共查询到20条相似文献，搜索用时 625 毫秒
1.
One of the major goals in VHE--ray astronomy is to open the energy range below 100 GeV with earthbound detectors. This paper demonstrates a new method for analyzing erenkov light of a shower in a erenkov telescope array. This method is successful for showers in this low energy regime where previous techniques (e.g. alpha analysis) are not applicable. A Monte Carlo simulation is applied to a system of 19 Whipple type [3, Cawley 1990] Imaging Atmospheric erenkov telescopes (IAT), each built as a 10 m diameter reflector and equipped with a 109 photomultiplier tube camera. The energy threshold for a single detector of this type is given [5, Kerrick et al. 1995] as 250 GeV. Analysis of simulated coincident events of the system for those events not having enough light to apply a standard imaging analysis [4, Hillas 1985], leads to a considerably lower threshold of 85 GeV. With a new analysis method of these events it is shown that it should be possible to distinguish between -ray induced and proton induced showers. The improvement of sensitivity (Q = figure of merit) of this analysis method is found to be Q=2.9. 相似文献
2.
Present Observational Status of the Intermediate Mass Stars: δ Sct Stars, γ Dor Stars and roAp Stars
D.W. Kurtz 《Astrophysics and Space Science》2003,284(1):29-36
The present observational status of the Sct stars, Dor stars and roAp stars is discussed. The Sct stars are the most intensively observed of the three groups, but it has become clear that there are severe problems in extracting asteroseismic information from them. Dozens of frequencies are observed, but hundreds of frequencies are predicted from the models; unique matches of observation and theory still elude us. The Sct stars are observationally complex – some recent `best case' campaigns are discussed. It is possible that substantial observational advances for Sct stars may need to await upcoming satellite missions. New Dor stars are beingdiscovered frequently, and new behaviour is being found for them. They constitutean observationally young field. Their pulsational frequency range is being expanded, their position in the HR diagram is becoming better known (but is yet to be fully constrained), and the possibility exists of hybrid Dor – Sct stars that have greatasteroseismic promise, although it is clear such stars are rare, if they do exist. It has been observationally challenging to extract more than a fewfrequencies for any Dor star so far. Exciting spectroscopic discoveries of new behaviour in roAp stars promise unprecedented information about the structure of the peculiar atmospheres ofthose stars – pulsation amplitude and phase in 3D, magnetic field structurein 3D, abundance stratification in 3D, realistic T- for the most peculiarstars – as well as entirely new information about the interaction of pulsation,rotation and magnetic fields. Recent theoretical work has led to new understandingof the previously inexplicable frequency spacing of HR 1217 with new Whole Earth Telescope observations supporting this theory. An `improved oblique pulsator model' has been developed in which the pulsationaxis is not the magnetic axis; this model has passed several observationaltests and new ones are being devised to examine it further. 相似文献
3.
K. T. Brazier A. Carramiñana P. M. Chadwick T. R. Currell N. A. Dipper E. W. Lincoln V. G. Mannings T. J. L. McComb K. J. Orford S. M. Rayner K. E. Turver 《Experimental Astronomy》1989,1(2):77-99
The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence guard ring technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes. 相似文献
4.
P. O. Lagage G. Oloffson S. Cabrit C. Cesarsky L. Nordh J. M. Rodriguez Espinosa 《Experimental Astronomy》1994,3(1-4):163-164
The region around the Herbig Ae/Be star LkH198 was imaged at 10m with the CAMIRAS camera at the Canada-France-Hawaii Telescope and the Nordic Optical Telescope. We discovered a deeply embedded companion 6 north of LkH198, which may be responsible for most of the far-infrared emission in the region and for driving the molecular flow. LkH198 appears point-like at our resolution (FWHM 1.3), excluding an extended envelope of transiently heated small grains as the dominant origin of the mid-infrared excess in that star. 相似文献
5.
