共查询到20条相似文献，搜索用时 937 毫秒
1.
V. L. Plokhotnichenko G. M. Beskin V. G. de Bur S. V. Karpov D. A. Bad’in Z. V. Lyubetskaya A. P. Lyubetskij V. V. Pavlova 《Astrophysical Bulletin》2009,64(3):308-316
A hardware and software complex of the MANIA experiment designed to search for and study the photometric variability of astrophysical objects with a temporal resolution of 10?6 s is described. The panoramic photospectropolarimeter uses interchangeable optical units, which allow the observations to be performed in four modes—spectroscopic, spectropolarimetric, photometric, and polarimetric. A coordinate—sensitive detector equipped with a set of microchannel plates is capable of recording flux fluctuations from objects and comparison stars simultaneously in different photometric bands and in different polarization planes. The Quantochron 4–48 data acquisition facility operating on line with a computer acquires observational data with a temporal resolution of 1microsecond. The methods of analysis of panoramic data with high temporal resolution are discussed. 相似文献
2.
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
3.
D. L. Khokhlov 《Astrophysics and Space Science》2013,343(2):787-790
Constraints of the laboratory physics on the model of the universe are considered. The constraints are derived from the measurement procedure for the flux of electromagnetic radiation and valid for any model of the universe. In classical physics, an observer in the frame of the detector can measure the transformation (1+z)?1 for the energy flux of the electromagnetic wave emitted in the frame of the source but cannot any transformation for space and time between the frames of the source and detector. In quantum mechanics, the energy of the electromagnetic radiation as a function of the distance may be measured as a redshifted frequency of photon (1+z) or as a decrease of the intensity of radiation (1+z). 相似文献
4.
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
5.
R. Rocchia M. Arnaud C. Blondel M. Cantin B. Mougin R. Rothenflug A. Tarrius 《Astrophysics and Space Science》1983,96(2):361-374
A multiplexX-ray image analyser is described. It consists in a time-modulated coded aperture associated with a solid state detector. The system combines the high efficiency and good spectral resolution of solid state spectrometers with the spatial resolution of the coded aperture (200 ).The device can be installed at the focus of a grazing incidence telescope to make images and spectra of faint astronomicalX-ray sources. 相似文献
6.
《Astroparticle Physics》2009,30(6):287-292
The ARGO-YBJ experiment is mainly devoted to search for astronomical gamma sources. The arrival direction of air showers is reconstructed thanks to the times measured by the pixels of the detector. Therefore, the timing calibration of the detector pixels is crucial in order to get the best angular resolution and pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore an off-line software calibration has been adopted. Here, the details of the procedure and the results are presented. 相似文献
7.
T. Chattopadhyay S. V. Vadawale A. R. Rao S. Sreekumar D. Bhattacharya 《Experimental Astronomy》2014,37(3):555-577
Astrosat is the first Indian satellite mission dedicated for astronomical studies. It is planned for launch during 2014 and will have five instruments for multi-wavelength observations from optical to hard X-rays. Cadmium Zing Telluride Imager (CZTI) is one of the five instruments aiming for simultaneous X-ray spectroscopy and imaging in the energy range of 10 keV to 100 keV (along with all sky photometric capability unto 250 keV). It is based on pixilated CZT detector array with total geometric area of 1024 cm2. It will have two-dimensional coded mask for medium resolution X-ray imaging. The CZT detector plane will be realized using CZT detector modules having integrated readout electronics. Each CZT detector module consists of 4 cm × 4 cm CZT with thickness of 5 mm which is further pixilated into 16 × 16 array of pixels. Thus each pixel has size of 2.5 mm × 2.5 mm and thickness of 5 mm. Such pixilated detector plane can in principle be used for hard X-ray polarization measurements based on the principle of Compton scattering by measuring azimuthal distribution of simultaneous events in two adjacent pixels. We have carried out detailed Geant4 simulations for estimating polarimetric capabilities of CZTI detector plane. The results indicate that events in the energy range of 100 keV to 250 keV, where the 5 mm thick CZT detector has significant detection efficiency, can be used for polarimetric studies. Our simulation results indicate the minimum detectable polarization (MDP) at the level of ～ 10% can be achieved for bright Crab like X-ray sources with exposure time of ～500 ks. We also carried out preliminary experiments to verify the results from our simulations. Here we present detailed method and results of our simulations as well as preliminary results from the experimental verification of polarimetric capabilities of CZT detector modules used in Astrosat CZTI. 相似文献
8.
