共查询到20条相似文献，搜索用时 46 毫秒
1.
I. Lerche 《Astrophysics and Space Science》1970,8(1):29-49
It is shown that the presence of spatially random fluctuations in refractive index, about a mean exceeding unity, influences the power output of erenkov waves emitted by a charged particle in several ways.(1) The frequency spectrum of the spontaneous emission is altered by the fluctuations. (2) There is an induced erenkov emission, due to the interaction of the spontaneous field with the random refractive index variations. This induced field can, in certain frequency bands, be as large as the spontaneous field. And it also contains a backscattered component which propagates in theopposite direction to the particle. (3) The conditions for emission of the erenkov waves, be they spontaneous or induced, depend critically on both the mean refractive index, the particle velocity, the intensity and correlation length of the fluctuations. And the dependence is sensitive to the precise functional form of the two-point correlation function.Instruments detect the optical erenkov emission produced by cosmic ray particles penetrating the Earth's atmosphere (below about 5 km). Also gas erenkov counters are triggered by the passage of highly energetic particles through the gas. Since both the Earth's lower atmosphere and the gas counters contain turbulent fluctuations, the present calculation is of some interest in connection with particle energy loss mechanisms in turbulent media and the basic structure of such media. 相似文献
2.
A brief review of erenkov radiation within the upper atmospheric plasma has been presented. Different attempts in this context are systematically discussed. The results of analysis about the nature and characteristics of VLF hisses in terms of incoherent erenkov radiation are given in a concise manner. The occurrence of resonance cone has also been reported. 相似文献
3.
Following our series of works on anisotropic radiation, we analyze the erenkov condition in magnetized plasmas in this paper. We have discovered that the usual erenkov condition cos =1/n isnot satisfied at a far field point in anisotropic media, implying that when a charge is moving in a magnetized plasma, a linear shock wave front does not form. Thus we can calculate the power received at a far field per unit time in such a medium — this quantity could not be evaluated according to previous theory. Numerical examples are presented to show various relevant characteristics of erenkov radiation in model plasmas. 相似文献
4.
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
5.
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
6.
M. A. Rahman P. N. Bhat B. S. Acharya V. R. Chitnis P. Majumdar P. R. Vishwanath 《Experimental Astronomy》2001,11(2):113-131
We study the propagation of erenkov photons generated by Very HighEnergy -rays and hadrons in the atmosphere. The photon productionheight distributions are estimated from semi-empirical methods andcompared with those derived by standard simulation techniques. Incidentspectra at various observation altitudes are then derived after applyingwavelength dependent corrections due to photon attenuation in theatmosphere during the propagation of photons from the height of productionto the height of observation. These are generated both for -ray and hadron primaries of various energies. The derivedproduction height distributions agree very well with those generated bythe simulation package `CORSIKA' at all energies and for both -ray and proton primaries. The incident photon spectra are found to beboth altitude and primary energy dependent. The peak ofthe incident spectrum shifts towards the shorter wavelength withincreasing altitude of observation for a given primary. Also the peak ofthe photon spectrum shifts towards the shorter wavelength withincreasing energy of the primary at a given altitude. The fraction of the UVcomponent in the incident erenkov spectrum is estimated both for-ray and hadronic primaries at various observation altitudes andenergies. Hadron generated erenkov spectra are marginally richer in UVlight and the difference increases slightly at higher altitudes. The fraction of the UV to the visible light in the erenkov spectrum could be a usefulparameter to separate -rays from cosmic ray background only if onecan measure this fraction very accurately. 相似文献
7.
I. Lerche 《Earth, Moon, and Planets》1980,22(4):435-437
It is shown that the pervasive cosmic-ray protons in the vicinity of the Earth would produce infrared photons by erenkov radiation in the material walls, and mirrors, of an orbiting infrared interferometer designed to search for non-solar planets. The flux of such photons is at least comparable to the zodiacal infrared background radiation. It is found that for the worst possible conditions a minimum time of about six weeks is indicated for planetary detection using a fourth-harmonic noise analysis. It is suggested that direct laboratory measurement of a simulated cosmic-ray-induced erenkov flux be undertaken to settle the question of the background contaminant produced by this effect. 相似文献
8.
I. Lerche 《Astrophysics and Space Science》1970,8(2):185-203
Coherent electromagnetic erenkov radiation is produced by cosmic ray air showers passing through the atmosphere. This radiation is detected by radio telescopes. We demonstrate here that the effect of random spatial fluctuations in the refractive index of air, about a mean exceeding unity, causes the airshower to emit not only the spontaneous coherent radio emission described elsewhere by Kahn and Lerche, but also an induced radiation field which can exceed the spontaneous field in certain frequency bands. Further the conditions for emission of the coherent radio erenkov radiation are altered by the presence of the refractive index fluctuations. And the Earth's magnetic field gives rise to the dominant term in the far-field radiation, be it spontaneous or induced, since it causes a systematic separation of electrons and positrons in the shower which, for parameters currently acceptable for air showers, is the major factor in determining the far-field radiation pattern. Also we suggest that the coherent 500 Mc/sec radiation seen from occasional showers is probably a reflection of an atmospheric correlation length of order 15 cm at the time the shower passes through the atmosphere. 相似文献
9.