F. W. Stecker 《Astrophysics and Space Science》1970,6(3):377-389
The cosmic -ray spectrum below 1 GeV arising from cosmic ray p-p interactions is calculated. Its characteristics are determined by the properties of secondary neutral pion production occurring at accelerator energies. A model is chosen for numerical calculations in which the two dominant modes of neutral pion production at accelerator energies are the production of the (1.238) isobar and one fireball. The effect of -p and p- interactions on the cosmic -ray spectrum is also calculated. The final results are given in terms of both differential and integral -ray energy spectra. 相似文献
6.
We have used the ESO 10 m camera, TIMMI, to image with a very high angular resolution (PFoV: 0.3; FWHM:0.9) several main-sequence star disk candidates. Information on the -Pictoris dust disk has been obtained in a region largely inaccessible to previous observations: 0–80 AU, with a resolution of about 5 AU after deconvolution. Another promising target for 10 m imaging, 51 Ophiuchi, appears point-like.based on data collected at the European Southern Observatory (ESO), La Silla, Chile 相似文献
7.
Toshio Fukushima 《Celestial Mechanics and Dynamical Astronomy》1997,68(2):121-137
We developed a method to solve Keplers equation for the hyperboliccase. The solution interval is separated into three regions; F 1, F 1, F 1. For the region F is large, we transformed the variablefrom F to exp F and applied the Newton method to the transformed equation.For the region F is small, we expanded the equation with respect to F andapplied the Newton method to the approximated equations. For the middleregion, we adopted a discretization of the Newton method and used the Taylorseries expansion for the evaluation of transcendental functions (Fukushima,1997). Numerical measurements showed that, in the case of Intel Pentiumprocessor, the new method is more than 3.7 times as fast as the combinationof a fourth order correction formula (Fukushima, 1997) and Roysstarting procedure (Roy, 1988) and others. 相似文献
8.
D. A. Lewis 《Experimental Astronomy》1990,1(4):213-226
In TeV -ray astronomy, large mirrors are used to collect erenkov light from electromagnetic cascades in the atmosphere in order to obtain low energy thresholds. The flux sensitivity of TeV -ray detectors is limited by background due to erenkov light bursts from isotropic, cosmic-ray showers which are much more numerous than -ray showers. It has recently been established that most of this background can be eliminated on the basis of the shapes of erenkov light images on the focal plane of a telescope. In order for this technique to work, the light collector must have adequate resolution over a relatively wide field of view. In this paper, the optical characteristics of the 10 m reflector used in the imaging detection of the Crab Nebula are examined and contrasted with those of a standard parabolic design. This 10 m reflector has a unique (Davies-Cotton) design with small spherical facet mirrors placed on spherical support structure with radius equal to exactly 1/2 the curvature radius of the facet mirrors. The off-axis focusing properties of this type of telescope have not been examined previously. 相似文献
9.
L. Bassani R. C. Butler A. J. Dean G. Di Cocco A. Della Ventura F. Perotti G. Villa 《Astrophysics and Space Science》1982,82(2):311-316
During a balloon flight in September 1979 of the MISO low-energy -ray telescope, the BL Lac-object MkN 501 was studied in the hard X-ray range above 30 keV and in the low energy -ray range up to 19 MeV. No statistically significant X- and -ray fluxes were detected. The implications of the upper limits obtained are discussed in the light of the relativistic jet theories recently proposed. 相似文献
10.
We describe initial results of a program to image massive newly-formed stars with sub-arc second spatial resolution. We discuss high-precision diffraction-limited size measurements at =10 m made using the 3 m Lick telescope. The point-spread function has FWHM 0.7; deconvolution yields a spatial resolution of 0.35. We find that the core component of one such object, LkH 101, is unresolved at these scales, and we are able to set a 95%-confidence upper limit of 270 AU for the diameter of the circumstellar dust shell. This places the dust at the same radial scale as a strong ionized stellar wind region seen at radio wavelengths. Our observations, when combined with published spectral observations, rule out an optically thick circumstellar disk but allow a radially thin, anisotropic distribution of dust, or alternatively an isotropic distribution of dust with a narrow range of large grain sizes. 相似文献
11.
