共查询到20条相似文献，搜索用时 31 毫秒
1.
A. Ong R. D. Bhattacharya C. E. Covault D. D. Dixon D. T. Gregorich D. S. Hanna S. Oser J. Qu bert D. A. Smith O. T. Tü mer A. D. Zych 《Astroparticle Physics》1996,5(3-4):353-365
There is considerable interest world-wide in developing large area atmospheric Cherenkov detectors for ground-based gamma-ray astronomy. This interest stems, in large part, from the fact that the gamma-ray energy region between 20 and 250 GeV is unexplored by any experiment. Atmospheric Cherenkov detectors offer a possible way to explore this region, but large photon collection areas are needed to achieve low energy thresholds. We are developing an experiment using the heliostat mirrors of a solar power plant as the primary collecting element. As part of this development, we built a detector using four heliostat mirrors, a secondary Fresnel lens, and a fast photon detection system. In November 1994, we used this detector to record atmospheric Cherenkov radiation produced by cosmic ray particles showering in the atmosphere. The detected rate of cosmic ray events was consistent with an energy threshold near 1 TeV. The data presented here represent the first detection of atmospheric Cherenkov radiation using solar heliostats viewed from a central tower. 相似文献
2.
Emanuele Perinati Chris Tenzer Andrea Santangelo Konrad Dennerl Michael Freyberg Peter Predehl 《Experimental Astronomy》2012,33(1):39-53
The pn-CCD cameras at the focal plane of the eROSITA space observatory will be the first X-ray (0.2?C12?keV) detector to operate in a L-2 orbit. Therefore, no direct information of instrumental non X-ray background (NXB) is available to make predictions for eROSITA. Since, in general, the instrumental NXB experienced in orbit has a major impact on the overall sensitivity of the cameras, we investigated and modeled the L-2 radiation environment and its interaction with the eROSITA mass distribution and cameras, in order to quantify the expected pn-CCD NXB level. We obtain an average value of NXB ??25% lower than that observed by the pn-CCDs on-board the XMM-Newton satellite, which is placed in a Highly Elliptical Orbit (HEO). We discuss this result in light of the differences between the L-2 and HEO space environments. 相似文献
3.
Individual X-ray photons in the keV energy range produce hundreds of photoelectrons in a single pixel of a CCD array detector.
The number of photoelectrons produced is a linear function of the photon energy, allowing the measurement of spectral information
with an imaging detector system. Most solar X-ray telescopes, such as Yohkoh/SXT and Hinode/XRT, use CCD detectors in an integrating mode and are designed to make temperature estimates from multiband filter photometry.
We show how such instruments can be used in a new way to perform a limited type of this photon spectroscopy. By measuring
the variance in intensity of a series of repeated images through a single filter of an X-ray source, the mean energy per detected
photon can be determined. This energy is related to the underlying coronal spectrum, and hence it can be used to deduce the
mean plasma temperature. We apply this technique to data from the Yohkoh Soft X-Ray Telescope and compare the temperatures obtained with this technique with the temperatures derived using the standard
filter ratio method for a postflare loop system. Given the large dynamic range of the soft X-ray flux observed from the Sun,
we describe the requirements for a future instrument that would be better suited to performing photon spectroscopy.
B.J. Labonte deceased 24 October 2005. 相似文献
4.
