandt, M. Hernanz, M. van der Klis, L.-P. Liu, P. Orleanski, M. Pohl, A. Santangelo, S. Schanne, L. Stella, T. Takahashi, H. Tamura, A. Watts, J. Wilms, S. Zane, S.-N. Zhang, S. Bhattacharyya, I. Agudo, M. Ahangarianabhari, C. Albertus, M. Alford, A. Alpar, D. Altamirano, L. Alvarez, L. Amati, C. Amoros, N. Andersson, A. Antonelli, A. Argan, R. Artigue, B. Artigues, J.-L. Atteia, P. Azzarello, P. Bakala, D. Ballantyne, G. Baldazzi, M. Baldo, S. Balman, M. Barbera, C. van Baren, D. Barret, A. Baykal, M. Begelman, E. Behar, O. Behar, T. Belloni, F. Bernardini, G. Bertuccio, S. Bianchi, A. Bianchini, P. Binko, P. Blay, F. Bocchino, M. Bode, P. Bodin, I. Bombaci, J.-M. Bonnet Bidaud, S. Boutloukos, F. Bouyjou, L. Bradley, J. Braga, M. Briggs, E. Brown, M. Buballa, N. Bucciantini, L. Burderi, M. Burgay, M. Bursa, C. Budtz-Jørgensen, E. Cackett, F. Cadoux, P. Cais, G. Caliandro, R. Campana, S. Campana, X. Cao, F. Capitanio, J. Casares, P. Casella, A. Castro-Tirado, E. Cavazzuti, Y. Cavechi, S. Celestin, P. Cerda-Duran, D. Chakrabarty, N. Chamel, F. Château, C. Chen, Y. Chen, J. Chenevez, M. Chernyakova, J. Coker, R. Cole, A. Collura, M. Coriat, R. Cornelisse, L. Costamante, A. Cros, W. Cui, A. Cumming, G. Cusumano, B. Czerny, A. D'Aì, F. D'Ammando, V. D'Elia, Z. Dai, E. Del Monte, A. De Luca, D. De Martino, J. P. C. Dercksen, M. De Pasquale, A. De Rosa, M. Del Santo, S. Di Cosimo, N. Degenaar, J. W. den Herder, S. Diebold, T. Di Salvo, Y. Dong, I. Donnarumma, V. Doroshenko, G. Doyle, S. Drake, M. Durant, D. Emmanoulopoulos, T. Enoto, M. H. Erkut, P. Esposito, Y. Evangelista, A. Fabian, M. Falanga, Y. Favre, C. Feldman, R. Fender, H. Feng, V. Ferrari, C. Ferrigno, M. Finger, G. Fraser, M. Frericks, M. Fullekrug, F. Fuschino, M. Gabler, D. K. Galloway, J. L. Gálvez Sanchez, P. Gandhi, Z. Gao, E. Garcia-Berro, B. Gendre, O. Gevin, S. Gezari, A. B. Giles, M. Gilfanov, P. Giommi, G. Giovannini, M. Giroletti, E. Gogus, A. Goldwurm, K. Goluchová, D. Götz, L. Gou, C. Gouiffes, P. Grandi, M. Grassi, J. Greiner, V. Grinberg, P. Groot, M. Gschwender, L. Gualtieri, M. Guedel, C. Guidorzi, L. Guy, D. Haas, P. Haensel, M. Hailey, K. Hamuguchi, F. Hansen, D. Hartmann, C. A. Haswell, K. Hebeler, A. Heger, M. Hempel, W. Hermsen, J. Homan, A. Hornstrup, R. Hudec, J. Huovelin, D. Huppenkothen, S. Inam, A. Ingram, J. In't Zand, G. Israel, K. Iwasawa, L. Izzo, H. Jacobs, F. Jetter, T. Johannsen, P. Jenke, P. Jonker, J. Josè, P. Kaaret, K. Kalamkar, E. Kalemci, G. Kanbach, V. Karas, D. Karelin, D. Kataria, L. Keek, T. Kennedy, D. Klochkov, W. Kluzniak, E. Koerding, K. Kokkotas, S. Komossa, S. Korpela, C. Kouveliotou, A. Kowalski, I. Kreykenbohm, L. Kuiper, D. Kunneriath, A. Kurkela, I. Kuvvetli, F. La