Data from a small air shower array were used to examine the cosmic ray shadow of the Moon at energies more than 100
TeV. A simple technique has been used for the analysis of this data. In this ...technique the number of EAS events with arrival directions falling in error circles centered about the moving moon is compared to the mean number of events falling in error circles with centers randomly chosen in the sky. For any assumed angular radius of the error circle the deficit in EAS event count in the direction of moon which is a moon-related effect is interpreted as the shadow of the moon. A simple theoretical model has been developed to relate the mean number of EAS events,
N
sky
, to the angular radius of the error circle and has been applied to the counts from the moon’s direction in order to extract the physical parameters of the shadow of the moon. The technique and the theoretical model has been used on
1.7
×
10
5
EAS events recorded by a small air shower array.
Analysis of an extensive air shower (EAS) detected by surface arrays highly depends on the determination of core locations. Here we present a new method to find the core location of an EAS that, ...unlike the common methods, does not depend on the lateral distribution function and uses arrival times of secondary particles. This method improves the accuracy of finding the core location of a low-energy EAS in the internal parts of an array, in comparison with common methods.
► A new method for finding an initial trial core location of an EAS and reconstructing its geometry has been introduced. ► The method is independent of lateral distribution function. ► It is not ...based on density-sensitive detectors. ► For the assumed array of the paper, the arrival direction has improved greatly in comparison with the plane front approximation.
The most important goal of studying an extensive air shower is to find the energy, mass and arrival direction of its primary cosmic ray. In order to find these parameters, the core position and arrival direction of the shower should be determined. In this paper, a new method for finding core location has been introduced that utilizes trigger time information of particle detectors. We have also developed a simple technique to reconstruct the arrival direction. Our method is not based upon density-sensitive detectors which are sensitive to the number of crossing particles and is also independent of lateral distribution models. This model has been developed and examined by the analysis of simulated shower events generated by the CORSIKA package.
A new small array of Cherenkov detectors has been deployed in Tehran, 1200 m above sea level. This array contains four tanks of distilled water with a diameter of 64 cm and a height of 130 cm. The ...effective area of each tank is about 1382 cm2. They are used to detect air showers and to record the arrival time of the secondary particles. We have collected about 640 000 extensive air showers (EAS) in 8298 h of observation time from November 2006 to October 2007. The distribution of air showers in zenith and azimuth angles has been studied and a cosntheta distribution with n = 6.02 +/- 0.01 was obtained for the zenith angle distribution. An asymmetry has been observed in the azimuthal distribution of EAS of cosmic rays due to geomagnetic field. The first and second amplitudes of the asymmetry are AI = 0.183 +/- 0.001 and AII = 0.038 +/- 0.001. Since the recent results are in good agreement with our previous results of scintillation detectors, and tanks of distilled water are cheaper, we prefer to use them instead of scintillators in a future larger array. By simulation, we have improved the size of the detectors to yield the highest efficiency. The best dimensions for each tank with a photomultiplier tube in the center of its lid are 40 cm in diameter and 60 cm in height.
The effective compton cross section in a non-degenerate plasma
(
n
⪡
{
(
(
kT
/
c
)
2
+
2
mkT
)
/
h
2
}
3
/
2
) is investigated in a wide range of temperatures. The results show a decreasing behavior ...with temperatures especially for
kT
⪢
m
e
c
2
. The results may be important in phenomena like accretion discs or ultra-relativistic blast waves in GRB models, where the emitted radiation has to pass through a medium containing high-energy electrons.
It has been suggested that young pulsars, with ages less than a million years, are possible counterparts of some of the Galactic unidentified gamma-ray sources detected by the EGRET instrument ...on-board the Compton Gamma Ray Observatory. In this work, we compare different aspects of the EGRET unidentified (EUI) source distribution in the Galactic plane with those of the pulsar distribution. An EUI source Log N–Log S analysis is presented and compared with the Galactic radio pulsar Log N–Log S distribution. A number of systematic effects that could introduce errors to the EGRET Log N–Log S relation are discussed. A two-point angular correlation analysis of the EUI sources and Galactic pulsars is performed. We find that the global distribution properties of the plane EUI sources do not follow those of the young pulsar population. We conclude that even though a fraction of the EUI sources may have young pulsar counterparts, the majority of them follow a distribution that is similar to the molecular cloud distribution in nearby spiral arms.
We propose two models, based on the hadronic beam-cloud collision, for production of TeV γ-ray flares in blazars. In the first model, a change in bulk Lorentz factor of the jet of the Active Galactic ...Nucleus (AGN) produces the flare. In the second model we consider a two-stage mechanism for high-energy particle acceleration in the jet. This system produces a power law spectrum with two different power indices at low and high energies, which is more efficient than one-stage shock acceleration at high energies. Using this spectrum in a hadronic beam-cloud model for γ-ray emission of blazars, a variable TeV as well as a stable GeV γ-ray flux is predicted. The break energy in the spectrum, related to distance between the jet base and terminal shock or boundary layer thickness, is the parameter used to obtain TeV flares.
Ultra-high-energy ($E>100$ TeV) Extensive Air Showers (EASs) have been monitored for a period of five years (1997–2003), using a small array of scintillator detectors in Tehran, Iran. The data have ...been analyzed taking into account the dependence of source counts on zenith angle. During a calendar year different sources come into the field of view of the detector at varying zenith angles. Because of varying thickness of the overlaying atmosphere, the shower count rate is extremely dependent on zenith angle, which has been carefully analyzed over time (Bahrnanabadi et al. 2002, Exp. Astron., 13, 39). High energy gamma-ray sources from the EGRET third catalogue where observed and the data were analyzed using an excess method. Upper limits were obtained for a number of EGRET sources, including 6 AGNs or probably AGNs and 4 unidentified sources.
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