Observational results from the supersoft X-ray detector (SD) aboard the spacecraft Shenzhou-2 are briefly described. The resultspertain to cosmic γ-ray bursts solar x-ray bursts, high-energy charged particles and soft X-ray background radiation. The detector is a proportional counter with a polypropylene thin-film window of 50 mm diameter, it operates in the energy range 0.23–3.0keV covered by six energy channels. Two grades of time resolution are used: 40 ms for recording burst events and 520 ms when there is no triggering signal resulted from a burst event. Figures 1 and 2 show the light curves and energy spectra of two cosmic γ-ray bursts (starting time 2001 Jan 17, 09:37:25.21 UT and 2001 Mar 9, 12:33:55.692 UT), and Figures 3 and 4, the results on two solar X-ray burst (2001 Apr 6, 19:14:09.11 UT, and 2001 May 20, 06:02:12.58 UT). The detector records the ambient high-energy charged particles when there is no burst event and the shutter of the window is closed. 110 data sets of high-energy charged particles along the spacecraft orbit have been collected. As examples, the variations of the particle counting rate along the orbit are shown in Figs. 6a, 6b, 8e, 8f and 7. More than 10 events of particle precipitation induced by solar proton events have also been recorded, some of which are displayed in Figs.6c–6f and 7. Some of the data of soft X-ray background radiation shown in Fig. 8 were obtained when the shutter was open, and they are important for the data processing of the burst events. 相似文献
5.
OPTIMA is a small, versatile high-speed photometer which is primarily intended for time resolved observations of young high
energy pulsars at optical wavelengths. The detector system consists of eight fiber fed photon counters based on avalanche
photodiodes, a GPS timing receiver, an integrating CCD camera to ensure the correct pointing of the telescope and a computerized
control unit. Since January 1999 OPTIMA proves its scientific potential by measuring a very detailed light-curve of the Crab
Pulsar as well as by observing cataclysmic variable stars on very short timescales. In this article we describe the design
of the detector system focussing on the photon counting units and the software control which correlates the detected photons
with the GPS timing signal.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
John Krizmanic Brian Morgan Robert Streitmatter Neil Gehrels Keith Gendreau Zaven Arzoumanian Reza Ghodssi Gerry Skinner 《Experimental Astronomy》2005,20(1-3):299-306
Diffractive optics, such as Phase Fresnel Lenses (PFL's), offer the potential to achieve excellent imaging performance in the x-ray and gamma-ray photon regimes. In principle, the angular resolution obtained with these devices can be diffraction limited. Furthermore, improvements in signal sensitivity can be achieved as virtually the entire flux incident on a lens can be concentrated onto a small detector area. In order to verify experimentally the imaging performance, we have fabricated PFL's in silicon using gray-scale lithography to produce the required Fresnel profile. These devices are to be evaluated in the recently constructed 600-meter x-ray interferometry testbed at NASA/GSFC. Profile measurements of the Fresnel structures in fabricated PFL's have been performed and have been used to obtain initial characterization of the expected PFL imaging efficiencies. 相似文献
7.
OPTIMA is a small, versatile high-speed photometer which is primarily intended for time resolved observations of young high energy pulsars at optical wavelengths. The detector system consists of eight fiber fed photon counters based on avalanche photodiodes, a GPS timing receiver, an integrating CCD camera to ensure the correct pointing of the telescope and a computerized control unit. Since January 1999 OPTIMA proves its scientific potential by measuring a very detailed light-curve of the Crab Pulsar as well as by observing cataclysmic variable stars on very short timescales. In this article we describe the design of the detector system focussing on the photon counting units and the software control which correlates the detected photons with the GPS timing signal. 相似文献
8.
P. Bergamini G. Bonelli A. Paizis L. Tommasi M. Uslenghi R. Falomo G. Tondello 《Experimental Astronomy》2000,10(4):457-471
The scientific performance evaluation of a photon countingimaging system is presented. The detector is constituted by an ICCD camera with RbTe photocathode(optimized for UV radiation), and dedicated electronics for the acquisition and analysis ofthe events. For each photon event on the CCD, a real-time centroid calculation is performed, inorder to reach spatial resolution down to 25 m FWHM. The system has been tested usingthe 182 cm telescope of the Asiago Observatory.A standard stars field through U Johnson filter,and the Crab pulsar (PSR 0531+21) were observed. From the photometric data, relative magnitudes of the standard stars have been derived, showing a goodlinearity of the detector in the range of flux under consideration, as expected fromprevious laboratory measurements.The pulsar's data have been processed by FFT and epoch foldingtechniques to testthe detector's timing performances in the highest resolutionmode (4.512 ms).These observations show that a space resolved time analysis ofperiodic sources can be performed with 10-7 s accuracy. 相似文献
9.