We have started a program of high-resolution (0.4/pixel) 10m imaging of bipolar outflow sources using the 10m camera CAMIRAS. We present recent results obtained at the Canada France Hawaii Telescope which reveal extended emission or IR companions in several luminous objects. The extended emission we detected probably arises from transiently heated very small grains, while the newly discovered companions could contribute significantly to the outflow activity and extended far-IR emission usually attributed to the main optical source. 相似文献
12.
M. Aglietta P. Antonioli G. Badino G. Bologna C. Castagnoli A. Castellina V. L. Dadykin W. Fulgione P. Galeotti F. F. Khalchukov E. V. Korolkova P. V. Kortchaguin V. B. Kortchaguin V. A. Kudryavtsev A. S. Malguin L. Periale V. G. Ryassny O. G. Ryazhskaya O. Saavedra G. Trinchero S. Vernetto C. Vigorito V. F. Yakushev G. T. Zatsepin 《Astrophysics and Space Science》1995,231(1-2):355-358
A search for low energy neutrinos of all flavours in correlation with 553 ray bursts detected by BATSE aboard the Compton Observatory has been performed by the LSD (Liquid Scintillator Detector) neutrino telescope. No excess ofe,, orv
e,, candidate has been detected by LSD during the time interval in which BATSE detected the 90% of the photon flux for any of the GRBs analyzed. Upper limits on the neutrino fluxes are given in the paper. 相似文献
13.
M.G. Larionov 《Astrophysics and Space Science》1997,252(1-2):139-149
The possibility of using a Friedmann-Lemaître model with a non-zero cosmological constant is investigated on the basis of analyses of the RATAN-600 and 87GB radio surveys and optical constraints. A zero deceleration parameter and critical matter density are features of the model. The model is in agreement with current observational data, including estimates of the age of the Universe, Hubble constant measurements, and the - z relation. A value for the cosmological constant is determined and its physical nature discussed. 相似文献
14.
A. Akyüz D. Bhattacharya D. D. Dixon T. J. O'Neill O. T. Tümer R. S. White A. D. Zych 《Experimental Astronomy》1995,6(3):275-284
The proposed Tracking and Imaging Gamma-Ray Experiment (TIGRE), operating in the 0.3–100 MeV energy interval, will be an efficient polarimeter with a modulation factor of 50% at 0.5 MeV. The polarization detection parameters of TIGRE were estimated using a Monte Carlo simulation modified to include the polarization dependence of the Klein-Nishina formula. Using Compton scattering of low energy photons and approximately 3 acceptance angle after scattering, TIGRE will be able to measure strong sources with 20% fractional polarization at 3 significance in a typical balloon-borne exposure and 5% during a 4-week satellite observation. 相似文献
15.
Satoshi Hinata 《Astrophysics and Space Science》1978,55(2):427-439
We determine the momentum distribution of the relativistic particles near the Crab pulsar from the observed X- and -ray spectra (103109 eV), provided that the curvature radiation is responsible for it. The power law spectrum for the relativistic electrons,f()
–5, reproduces a close fit to the observed high-energy photon spectrum. The theoretically determined upper limit to the momentum (due to radiation damping),
M
8×106, corresponds to the upper cut-off energy of the -ray spectrum, 109 eV. The lower limit to the momentum,
m
1.8×105, is chosen such that flattening of the X-ray spectrum below 10 keV is simulated. The number density of these electrons is found to be much higher than the Goldreich-Julian density. We also discuss pulse shape and polarization of high-energy photons. The extremely high density of particles and the steep momentum spectrum are difficult to understand. This may imply that another, more efficient, mechanism is in operation. 相似文献
16.