Franca, C. Labanti, D. Lai, F. Lamb, C. Lachaud, P. Laubert, F. Lebrun, X. Li, E. Liang, O. Limousin, D. Lin, M. Linares, D. Linder, G. Lodato, F. Longo, F. Lu, N. Lund, T. Maccarone, D. Macera, S. Maestre, S. Mahmoodifar, D. Maier, P. Malcovati, J. Malzac, C. Malone, I. Mandel, V. Mangano, A. Manousakis, M. Marelli, J. Margueron, M. Marisaldi, S. Markoff, A. Markowitz, A. Marinucci, A. Martindale, G. Martínez, I. McHardy, G. Medina-Tanco, M. Mehdipour, A. Melatos, M. Mendez, S. Mereghetti, S. Migliari, R. Mignani, M. Michalska, T. Mihara, M. C. Miller, J. M. Miller, T. Mineo, G. Miniutti, S. Morsink, C. Motch, S. Motta, M. Mouchet, G. Mouret, J. Mulačová, F. Muleri, T. Muñoz-Darias, I. Negueruela, J. Neilsen, T. Neubert, A. Norton, M. Nowak, A. Nucita, P. O'Brien, M. Oertel, P. E. H. Olsen, M. Orienti, M. Orio, M. Orlandini, J. Osborne, R. Osten, F. Ozel, L. Pacciani, F. Paerels, S. Paltani, M. Paolillo, I. Papadakis, A. Papitto, Z. Paragi, J. Paredes, A. Patruno, B. Paul, F. Pederiva, E. Perinati, A. Pellizzoni, A. V. Penacchioni, U. Peretz, M. Perez, M. Perez-Torres, B. Peterson, V. Petracek, C. Pittori, J. Pons, J. Portell, A. Possenti, K. Postnov, J. Poutanen, M. Prakash, I. Prandoni, H. Le Provost, D. Psaltis, J. Pye, J. Qu, D. Rambaud, P. Ramon, G. Ramsay, M. Rapisarda, A. Rashevski, I. Rashevskaya, P. Ray, N. Rea, S. Reddy, P. Reig, M. Reina Aranda, R. Remillard, C. Reynolds, L. Rezzolla, M. Ribo, R. de la Rie, A. Riggio, A. Rios, D. Rischke, P. Rodríguez-Gil, J. Rodriguez, R. Rohlfs, P. Romano, E. M. Rossi, A. Rozanska, A. Rousseau, B. Rudak, D. Russell, F. Ryde, L. Sabau-Graziati, T. Sakamoto, G. Sala, R. Salvaterra, D. Salvetti, A. Sanna, J. Sandberg, T. Savolainen, S. Scaringi, J. Schaffner-Bielich, H. Schatz, J. Schee, C. Schmid, M. Serino, N. Shakura, S. Shore, J. Schnittman, R. Schneider, A. Schwenk, A. Schwope, A. Sedrakian, J.-Y. Seyler, A. Shearer, A. Slowikowska, M. Sims, A. Smith, D. Smith, P. Smith, M. Sobolewska, V. Sochora, P. Soffitta, P. Soleri, L. Song, A. Spencer, A. Stamerra, B. Stappers, R. Staubert, A. Steiner, N. Stergioulas, A. Stevens, G. Stratta, T. Strohmayer, Z. Stuchlik, S. Suchy, V. Suleimanov, F. Tamburini, T. Tauris, F. Tavecchio, C. Tenzer, F. Thielemann, A. Tiengo, L. Tolos, F. Tombesi, J. Tomsick, G. Torok, J. M. Torrejon, D. F. Torres, E. Torresi, A. Tramacere, I. Traulsen, A. Trois, R. Turolla, S. Turriziani, S. Typel, P. Uter, P. Uttley, A. Vacchi, P. Varniere, S. Vaughan, S. Vercellone, M. Vietri, F. Vincent, V. Vrba, D. Walton, J. Wang, Z. Wang, S. Watanabe, R. Wawrzaszek, N. Webb, N. Weinberg, H. Wende, P. Wheatley, R. Wijers, R. Wijnands, M. Wille, C. Wilson-Hodge, B. Winter, S. Walk, K. Wood, S. Woosley, X. Wu, R. Xu, W. Yu, F. Yuan, W. Yuan, Y. Yuan, G. Zampa, N. Zampa, L. Zampieri, L. Zdunik, A. Zdziarski, A. Zech, B. Zhang, C. Zhang, S. Zhang, M. Zingale, F. Zwart
The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.