The polarisation of astrophysical source emission in the energy range from a few tens of keV up to the MeV region is an almost
unexplored field of high-energy astrophysics. Till date, polarimetry in astrophysics–in the energy domain from hard X-rays
up to soft γ-rays–has not been pursued due to the difficulties involved in obtaining sufficient sensitivity. Indeed for those
few instruments that are capable of performing this type of measurement (e.g. the COMPTEL instrument on the Compton Gamma-ray
Observatory and the IBIS instrument on INTEGRAL), polarimetry itself plays a secondary role in the mission objectives, as
the efficiencies (0.5% and 10% maximum, respectively) and polarimetric Q factors (0.1 and 0.3, respectively) are relatively limited. In order to perform efficient polarimetric measurements for hard
X-ray and soft gamma-ray sources, with an instrument of relatively robust and simple design, a CdTe based telescope (CIPHER:
Coded Imager and Polarimeter for High Energy Radiation) is under study. This instrument is based on a thick (10 mm) CdTe position-sensitive
spectrometer comprising four modules of 32 × 32 individual pixels, each with a surface area of 2 × 2 mm2 (about 160 cm2 total detection area). The polarimetric performance and design optimisation of the CIPHER detection surface have been studied
by use of a Monte Carlo code. This detector, due to its intrinsic geometry, can allow efficient polarimetric measurements
to be made between 100 keV and 1 MeV. In order to predict the polarimetric performance and to optimise the design and concept
of the CIPHER detection plane, a Monte Carlo code based on GEANT4 library modules was developed to simulate the detector behaviour
under a polarised photon flux. The Compton double event efficiency, as well bi-dimensional double event distribution maps
and the corresponding polarimetric modulation factor will be presented and discussed. Modulation Q factors better than 0.50 and double event total efficiencies greater than 10% were calculated in the energy range between
100 keV and 1 MeV. Herein we will present and discuss the general problems that affect polarimetric measurements in space,
such as the inclination of the source with respect to the telescope optical axis and background radiation. Q factor calculations for several beam inclinations as well as for background together with simulated astronomical sources
will be presented and discussed. 相似文献
10.
Joice Mathew S. Ambily Ajin Prakash Mayuresh Sarpotdar K. Nirmal A. G. Sreejith Margarita Safonova Jayant Murthy Noah Brosch 《Experimental Astronomy》2018,45(2):201-218
Though the ultraviolet (UV) domain plays a vital role in the studies of astronomical transient events, the UV time-domain sky remains largely unexplored. We have designed a wide-field UV imager that can be flown on a range of available platforms, such as high-altitude balloons, CubeSats, and larger space missions. The major scientific goals are the variability of astronomical sources, detection of transients such as supernovae, novae, tidal disruption events, and characterizing active galactic nuclei variability. The instrument has a 80 mm aperture with a circular field of view of 10.8 degrees, an angular resolution of ～22 arcsec, and a 240 - 390 nm spectral observation window. The detector for the instrument is a Microchannel Plate (MCP)-based image intensifier with both photon counting and integration capabilities. An FPGA-based detector readout mechanism and real time data processing have been implemented. The imager is designed in such a way that its lightweight and compact nature are well fitted for the CubeSat dimensions. Here we present various design and developmental aspects of this UV wide-field transient explorer. 相似文献
11.
