Gamma-rays from Active Galactic Nuclei: Emission processes and particle acceleration

It is argued that the high-energy X-ray and -ray emission from flaring blazars is beamed radiation from the relativistic jet supporting the relativistic beaming hypothesis and the unified scenario for AGNs. Most probably the high-energy emission results from inverse Compton scattering by relativistic electrons and positrons in the jet of radiation originating external to the jet plus pair annihilation radiation from the jet. Future positive TeV detections of EGRET AGN sources will be decisive to identify the prominent target photon radiation field. Direct -ray production by energetic hadrons is not important for the flaring phase in -ray blazars, but the acceleration of energetic hadrons during the quiescent phase of AGNs is decisive as the source of secondary electrons and positrons through photo-pair and photo-pion production. Injection of ultrahigh energy secondary electrons and positrons into a stochastic quasilinear acceleration scheme during the quiescent AGN phase leads to cooling electron-positron distribution functions with a strong cut-off at low but relativistic energy that under certain local conditions may trigger a plasma instability that gives rise to an explosive event and the flaring -ray phase.     

Ionospheric differential error determination using ray tracing for a short baseline

Since the United States government discontinued Selective Availability (SA) on 1 May 2000, ionospheric effects have been responsible for the largest errors in GPS systems. The standard Differential GPS (DGPS) method is incapable of completely eliminating the ionospheric error. This paper describes a new approach to determine the differential ionospheric error between geographically distributed receiver stations. The ray paths of GPS signals were simulated using a modified Jones 3D ray tracing programme that includes the effect of the geomagnetic field. A Nelder–Mead optimisation algorithm was embedded in the program to precisely determine the satellite-to-station path. A realistic ionospheric model is essential for accurate ray tracing results and for estimates of differential error that are accurate on sub-centimetre scales. Here, the ionospheric model used in the ray tracing programme was developed by fitting realistic ionosphere profiles with a number of exponential functions. Results were compared to the theoretical approach. Results show that the differential delay is about 1–5 cm at low elevation angles for a short baseline of 10 km, as reported in other literature. This delay is often neglected in DGPS application. The differential delay also shows a pattern similar to that predicted by the Klobuchar model. The method proposed here can be used to improve future GPS applications.     

The investigation of powerful solar flares characteristics by analysis of excited states of C and various neutrons capture lines

Accelerated energetic particles in solar flares produced nuclear γ-lines in interactions with ambient solar atmosphere. Analysis of intensity of ratios between various γ-lines allows us to make estimations of abundance of elements, parameters of surrounding media and other solar characteristics. In this article we discuss the flux ratio between two lines from excited states of ¹²C (f_15.11/f_4.44) and our results of preliminary calculation of intensity ratio between two neutron capture lines at ³He and ¹H (f_20.58/f_2.223). In particular we consider the opportunity to obtain n(³He)/n(¹H) ratio during solar flares and using high-energy gamma-emission studying, based on the satellite data. Possible interpretation of spectral features observed during the January 20, 2005 solar flare is discussed. Preliminary analysis of energy spectrum in the band of 2–21 MeV gives n(³He)/n(¹H) ∼ 8 × 10⁻⁴ for January 20, 2005 solar flare.     

A method to test HF ray tracing algorithm in the ionosphere by means of the virtual time delay

It is well known that a 3D ray tracing algorithm furnishes the ray’s coordinates, the three components of the wave vector and the calculated group time delay of the wave along the path. The latter quantity can be compared with the measured group time delay to check the performance of the algorithm. Simulating a perfect reflector at an altitude equal to the virtual height of reflection, the virtual time delay is assumed as a real time delay. For a monotonic electronic density profile we find a very small relative difference between the calculated and the virtual delay for both analytic and numerical 3D electronic density models.     

Status of the GAMMA-400 project

The preliminary design of the new space gamma-ray telescope GAMMA-400 for the energy range 100 MeV–3 TeV is presented. The angular resolution of the instrument, 1–2° at E_γ ∼ 100 MeV and ∼0.01° at E_γ > 100 GeV, its energy resolution ∼1% at E_γ > 100 GeV, and the proton rejection factor ∼10⁶ are optimized to address a broad range of science topics, such as search for signatures of dark matter, studies of Galactic and extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission, gamma-ray bursts, as well as high-precision measurements of spectra of cosmic-ray electrons, positrons, and nuclei.     

Gamma-hadron separation at high energies in view of recent cross section measurements

Recent measurements of the cross section for hadron photoproduction at HERA are reviewed and their importance for gamma ray astronomy is outlined. Various methods of distinguishing gamma and hadron primaries among cosmic rays in the air shower range are then discussed in view of our (insufficient) knowledge of the relevant hadron hadron cross sections. Theoretical model calculations indicate that the fraction of proton primaries mimicking gamma rays may be as high as one in a thousand.     

Research on the disturbance of ballistic missile to ionosphere by using 3D ray tracing method

This study uses the 3D ray tracing to analyse ionospheric disturbance generated by a ballistic missile plume (which was simulated in our previous work). Ray tracing results show that the 6 MHz radio waves are completely reflected by the ionosphere and cannot reach the ionospheric disturbance zone. The 8 MHz radio waves partially penetrate the ionospheric disturbance zone, producing a focusing effect. Most of the 10 MHz radio waves pass through the ionosphere and the disturbance zone. The focusing effect and focus height are reduced. In the height range 65̃400 km, the ray absorption loss of reflection is greater than the transmitted ray. When the ray is reflected multiple times in the cavity formed by the plume, ray absorption loss greatly increases.     

星敏感器光学系统的热/结构/光分析

星敏感器是高精度的航天器姿态测量器件,其性能受太空温度环境的影响。运用有限元法和光线追迹法,建立星敏感器光学系统的热/结构/光分析模型,研究光学系统温度分布与星敏感器测量误差的关系,得到了算例光学系统在温度均匀分布条件下的温度变化以及轴向温度梯度变化、侧向温度梯度变化与星敏感器测量误差的关系曲线;给出了算例光学系统热误差小于角秒量级的温度条件:均匀温度分布条件下温度变化量≤10℃、轴向温度梯度≤0.1310℃/mm、侧向温度梯度≤0.0325℃/mm,为高精度星敏感器光学系统热控制提供科学的依据。