Polarimeters for Energetic Transients (POET) is a mission concept designed to t within the envelope of a NASA Small Explorer (SMEX) mission. POET will use X-ray and gamma-ray polarimetry to uncover the energy release mechanism associated with the formation of stellar-mass black holes and investigate the physics of extreme magnetic ields in the vicinity of compact objects. Two wide-FoV, non-imaging polarimeters will provide polarization measurements over the broad energy range from about 2 keV up to about 500 keV. A Compton scatter polarimeter, using an array of independent scintillation detector elements, will be used to collect data from 50 keV up to 500 keV. At low energies (2{15 keV), data will be provided by a photoelectric polarimeter based on the use of a Time Projection Chamber for photoelectron tracking. During a two-year baseline mission, POET will be able to collect data that will allow us to distinguish between three basic models for the inner jet of gamma-ray bursts.
KEYWORDS: Avalanche photodetectors, X-rays, Field effect transistors, Resistance, Crystals, Sensors, Hard x-rays, Scintillators, Analog electronics, Stanford Linear Collider
WF-MAXI is a mission to detect and localize X-ray transients with short-term variability as gravitational-wave (GW) candidates including gamma-ray bursts, supernovae etc. We are planning on starting observations by WF-MAXI to be ready for the initial operation of the next generation GW telescopes (e.g., KAGRA, Advanced LIGO etc.). WF-MAXI consists of two main instruments, Soft X-ray Large Solid Angle Camera (SLC) and Hard X-ray Monitor (HXM) which totally cover 0.7 keV to 1 MeV band. HXM is a multi-channel array of crystal scintillators coupled with APDs observing photons in the hard X-ray band with an effective area of above 100 cm2. We have developed an analog application specific integrated circuit (ASIC) dedicated for the readout of 32-channel APDs' signals using 0.35 μm CMOS technology based on Open IP project and an analog amplifier was designed to achieve a low-noise readout. The developed ASIC showed a low-noise performance of 2080 e- + 2.3 e-/pF at root mean square and with a reverse-type APD coupled to a Ce:GAGG crystal a good FWHM energy resolution of 6.9% for 662 keV -rays.
WF-MAXI is a soft X-ray transient monitor proposed for the ISS/JEM. Unlike MAXI, it will always cover a large field of view (20 % of the entire sky) to detect short transients more efficiently. In addition to the various transient sources seen by MAXI, we hope to localize X-ray counterparts of gravitational wave events, expected to be directly detected by Advanced-LIGO, Virgo and KAGRA in late 2010's. The main instrument, the Soft X-ray Large Solid Angle Cameras (SLC) is sensitive in the 0.7-12 keV band with a localization accuracy of ~ 0:1°. The Hard X-ray Monitor (HXM) covers the same sky field in the 20 keV-1 MeV band.
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.