C. Brocksopp R. L. C. Starling P. Schady K. O. Mason E. Romero-Colmenero E. M. Puchnarewicz 《Monthly notices of the Royal Astronomical Society》2006,366(3):953-968
We present XMM–Newton /EPIC spectra for the Laor et al. sample of Palomar Green (PG) quasars. We find that a power law provides a reasonable fit to the 2–5 keV region of the spectra. Excess soft X-ray emission below 2 keV is present for all objects, with the exception of those known to contain a warm absorber. However, a single power law is a poor fit to the 0.3–10.0 keV spectrum and instead we find that a simple model, consisting of a broken power law (plus an iron line), provides a reasonable fit in most cases. The equivalent width of the emission line is constrained in just 12 objects but with low (<2σ) significance in most cases. For the sources whose spectra are well fitted by the broken-power-law model, we find that various optical and X-ray line and continuum parameters are well correlated; in particular, the power-law photon index is well correlated with the FWHM of the Hβ line and the photon indices of the low- and high-energy components of the broken power law are well correlated with each other. These results suggest that the 0.3–10 keV X-ray emission shares a common (presumably non-thermal) origin, as opposed to suggestions that the soft excess is directly produced by thermal disc emission or via an additional spectral component. We present XMM–Newton Optical Monitor (OM) data, which we combine with the X-ray spectra so as to produce broad-band spectral energy distributions (SEDs), free from uncertainties due to long-term variability in non-simultaneous data. Fitting these optical–UV spectra with a Comptonized disc model indicates that the soft X-ray excess is independent of the accretion disc, confirming our interpretation of the tight correlation between the hard and soft X-ray spectra. 相似文献
12.
Sudhir Kumar Gupta Shibu K. Mathew P. Venkatakrishnan 《Journal of Astrophysics and Astronomy》2006,27(2-3):315-320
The index of scintillation measurement is a good parameter to compare different sites for image quality or ‘seeing’. We have
developed a scintillometer, which is deployed on the high resolution SPAR telescope in the island site of Udaipur Solar Observatory,
for the site characterization to specify the proposed MAST (Multi Application Solar Telescope). The scintillometer consists
of a miniature telescope, termed as micro telescope (4 mm aperture, 15 mm focal length) mounted on a drive which tracks the
Sun continuously, associated amplifiers and a data acquisition system. A photodiode is used as the detector. The telescope
along with detector was obtained from National Solar Observatory (NSO), and is similar to the one used for Advanced Technology
Solar Telescope (ATST) site survey. At USO we developed the amplifier and data acquisition system for the scintillometer.
A 24-bit analog to digital converter based system was designed, assembled, tested and used as the data acquisition system
(DAS). In this paper, we discuss the instrumentation and present the initial results. 相似文献
13.
The CdZnTe array detector is a new type of semiconductor detector being rapidly developed in recent years. It possesses a high spatial resolution and a high energy resolution, and it can work at room temperatures. This paper describes the physical properties and working principle of the CdZnTe array detector, as well as the manufacturing technology, including the chip pretreatment, passivation, ohmic electrode preparation, array template selection, and array packaging technology (micro-interconnection). For evaluating the perfor-mance of the detector, the authors have developed successfully a 4 pixel×4 pixel CdZnTe array and an 8 pixel×8 pixel CdZnTe array (with the thicknesses of 5 mm and 2 mm, the pixel size of 2 mm×2 mm, and the gaps of 0.15 mm and 0.2 mm, respectively) in cooperation with the partner. A multi-channel electronic readout system based on the ASIC (Application Specific Integrated Circuit) chip is devel-oped independently for the charge measurement of the 4 pixel×4 pixel CdZnTe array. The energy spectra and corresponding energy resolutions of the 16 pixels are obtained with the 137Cs radiative source, among them the best resolution is 4.8%@662 kev. 相似文献
14.
