arXiv subjects

Gohar Rastegarzadeh

Publications and source records attributed to Gohar Rastegarzadeh.

3 recordsLinked to original sources

arXiv2026

Energy estimation of cosmic rays by air shower radio signals

We present a method for reconstructing the primary energy of cosmic ray air showers using radio emission. The approach is based on CoREAS simulations performed for both the SURA experiment and a dense reference array of antennas. By comparing the simulated electric field intensity from the dense array with that obtained for the SURA configuration, we derive a scale factor (Ci j). This scale factor exhibits a correlation with the primary energy, decreasing as energy increases. Unlike previous approaches employed by various experiments, our technique shows limited sensitivity to the shower core location. Even for the farthest core positions allowed by the array, the scale factor remains effectively independent of the core location. We also examined the accuracy and reliability of the reconstruction method. Finally, we reconstructed the primary energy of cosmic rays using our method with a maximum error of about 11% in our simulation tests.

astro-ph.IM↗

arXiv2019

Linear Analysis of the Nonaxisymmetric Secular Gravitational Instability

In protoplanetary discs (PPDs) consisting of gas and dust particles, fluid instabilities induced by the drag force, including secular gravitational instability (SGI) can facilitate planet formation. Although SGI subject to the axisymmetric perturbations was originally studied in the absence of gas feedback and it then generalized using a two-fluid approach, the fate of the nonaxisymmetric SGI, in either case, is an unexplored problem. We present a linear perturbation analysis of the nonaxisymmetric SGI in a PPD by implementing a two-fluid model. We explore the growth of the local, nonaxisymmetric perturbations using a set of linearized perturbation equations in a sheared frame. The nonaxisymmetric perturbations display significant growth during a finite time interval even when the system is stable against the axisymmetric perturbations. Furthermore, the surface density perturbations do not show continuous growth but are temporally amplified. We also study cases where the dust component undergoes amplification whereas the gas component remains stable. The amplitude amplification, however, strongly depends on the model parameters. In the minimum mass solar nebula (MMSN), for instance, the dust fluid amplification at the radial distance 100 au occurs when the Stokes number is about unity. But the amplification factor reduces as the dust and gas coupling becomes weaker. Furthermore, perturbations with a larger azimuthal wavelength exhibit a larger amplification factor.

astro-ph.GA↗

arXiv2017

Estimating primary energy of cosmic rays by calculating secondary particles density in optimum distance from shower core

Optimum distance (Ropt) is a distance from the shower core in which the density calculated by lateral distribution function, has its minimum uncertainty. In this paper, Using CORSIKA code, proton, carbon and iron primary in the energy range between 1013 - 3*1015eV are simulated to find Ropt for Alborz-I array located at an altitude of 1200 m above sea level. It is shown that Ropt is approximately independent of characteristics of primary particle and it is only dependent to array configuration. Dependency of Ropt on layout and detector spacing for 20 Alborz-I array detectors, are studied. It is shown that the Alborz-I array layout and its detector spacing result into the best (minimum uncertainty) Ropt for its number of detectors. In this work Ropt for Alborz-I array is obtained about 9 m. In addition, it is shown that, by finding dependency of primary energy to density in optimum distance, energy of primary particle can be estimated well. An energy estimation function is suggested and the function is examined by another set of simulated showers.

astro-ph.HE↗