M. E. Gedalin J. G. Lominadze L. Stenflo V. N. Tsytovich 《Astrophysics and Space Science》1985,108(2):393-400
Wave conversion mechanisms causing large-frequency shifts are considered for an electron-positron plasma in a strong magnetic field. In particular, we discuss the effects of the nonlinear erenkov as well as the cyclotron resonances in order to associate pulsar radio-emissions with our present model for nonlinear conversion of high-frequency radiation into the low-frequency region. 相似文献
10.
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
11.
G. Lessner 《Astrophysics and Space Science》1984,100(1-2):359-367
It is shown that in the radiation era of the Universe spatial temperature fluctuations (T/T)<10–5 in the cosmic plasma lead to huge changes of the density up to (/)104. This effect results from the fact that the cosmic plasma in the radiation era can be considered as a general relativistic Boltzmann gas which is found in the very vincinity of equilibrium. 相似文献
12.
Two wide-angle photomultiplier systems were simultaneously operated over a baseline of nearly 30 km in a search for cosmic optical bursts of fractional microsecond time-scale. In 74 hours of overlapping observation, one event was recorded coincident to 1 ms as against the corresponding accidental coincidence value of 0.14 from erenkov light pulses from unrelated cosmic ray showers. The possible cosmic origin of this event, including that from primordial black-hole explosions, is discussed and the corresponding upper limits derived. 相似文献
13.
Energy spectra of cosmic ray nuclei in the charge range 5Z26 have been derived from the response of an acrylic plastic erenkov detector. Data were obtained using a balloon-borne detector and cover the energy range 320E2200 MeV amu–1. Spectra are derived from a formal deconvolution using the method of Lezniak (1975). Relative spectra of different elements are compared by observing the charge ratios. Secondary-primary ratios are observed to decrease with increasing energy, consistent with the effect previously observed at higher energy. Primary-to-primary ratios are constant for 6Z10 and 14Z26 but vary for 10Z14. This data is found to be consistent with existing data, where comparable, and lends strong support to the idea of two separate source populations contributing to the cosmic ray composition.Work supported by University of Maryland Grant NGR 21-002-316. 相似文献
14.
D. J. Buckley M. C. Dorrington P. J. Edwards T. J. L. McComb S. P. Tummey K. E. Turver 《Experimental Astronomy》1999,9(4):237-249
A technique for detecting the presence of cloud in the field of view of an atmospheric erenkov telescope using a mid infra red radiometer is described. Models for the radiative emission from clear and cloudy skies are tested and found to represent the measurements. 相似文献
15.
R. N. Bracewell 《Earth, Moon, and Planets》1984,30(1):75-77
Infrared emission from a planet at a very small angular separation from its star offers the possibility for detection by interferometry from space. However it has been suggested that attention should be paid to interference produced by the infrared radiation that would be generated within the space package by cosmic ray protons. Quantitative examination reveals that both the primary erenkov flux and the secondary infrared emission from erenkov heating are negligible. 相似文献
16.
В. М. Чаругин 《Astrophysics and Space Science》1975,37(2):441-447
, . N/E, E
r, (E
r)=1. , (, ) . . 相似文献
17.
0–2 ( ). . . . 相似文献
18.
19.
The currently available infrared data on scattered light from the dust comae of ernis and Bowell set stringent upper limits to the contribution of icy grains. For Comet ernis the data is consistent with only a 10% mass fraction of water-ice included within silicate-organic-carbon grains of scale radius 15 microns, while for Comet Bowell there is no evidence for any ice component. A coma of small (10–100m) organic grains containing a fraction of OH-bearing molecules that evaporate over weeks at 5 AU and leave an absorptive carbonaceous grain residue is the simplest model for Comet Bowell. 相似文献
20.
A. A. Stepanian B. M. Vladimirsky Yu. I. Neshpor V. P. Fomin 《Astrophysics and Space Science》1975,38(2):267-282
The results of the observations to search gamma-ray sources with the energy greater than 2×1012 eV, which were made in Crimean Astrophysical Observatory during the years 1969–73 are presented. A technique of the detection of the EAS Cerenkov flashes was used.The quality of the data obtained is analysed. The criteria for the selection of the data free from meteorological variations are considered.It was shown that two objects, namely, Cyg X-3 and Cas -1, may be the sources of high-energy gamma quanta. It is probable that the object with the coordinates =05h15m, =+1° is the source of gamma-rays as well. An unidentified object Cas -1 is variable: gamma-ray flux was observed twice — in Sepember–October 1971 and in December 1972. It is possible that the flux from Cyg X-3 has a period of 4.8 hr.
I I , I I , - >2.1012 . I . I , I I, I ., - -1 Cyg -3- -I . , =0515 ·=+1° -.I -1 I: I J I- - 1971 1972 . Cyg -3, , - T=4.8 .相似文献