We have produced high-resolution images of the nuclear region of M82 with SpectroCam-10, a mid-infrared instrument at the Palomar 5 m telescope. These images were taken at 11.7 m and 9.8 m with a 1m filter bandpass at the diffraction limit of 0.6 arcsec, making them the highest resolution maps yet available of M82. In addition, we have obtained high-resolution (/=2000) maps of the velocity field of the nuclear disk of M82 in the 12.81 m line emission of [NeII]. In these proceedings we present the 11.7 m image, which will appear together with the 9.8 m map and the [Ne II] spectra in a subsequent paper, now in preparation. This image shows very clearly a bridge structure joining the eastern and western clusters. 相似文献
17.
The propagation of cosmic ray electrons in the framework of the Disk-Halo diffusion model in which the diffusion coefficientD z
E
(wherez is the distance from the galactic plane andE is the energy), and the magnetic fieldHz
– has been examined by making use of the recently available radio data up to 8 GHz toward the Anticenter (A) and Halo Minimum (M). The following inferences are then made. From the difference in the frequency at which steepening occurs in the radio spectra towardA andH, it is found that the observations are consistent with the magnetic field decreasing withz such that =0.24–0.37. An electron injection spectrum with a single power law down to energies well below 1 GeV cannot explain satisfactorily the observed radio spectra. All observations, however, can be understood in a self consistent way if the observed steepening of the radio spectra, and hence the interstellar electron spectrum, is due partly to the deviation in the power law electron injection spectrum below a few GeV and partly to the first break arising from electron energy losses occurring in the same energy region. In this case, using the value of obtained above and a value of =0.3–0.6, it is found that the spectral index 0 of the injected electrons above a few GeV has a value between 1.9 and 2.3 and the index a value between 0.5 and 1. Further, if the electrons and protons have the same spectral shape at injection, then 0=2.1–2.3.NASA-NRC, Senior Research Associate on leave from Tata Institute of Fundamental Research, Bombay, India. 相似文献
18.
The power in the different modes of an expansion of the solar radial magnetic field at the surface in terms of Legendre polynomials,P , is calculated with the help of a solar dynamo model studied earlier. The model is of the Babcock–Leighton type, i.e., the surface eruptions of the toroidal magnetic field – through the tilt angle, , formed by the magnetic axis of a bipolar magnetic region with the east-west line – are the sources for the poloidal field. In this paper it is assumed that the tilt angle is subject to fluctuations of the form, = ()+ <> where <> is the average value and () is a random normal fluctuation with standard deviation which is taken from Howard's observations of the distribution of tilt angles. For numerical considerations, negative values of were not allowed. If this occurred, was recalculated. The numerical integrations were started with a toroidal magnetic field antisymmetric across the equator, large enough to generate eruptions, and a negligible poloidal field. The fluctuations in the tilt angle destroy the antisymmetry as time increases. The power of the antisymmetric modes across the equator (i.e., odd values of ) is concentrated in frequencies, p, corresponding to the cycle period. The maximum power lies in the =3 mode with considerable power in the =5 mode, in broad agreement with Stenflo's results who finds a maximum power at =5. For the symmetric modes, there is considerable power in frequencies larger than p, again in broad agreement with Stenflo's power spectrum. 相似文献
19.
Large field H observations of the Milky Way between Carina and Aquila were made through a narrow interference filter 15 wide. Characteristic large-scale features of the observed region are extended emission areas in Carina, Norma-Scorpius and Scutum-Sagittarius and some weak isolated nebulosities near the Coal Sac, Centauri and Normae. H photographs, a chart mapping the emission, and a list of identified emission regions are given. 相似文献
20.
On the basis of the erenkov line emission theory in the optically thick case, a new interpretation of intensity ratios H/H and H/H in broad-line radio-galaxies (BLRGs) is reported. Calculation shows that if the theoretical ratio H/H is just taken to be the mean observed value 0.21, equivalently, the parameterX(H)=3.0, then the expected ratio H/H=6.70 is almost the same as the observations. By comparing these values with the previous investigations of QSOs (X(H)=20.9), we conclude that the number density of neutral hydrogen gas in BLRGs is almost one order-of-magnitude smaller than that in the QSOs.Preliminary verification of the erenkov line emission has been obtained by Xuet al. (1981) in the laboratory. 相似文献