Mayuresh Sarpotdar Joice Mathew A. G. Sreejith Nirmal K. S. Ambily Ajin Prakash Margarita Safonova Jayant Murthy 《Experimental Astronomy》2017,43(1):99-117
We have developed a low-cost off-the-shelf component star sensor (StarSense) for use in minisatellites and CubeSats to determine the attitude of a satellite in orbit. StarSense is an imaging camera with a limiting magnitude of 6.5, which extracts information from star patterns it records in the images. The star sensor implements a centroiding algorithm to find centroids of the stars in the image, a Geometric Voting algorithm for star pattern identification, and a QUEST algorithm for attitude quaternion calculation. Here, we describe the software package to evaluate the performance of these algorithms as a star sensor single operating system. We simulate the ideal case where sky background and instrument errors are omitted, and a more realistic case where noise and camera parameters are added to the simulated images. We evaluate such performance parameters of the algorithms as attitude accuracy, calculation time, required memory, star catalog size, sky coverage, etc., and estimate the errors introduced by each algorithm. This software package is written for use in MATLAB. The testing is parametrized for different hardware parameters, such as the focal length of the imaging setup, the field of view (FOV) of the camera, angle measurement accuracy, distortion effects, etc., and therefore, can be applied to evaluate the performance of such algorithms in any star sensor. For its hardware implementation on our StarSense, we are currently porting the codes in form of functions written in C. This is done keeping in view its easy implementation on any star sensor electronics hardware. 相似文献
9.
A new imaging balloon-borne telescope for hard X-rays in the energy range from 30 to 100 keV is described. The imaging capability is provided by the use of an extended URA-based coded-mask. With only one motor and suitable stop pins, we can rotate a carbon-fiber wheel with most of the mask elements attached to it by 180°, and a bar, which is also part of the mask pattern and is allowed to rotate freely over the wheel, by 90°; this combined rotation creates an antimask of the original mask, except for the central element. This is a novel and elegant manner of providing an antimask without additional weight and complex mechanical manipulations. We show that the use of antimasks is a very effective method of eliminating systematic variations in the background map over the position-sensitive detector area. The expected sensitivity of the instrument for the 30–100 keV range is of the order of 7 × 10-5 photons cm-2 s-1 keV-1, for an integration time of 104 seconds at a residual atmosphere of 3.5 g cm-2. This telescope will provide imaging observations of bright galactic hard X-ray sources with an angular resolution of 2° in a 10° by 10° FOV, which is defined by a collimator placed in front of the detector system. We are particularly interested in the galactic center region, where recent imaging results in X-rays have shown the presence of an interesting source field. Results of computer simulations of the imaging system are reported. 相似文献
10.
An observation carried out with a balloon-borne detector of an additional flux of secondary X-rays (E 30 keV) at large depths in the atmosphere is described. This excess is attributed to the emission of very hard X-rays during the solar flare of August 7, 1972. The propagation in the atmosphere of the secondary photons resulting from their electromagnetic interactions in the air is computed by utilizing the Monte Carlo method. The computations agree with the observed flux when a very hard solar X-ray spectrum is assumed. 相似文献
11.
A flare rising from behind the solar limb was recorded simultaneously by the UCSD X-ray detector on OSO-III (7.7–200 keV)
and the Caltech photoheliograph on Robinson Laboratory roof (Hα). The de-occultation gives excellent spatial resolution of
the X-ray source. Spectra suggest that the material was already heated to 27 000 000° and that the increase in flux was due
to the de-occultation. The flux rise to maximum was proportional to the apparent area. The uniformity of this rise shows that
there was no special kernel of emission. Comparison of the deduced volume with the bremsstrahlung formula gives a density
of about 1010 for the 27 000 000° component of the flare; this is confirmed by consideration of the maximum possible coulomb braking. The
actual decay is more likely by escape rather than coulomb braking. 相似文献
12.
R. Morales A. C. Fabian C. S. Reynolds 《Monthly notices of the Royal Astronomical Society》2000,315(1):149-154
The variable warm absorber seen with ASCA in the X-ray spectrum of MCG–6-30-15 shows complex time behaviour in which the optical depth of O viii anticorrelates with the flux whereas that of O vii is unchanging. The explanation in terms of a two-zone absorber has since been challenged by BeppoSAX observations. These present a more complicated behaviour for the O viii edge. We demonstrate here that the presence of a third, intermediate, zone can explain all the observations. In practice, warm absorbers are likely to be extended, multi-zone regions of which only part causes directly observable absorption edges at any given time. 相似文献
13.
Reconstruction of objects by direct demodulation 总被引：3，自引：0，他引：3
High resolution reconstruction of complicated objects from incomplete and noisy data can be achieved by solving modulation equations iteratively under physical constraints. This direct demodulation method is a powerful technique for dealing with inverse problem in general case. Spectral and image restorations and computerized tomography are only particular cases of general demodulation. It is possible to reconstruct an object in higher dimensional space from observations by a simple lower dimensional instrument through direct demodulation. Our simulations show that wide field and high resolution images of space hard X-rays and soft-rays can be obtained by a collimated non-position-sensitive detector without coded aperture masks. 相似文献
14.
