Alexander Mishev

Analysis of the ground level enhancement on 17 May 2012 using data from the global neutron monitor network

We have analyzed the data of the world neutron monitor network for the first ground level enhancement of solar cycle 24, the ground level enhancement (GLE) on 17 May 2012. A newly computed neutron monitor yield function and an inverse method are applied to estimate the energy spectrum, anisotropy axis direction, and pitch angle distribution of the high-energy solar particles in interplanetary space. The method includes the determination of the asymptotic viewing cones of neutron monitor stations through computations of trajectories of cosmic rays in a model magnetosphere. The cosmic ray particle trajectories are determined with the GEANT-based MAGNETOCOSMICS code using Tsyganenko 1989 and International Geomagnetic Reference Field models. Subsequent calculation of the neutron monitor responses with the model function is carried out, that represents an initial guess of the inverse problem. Derivation of the solar energetic particle characteristics is fulfilled by fitting the data of the global neutron monitor network using the Levenberg-Marquardt method over the nine-dimensional parameter space. The pitch angle distribution and rigidity spectrum of high-energy protons are obtained as function of time in the course of the GLE. The angular distribution appears quite complicated. It comprises a focused beam along the interplanetary magnetic field line from the Sun and a loss-cone feature around the opposite direction, possibly indicative of the particle transport in interplanetary magnetic field structures associated with previous coronal mass ejections.

Can we properly model the neutron monitor count rate

Neutron monitors provide continuous measurements of secondary nucleonic particles produced in the atmosphere by the primary cosmic rays and form the main tool to study the heliospheric modulation of cosmic rays. In order to study cosmic rays using the world network of neutron monitor and needs to be able to model the neutron monitor count rate. Earlier it was difficult because of the poorly known yield function, which has been essentially revisited recently. We have presented a verification of the new yield function of the standard neutron monitor (NM) using a recently released data on the direct in situ measurements of the galactic cosmic rays energy spectrum during 2006–2009 (the period of the record high cosmic ray flux) by Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics spaceborne spectrometer, and on NM latitude surveys performed during the period of 1994–2007, including periods of high solar activity. We found a very good agreement between the measured count rates of sea level NMs and the modeled ones in very different conditions: from low to high solar activity and from polar to tropical regions. This implies that the count rate of a sea level neutron monitor can be properly modeled in all conditions, using the new yield function.

Computations of cosmic ray propagation in the Earth's atmosphere, towards a GLE analysis

Computation of solar energetic particles propagation in the magnetosphere and atmosphere of the Earth is very important for ground level enhancement analysis. Detailed simulations of solar energetic particles events starting from asymptotic direction computation and NM detector response make it possible to build a strategy for inverse problem solution i.e. obtaining the characteristics of solar energetic particles on the basis on ground measurements. In this study a simulation of cosmic ray atmospheric cascade is carried out with PLANETOCOSMICS code. Energy spectra of secondary particles, namely neutrons and protons are obtained at various altitudes in the rigidity range of 0.7 GV to 1 TV of primary particles. Considering updated results for NM-64 detection efficiency the specific yield function for the standard neutron monitor is obtained for vertically and obliquely incident primary particles. The obtained results and applications are discussed.

Heliospheric modulation of cosmic rays during the neutron monitor era: Calibration using PAMELA data for 2006–2010

A new reconstruction of the heliospheric modulation potential for galactic cosmic rays is presented for the neutron monitor era, since 1951. The new reconstruction is based on an updated methodology in comparison to previous reconstructions: (1) the use of the new-generation neutron monitor yield function, (2) the use of the new model of the local interstellar spectrum, employing in particular direct data from the distant missions, and (3) the calibration of the neutron monitor responses to direct measurements of the cosmic ray spectrum performed by the PAMELA space-borne spectrometer over 47 time intervals during 2006{2010. The reconstruction is based on data from six standard NM64-type neutron monitors (Apatity, Inuvik, Kergulen, Moscow, Newark and Oulu) since 1965, and two IGY-type ground-based detectors (Climax and Mt.Washington) for 1951-1964. The new reconstruction, along with the estimated uncertainties is tabulated in the paper. The presented series forms a benchmark record of the cosmic ray variability (in the energy range between 1-30 GeV) for the last 60 years, and can be used in long-term studies in the fields of solar, heliospheric and solar-terrestrial physics.