Wide-Field MAXI (WF-MAXI) planned to be installed in Japanese Experiment Module “Kibo” Exposed Facility of the international space station (ISS). WF-MAXI consists of two types of cameras, Soft X-ray Large Solid Angle Camera (SLC) and Hard X-ray Monitor (HXM). HXM is multi-channel arrays of CsI scintillators coupled with avalanche photodiodes (APDs) which covers the energy range of 20 - 200 keV. SLC is arrays of CCD, which is evolved version of MAXI/SSC. Instead of slit and collimator in SSC, SLC is equipped with coded mask allowing its field of view to 20% of all sky at any given time, and its location determination accuracy to few arcminutes. In older to achieve larger effective area, the number of CCD chip and the size of each chip will be larger than that of SSC. We are planning to use 59 x 31 mm2 CCD chip provided by Hamamatsu Photonics. Each camera will be quipped with 16 CCDs and total of 4 cameras will be installed in WF-MAXI. Since SLC utilize X-ray CCDs it must equip active cooling system for CCDs. Instead of using the peltier cooler, we use mechanical coolers that are also employed in Astro-H. In this way we can cool the CCDs down to -100C. ISS orbit around the earth in 90 minutes; therefore a point source moves 4 arcminutes per second. In order to achieve location determination accuracy, we need fast readout from CCD. The pulse heights are stacked into a single row along the vertical direction. Charge is transferred continuously, thus the spatial information along the vertical direction is lost and replaced with the precise arrival time information. Currently we are making experimental model of the camera body including the CCD and electronics for the CCDs. In this paper, we show the development status of SLC.
We made one-dimensional detector arrays applying the newly developed Schottky CdTe technique. Two prototypes are manufactured; one consists of eight pixels of 2 x 2 x 0.5 mm3 each (2 mm module) and the other eight pixels of 25 x 2 x 0.5 mm3 each (25 mm module). The single element read-out test of the 2 mm module showed an energy resolution of ~1.7 keV at 59.5 keV, at 0°C for the bias voltage of 400 V. The 25 mm modules showed an energy resolution of ~4.5 keV at 59.5 keV at 0°C for the bias voltage of 300 V. Signals from the four sets of the CdTe modules (32 pixels in total) are read out by the VA/TA chips made by IDE company. The energy resolution of the 2 mm module is ~3.0 keV on average at 59.5 keV at room temperature for the bias voltage of 350 V. The 25 mm modules have an energy resolution of ~6.1 keV on average at 122.1 keV at room temperature for the bias voltage of 300 V. In view of these results, the manufactured arrays are promising as spectroscopic detectors for hard X-rays and γ-rays. A few modifications are needed in the VA/TA chips to be applied for the CdTe X-ray detector. Applications of CdTe detector arrays to a slit or coded-mask camera, and an imaging polarimeter are stated.
The Wide-field X-ray Monitor (WXM) is one of the scientific
instruments carried on the High Energy Transient Explorer 2 (HETE-2)
satellite launched in October 2000. The WXM consists of three elements: (1) four identical Xe-filled one-dimensional position-sensitive proportional counters, two in the spacecraft X-direction and two in the Y-direction, (2) two sets of one-dimensional coded apertures orthogonally mounted above the counters in the X and Y-direction, and (3) the main electronics that processes analog signals from the counters. The WXM counters are sensitive to X-rays between 2 keV and 25 keV within a field-of-view of about 1.5 sr with a total detector area of about 350 cm2. The combination of the apertures and the counters provides GRB locations with accuracy ~10 arcmin. The counters and electronics are developed and fabricated by RIKEN, and the apertures and on-board software are designed and provided by Los Alamos National Laboratory. The WXM plays a major roll in the GRB localization and its spectroscopy in the energy range between 2 keV and 25 keV. During the first year of observations, a number of steady X-ray sources as well as high-energy transients were detected with the WXM. Observing Crab nebula and Sco X-1, we have calibrated the detector alignment between the WXM and the optical camera system with 2 arcmin accuracy. As of 29 July 2002, nineteen GRBs have been localized with the WXM in the 18 months of stable operations. Twelve of them were reported to the GCN within a delay of 10 hours, and 4 optical transients were identified by ground based telescopes. The energy response of the detectors has also been calibrated using the Crab spectrum. We report the in-orbit performance of the WXM instrument during the first 18 months.
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