Low energy γ-ray events in imaging Čerenkov telescope arrays

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.     

Radiation and energy loss by monopole in cosmic plasma

Radiation and energy loss by monopole in cosmic plasma are investigated in detail. The general formulae for monopole radiation are derived; the erenkov power and spectra radiation differing from ones of charged particles are found; and its energy loss in cosmic plasma and metal is obtained. It is pointed out that it is possible to examine monopole in virtue of the erenkov radiation in ordinary medium.     

Čerenkov radiation within the Earth's upper atmosphere

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.     

Gamma Ray and Hadron generated Čerenkov Photon Spectra at Various Observation Altitudes

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.     

Čerenkov radiation in anisotropic plasmas

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.     

Possible influence of cosmic ray Čerenkov photons on infrared interferometric search for non-solar planets

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.     

Spontaneous and induced Čerenkov emission in a turbulent medium

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.     

Rediscussion of balmer decrement of broad-line radio-galaxies

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.     

Гидромагнитное Излучение Межпланетной Плазмы

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Optical Observations of the Nearby Isolated Pulsar PSR 0656+14 at the SAO 6-meter Telescope.

BVR data for the middle-aged radio pulsar PSR 0656+14 obtained on January 20-21, 1996 at the 6-m telescope of the Special Astrophysical Observatory are presented. The brightness of a star-like object coincident with the position of the VLA radio source in the Cousins B filter is B 25.1, with eff = 4448Å, adjacent to the HST F130LP long-pass filter. The relatively large V and R fluxes (3 or > 10-30 ergs cm-2 s-2 Hz-1) provide evidence that the optical emission of this pulsar is non-thermal up to 6600 Å. Most probably, in the UV-optical (BVR) spectral range, a power-law spectrum is super-imposed on the thermal-like emission of the neutron star surface, which could be related to the mechanism of the pulsar activity itself.     

Observation of MKN 501 at gamma-ray energies

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.     

Перенос поляризации излучения В магнитоактивной космической плазме

u , . , .. (1.10), (1.2) ( (1.2)) . (1964) . (1.10), , , , (1.13). , , S _iq ,R _iglm ,K _iqlm (1.10) . , . . , (1.3), (2.3); (2.8)–(2.10). , , , , z (2.20), .. , , (. (2.15)). (K _{e, 0} ) . ^S , ( (2.24)). (2.24a) ^S ±/4. , , (K _{e, o}<0). L, — , , ; , . .     

Estimates of the γ-ray flux from Sagittarius A

Analysis of the anisotropy of the -ray background observed by Clarket al. (1968) has lead to the suggestion that part of the anisotropy be due to a source at the Galactic Centre. The complex structure of radio and infrared emission of the region of Sgr A is considered. The -ray flux arising from Compton scattering and ₀ decay is calculated. For a value of the magnetic field H10^–4 Gauss, corresponding to equipartition, the -ray flux above 100 MeV at Earth from the Sgr A source is expected to lie between 10^–6 and 10^–5 gamma/cm² sec. Such a source should be detectable in the near future.     

Абсолютная система высот в краевой зоне луны по наблениям покрытий звэзд

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О ФОрРИРОВНИИИ диаграммы излучения пульсаров

, v ₀c (c — ). , , . 1919, . ( ) 0532. , .     

Horizontal-branch star models

Evolutionary tracks of 0.9M , 0.7M and 0.6M models for Population II stars have been computed in the post-red giant phase. The stars are initially composed of a helium core containing a mass fraction equal to 0.9 and of a hydrogen-rich envelope. They represent hypothetical remnants of stars after substantial mass loss in previous evolutionary phases or/and at the helium flash.u 0,9M , 0,7M 0,6M . , 90% , . , .Riassunto È stata calcolata per modelli di stelle di 0,9M , 0,7M e 0,6M di Popolazione II l'evoluzione successiva allo stadio di gigante rossa. Inizialmente i modelli constano di un nucleo di elio contenente il 90% della massa totale e di un inviluppo idrogenico. Essi possono interpretarsi come i resti di stelle che abbiano perso una frazione di massa considerevole in fasi evolutive precedenti, o all'innesco violento dell'elio al centro.     

On the stability of equilibria of Hamiltonian systems near the main resonances

The equilibrium point O of an autonomous Hamiltonian system of two degrees of freedom is considered for small-oscillation frequencies related as ₂=2₁+. If under the precise resonance (=0) the equilibrium is unstable, the inner diameter () of the domain of stability containing the point O is estimated. It is shown that for the normalized variables ()/b where b is the corresponding resonance coefficient. The estimates () for other main resonances are reported.     

Космическое черенковское излучение

, . N/E, E _r, (E _r)=1. , (, ) . .     

Поле излучения в полубесконечной атмосфере, содержащей источники энергии

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Energy spectra of cosmic ray nuclei: 4≤Z≤26 and 0.3≤E≤2 GeV amu−1

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.