Radio noise storms show that suprathermal electrons (a few tens of keV) are present in the vicinity of active regions during several hours or even a few days. Where and how these electrons are energized is not yet well known. A flare-like sudden energy release in the active region is in general observed at the onset of noise storms, either as a fully developed flare or, more often, as a soft X-ray brightening without conspicuous H signature. In order to investigate to what extent electrons energized in the active region contribute to the noise-storm emission in the overlying coronal structures, we combine radio imaging (Nançay radioheliograph) with X-ray spectral observations at photon energies of a few keV (GOES) and - for the first time - around 10 keV (WATCH/GRANAT). In two of four studied events the WATCH data show a significant excess of the deka-keV count rate above the expectation from an isothermal fit to the GOES fluxes. Although the electron population producing the deka-keV X-ray emission would be energetic enough to power the simultaneous radio noise storm, the much longer duration of the radio emission requires time-extended particle acceleration. The acceleration probably occurs in the corona overlying the X-ray emitting region, triggered by the processes which give rise to the X-ray brightenings. 相似文献
15.
D. E. Roa R. K. Smither X. Zhang K. Nie Y. Y. Shieh N. S. Ramsinghani N. Milne J. V. Kuo J. L. Redpath M. S. A. L. Al-Ghazi P. Caligiuri 《Experimental Astronomy》2005,20(1-3):229-239
The objective of this project is to develop and construct an innovative imaging system for nuclear medicine and molecular imaging that uses photon diffraction and is capable of generating 1–2 mm spatial resolution images in two or three dimensions. The proposed imaging system would be capable of detecting radiopharmaceuticals that emit 100–200 keV gamma rays which are typically used in diagnostic nuclear medicine and in molecular imaging. The system is expected to be optimized for the 140.6 keV gamma ray from a Tc-99m source, which is frequently used in nuclear medicine. This new system will focus the incoming gamma rays in a manner analogous to a magnifying glass focusing sunlight into a small focal point on a detector's sensitive area. Focusing gamma rays through photon diffraction has already been demonstrated with the construction of a diffraction lens telescope for astrophysics and a scaled-down lens for medical imaging, both developed at Argonne National Laboratory (ANL). In addition, spatial resolutions of 3 mm have been achieved with a prototype medical lens. The proposed imaging system would be comprised of an array of photon diffraction lenses tuned to diffract a specific gamma ray energy (within 100–200 keV) emitted by a common source. The properties of photon diffraction make it possible to diffract only one specific gamma ray energy at a time, which significantly reduces scattering background. The system should be sufficiently sensitive to the detection of small concentrations of radioactivity that can reveal potential tumor sites at their initial stages of development. Moreover, the system's sensitivity would eliminate the need for re-injecting a patient with more radiopharmaceutical if this patient underwent a prior nuclear imaging scan. Detection of a tumor site at its inception could allow for an earlier initiation of treatment and wider treatment options, which can potentially improve the chances for cure. 相似文献
16.
The VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an innovative design we proposed for a revolutionary photon detector. The main idea is to replace the classical dynode chain of a PMT with a SiPM (G-APD), the latter acting as an electron detector and amplifier. The aim is to match the large sensitive area of a photocathode with the performance of the SiPM technology. The VSiPMT has many attractive features. In particular, a low power consumption and an excellent photon counting capability. To prove the feasibility of the idea we first tested the performance of a special non-windowed SiPM by Hamamatsu (MPPC) as electron detector and current amplifier. Thanks to this result Hamamatsu realized two VSiPMT industrial prototypes. In this work, we present the results of a full characterization of the VSiPMT prototype. 相似文献
17.