Erratum to: Analysis of the ground level enhancements on 14 July 2000 and on 13 December 2006 using neutron monitor data

On the basis of neutron monitor data, we estimate the energy spectrum, anisotropy axis direction, and pitch-angle distribution of solar energetic particles during two major ground-level enhancements (GLE 59 on 14 July 2000 and GLE 70 on 13 December 2006). For the analysis we used a newly computed neutron monitor yield function. The method consists of several consecutive steps: definition of the asymptotic viewing cones of neutron monitor stations considered for the data analysis by computing the cosmic ray particle propagation in a model magnetosphere with the MAGNETOCOSMICS code, computing the neutron monitor model responses, and deriving the solar energetic particle characteristics on the basis of inverse problem solution. The pitch-angle distribution and rigidity spectrum of high-energy protons are obtained as a function of time in the course of ground-level enhancements. A comparison with previously reported results is performed and reasonable agreement is achieved. A discussion of the obtained results is included.

Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions

New consistent and precise computations of the production of five cosmogenic radioisotopes, 7Be, 10Be, 14C, 22Na, and 36Cl, in the Earths atmosphere by cosmic rays are presented in the form of tabulated yield functions. For the first time, a detailed set of the altitude profiles of the production functions is provided which makes it possible to apply the results directly as input for atmospheric transport models. Good agreement with most of the earlier published works for columnar and global isotopic production rates is shown. Altitude profiles of the production are important, in particular for such tasks as studies of strong solar particle events in the past, precise reconstructions of solar activity on long-term scale, tracing air mass dynamics using cosmogenic radioisotopes, etc. As an example, computations of the 10Be deposition flux in the polar region are shown for the last decades and also for a period around 780 A.D. and confronted with the actual measurements in Greenland and Antarctic ice cores.

Experimental study and Monte Carlo modeling of the Cherenkov effect

Abstract Studies realised at the Institute for Nuclear Research and Nuclear Energy (INRNE) particularly in cosmic ray detection and construction of Muonic Cherenkov Telescope at the South West University “Neofit Rilski” Blagoevgrad show the need to develop a theoretical model based on observed phenomena and to refinement of this for detection system optimisation. The Cherenkov effect was introduced in EGS4 code system. The first simulations realised in collaboration between the french and the bulgarian team were consecrated to different geometries of water tank in total reflection. An additional modeling of photons mean trajectory and the mean number of reflections in the tank were made. This simple model was compared with experimental data realised with 60Co gamma source, the telescope and the most efficient water tank. A trajectory simulation of Cherenkov photons in water tank was made. An efficiency estimation of the detector registration was calculated. The atmospheric model was introduced in EGS4 code and a comparison between CORSIKA5.62 and EGS4 codes was made.

Simulations and measurements of Atmospheric Cherenkov light, neutron and muon cosmic ray flux at Basic Environmental Observatory Moussala for space weather studies

The existing devices connected with space weather studies at Basic Environmental Observatory Moussala are described, especially the experiments with space weather and astroparticle studies. The recent results from simulations and measurements of the secondary cosmic ray using atmospheric Cherenkov light telescope are presented and the possibility to study the atmospheric transparency is discussed. The final design of neutron flux meter based on gas-filled SNM-15 detectors is described as well several preliminary experimental and Monte Carlo results. The developed muon telescope based on water Cherenkov detectors is also presented. Several recent measurements are shown. The scientific potential of existing is discussed, especially the connection between cosmic ray measurements and the environmental parameters, precisely atmospheric ones.

Model CRAC:EPII for atmospheric ionization due to precipitating electrons: Yield function and applications

A new model of the family of CRAC models, CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization), is presented. The model calculates atmospheric ionization induced by precipitating electrons and uses the formalism of ionization yield functions. The CRAC:EPII model is based on a full Monte Carlo simulation of electron propagation and interaction with the air molecules. It explicitly considers various physical processes, namely, pair production, Compton scattering, generation of bremsstrahlung high-energy photons, photoionization, annihilation of positrons, and multiple scattering. The simulations were performed using GEANT 4 simulation tool PLANETOCOSMICS with NRLMSISE 00 atmospheric model. The CRAC:EPII model is applicable to the entire atmosphere. The results from the simulations are given as look-up table representing the ionization yield function. The table allows one to compute ionization due to precipitating electrons for a given altitude and location considering a given electron spectrum. Application of the model for computation of ion production during electron precipitation events using spectra from balloon-borne measurements is presented.

GAMMA RAYS STUDIES BASED ON ATMOSPHERIC CHERENKOV TECHNIQUE AT HIGH MOUNTAIN ALTITUDE

We present a new method for ground based gamma ray astronomy based only on atmospheric Cherenkov light flux analysis. The Cherenkov light flux densities in extensive air showers initiated by different primaries are simulated in the energy range 100 GeV – 100 PeV for different primaries using the CORSIKA 6.003 code at (536 g/cm2). An approximation of lateral distribution of Cherenkov light flux densities in EAS is obtained using a nonlinear fit such as Breit-Wigner. The simulated and reconstructed events are compared and the accuracy in energy and primary mass reconstruction are obtained.