O. M. Yizhakevych V. M. Andruk L. K. Pakuliak 《Kinematics and Physics of Celestial Bodies》2017,33(3):142-148
A catalog of 1385 astrometric positions of Saturn’s moons S2–S9 has been compiled with Tycho-2 as a reference frame from photographic observations obtained at the Main Astronomical Observatory, National Academy of Sciences of Ukraine, in 1961–1990. Astronegatives have been digitized with an Epson Expression 10000XL commercial scanner in 16-bit grayscale with a resolution of 1200 dpi. Reduction has been performed in the LINUX-MIDAS-ROMAFOT software supplemented with additional modules. The internal positional accuracy of the reduction is 0.09…0.23′′ for both coordinates and 0.27…0.37m for the photographic magnitudes of the Tycho-2 catalog. The calculated topocentric positions of the moons are compared online with the IMCCE ephemeris data (DE405 + TASS1,7). Moon-minus-moon differential coordinates are found for most of the moons and compared with theoretical data (http://lnfm1.sai.msu.ru/neb/nss/nssephmr.htm). 相似文献
15.
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
16.
17.
For the opportunities of CCD observations to be pursued, we have produced a precision system for telescope sidereal tracking.
Using the software and hardware complex, one can control the system both autonomously and via a personal computer. 相似文献
18.
The current supernova detection technique used in IceCube relies on the sudden deviation of the summed photomultiplier noise rate from its nominal value during the neutrino burst, making IceCube a ≈3 Megaton effective detection volume - class supernova detector. While galactic supernovae can be resolved with this technique, the supernova neutrino emission spectrum remains unconstrained and thus presents a limited potential for the topics related to supernova core collapse models.The paper elaborates analytically on the capabilities of IceCube to detect supernovae through the analysis of hits in the detector correlated in space and time. These arise from supernova neutrinos interacting in the instrumented detector volume along single strings. Although the effective detection volume for such coincident hits is much smaller (?35 kton, about the scale of SuperK), a wealth of information is obtained due to the comparatively low rate of coincident noise hits. We demonstrate that a neutrino flux from a core collapse supernova will produce a signature enabling the resolution of rough spectral features and, in the case of a strong signal, providing indication on its location.We further discuss the enhanced potential of a rather modest detector extension, a denser array in the center of IceCube, within our one dimensional analytic calculation framework. Such an extension would enable the exploration of the neutrino sky above a few GeV and the detection of supernovae up to a few 100’s of kilo parsec. However, a 3-4 Mpc detection distance, necessary for routine supernova detection, demands a significant increase of the effective detection volume and can be obtained only with a more ambitious instrument, particularly the boosting of sensor parameters such as the quantum efficiency and light collection area. 相似文献
19.
John Vallerga Jason McPhate Anton Tremsin Oswald Siegmund 《Astrophysics and Space Science》2009,320(1-3):247-250
At the heart of future space-based astronomical UV instruments will be a sensitive UV detector. Though there has been a death of new UV mission opportunities, detector development has continued. Improvements have been made in spatial resolution, dynamic range, detector size, quantum efficiency and background. At the same time the power and mass required to achieve these goals have decreased. We review the current capabilities of microchannel plate based detectors at Berkeley, both in the laboratory and aboard current on-orbit spacecraft. We also discuss what can be expected from the next generation of UV detectors over the next decade. 相似文献
20.
John A. Regan Martin G. Haehnelt Matteo Viel 《Monthly notices of the Royal Astronomical Society》2007,374(1):196-205
We compare simulations of the Lyman α forest performed with two different hydrodynamical codes, gadget-2 and enzo . A comparison of the dark matter power spectrum for simulations run with identical initial conditions show differences of 1–3 per cent at the scales relevant for quantitative studies of the Lyman α forest. This allows a meaningful comparison of the effect of the different implementations of the hydrodynamic part of the two codes. Using the same cooling and heating algorithm in both codes, the differences in the temperature and the density probability distribution function are of the order of 10 per cent. The differences are comparable to the effects of box size and resolution on these statistics. When self-converged results for each code are taken into account, the differences in the flux power spectrum – the statistics most widely used for estimating the matter power spectrum and cosmological parameters from Lyman α forest data – are about 5 per cent. This is again comparable to the effects of box size and resolution. Numerical uncertainties due to a particular implementation of solving the hydrodynamic or gravitational equations appear therefore to contribute only moderately to the error budget in estimates of the flux power spectrum from numerical simulations. We further find that the differences in the flux power spectrum for enzo simulations run with and without adaptive mesh refinement are also of the order of 5 per cent or smaller. The latter require 10 times less CPU time making the CPU time requirement similar to that of a version of gadget-2 that is optimized for Lyman α forest simulations. 相似文献