低温制冷技术是下一代激光干涉仪引力波探测器的核心技术之一. 日本引力波探测器KAGRA (Kamioka Gravitational Wave Detector)作为该技术的前沿开拓者, 将运行在20K的超低温环境中, 并使用在低温下热噪声较低的单晶蓝宝石晶体作为测试镜. 然而, 高质量大尺寸低吸收率的蓝宝石晶体极难制备. 此外, 由于蓝宝石晶体存在晶格结构不均匀, 很容易导致不必要的双折射效应, 从而影响探测器的目标灵敏度. 基于上述问题, 开发了两套大尺寸光学测量系统, 首次系统研究了KAGRA低温蓝宝石测试镜的光学特性. 首先, 根据探测器对测试镜热噪声的要求, 开发了一套基于光热共光路干涉技术的光学测量系统, 该系统可对测试镜以及测试镜表面涂层的光学吸收进行有效的表征. 其次, 基于光学吸收测量系统, 开发了一套双折射效应测量系统, 该系统可以有效表征测试镜中双折射的均匀性. 目前两套测量系统的搭建与调试已完成, 对蓝宝石测试镜光学吸收的测量灵敏度达到了1.5ppm/cm, 双折射测量系统的空间分辨率小于0.3mm times 0.3mm. 该工作对降低大尺寸低温测试镜双折射效应及提高探测器灵敏度具有重要意义. 相似文献
18.
David Salvetti Martino Marelli Fabio Gastaldello Simona Ghizzardi Silvano Molendi Andrea De Luca Alberto Moretti Mariachiara Rossetti Andrea Tiengo 《Experimental Astronomy》2017,44(3):309-320
We present an accurate characterization of the particle background behaviour on XMM-Newton based on the entire EPIC archive. This corresponds to the largest EPIC data set ever examined. Our results have been obtained thanks to the collaboration between the FP7 European program EXTraS and the ESA R&D ATHENA activity AREMBES. We used as a diagnostic an improved version of the diagnostic which compares the data collected in unexposed region of the detector with the region of the field of view in the EPIC-MOS. We will show that the in Field-of-View excess background is made up of two different components, one associated to flares produced by soft protons and the other one to a low-intensity background. Its origin needs to be further investigated. 相似文献
19.
A facility for the registration of light fluxes meant for the study of their properties with high temporal resolution is described. The “Quantochron 4-48” acquisition facility measures the photon arrival times using periodic signals of three types-second-long period signals (pps), 10-kHz, and 30-MHz signals. The first two come from a GPS, whereas the latter signal comes from the PCI bus of the computer connected to the facility. These time scales are used to produce for each time instant a 28-bit time code supplemented by 48 bits bearing the information about the coordinates, energy, and polarization of the photon at the output of the detector. The sequence of complete 64-bit words is buffered in FIFO memory and sent to computer RAM. The device has as its base element a XILINX SPARTAN XCS40XL PQ240AKP0505 microchip incorporated into a PCI slot. The registration facility consists of two PC servers equipped with these boards and a control computer. The facility determines the photon arrival times to within 30 ns with a dead time of 30 ns and maximum lossless count rate of 106 photons/s. The registration facility allows continuous recording of detector counts over 17 hours with a one microsecond World-Time (UT) calibration accuracy. 相似文献
20.
R. Poggiani 《Experimental Astronomy》2004,18(1-3):109-132
The domain of high speed optical astrophysics is still quite unexplored. The availability of 10 meter diameter telescopes
offers the unique possibility to investigate variability of faint objects at submillisecond time scales. In this paper I describe
the concepts of a photometer and a spectrometer for high speed astronomical observations. The instruments are based on a photon
counting detector developed for high energy physics, the Visible Light Photon Counter (VLPC). The detector has a quantum efficiency
in the visible as high as 88% and performs photon counting with sub microsecond time resolution. The photometer is built using
VLPC arrays. Adding a grating a VLPC array can be used in a time resolved spectrograph with medium resolution. This paper
develops, starting from experimental data, the concept of the two VLPC based instruments and their application to time resolved
photometry and spectroscopy of compact objects (pulsars, cataclysmic variables, low mass X-ray binary systems etc) and optical
counterparts of Gamma Ray Bursts. The high speed optical observations are the ideal complement to X/γ rays and gravitational
wave studies. The application of the instruments to the optical photometry of pulsars, the spectrophotometry of the prompt
optical flash from Gamma Ray Bursts and the study of binary systems are discussed in detail: in the last two applications
the instruments offer better opportunities than existing instruments. 相似文献