Ground-Based Gamma Ray Astronomy

This paper is the write-up of a rapporteur talk given by the author at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil, in 2013. It attempts to summarize results and developments in ground-based gamma-ray observations and instrumentation from among the ～300 submissions to the gamma-ray sessions of the meeting. Satellite observations and theoretical developments were covered by a companion rapporteur (Stawarz, L., 33rd ICRC, Rio de Janeiro, Brazil, Rapporteur talk: Space-based Gamma-Ray Astronomy, 2013). Any review of this nature is unavoidably subjective and incomplete. Nevertheless, the article should provide a useful status report for those seeking an overview of this exciting and fast-moving field.     

Gamma ray astronomy and search for antimatter in the universe

Gamma ray astronomy provides a powerful tool for searching antimatter in the universe; it probably provides the only means to determine, if the universe has baryon symmetry. Presently existing gamma-ray observations can be interpreted without postulating the existence of antimatter. However, the measurements are not precise enough to definitely exclude the possibility of its existence. The search for antimatter belongs to one of the main scientific objectives of the Gamma Ray Observatory GRO of NASA, which will be launched in 1990 by the Space Shuttle.     

Afterglow from GRB 070610/Swift J195509.6+261406: An explanation using the fireball model

GRB 070610, which is also named Swift J195509.6+261406, is a peculiar Galactic transient with significant variability on short timescales in both X-ray and optical light curves. One possible explanation is that GRB 070610/Swift J195509.6 + 261406 is a soft gamma-ray repeater (SGR) in our Galaxy. Here, we use the fireball model, which is usually recognized as the standard model of gamma-ray burst (GRB) afterglows, and the energy injection hypothesis to interpret the X-ray and optical afterglow light curves of GRB 070610/Swift J195509.6 + 261406. It is found that the model is generally consistent with observations.

     

Unveiling the secrets of gamma ray bursts

Gamma Ray Bursts are unpredictable and brief flashes of gamma rays that occur about once a day in random locations in the sky. Since gamma rays do not penetrate the Earth's atmosphere, they are detected by satellites, which automatically trigger ground-based telescopes for follow-up observations at longer wavelengths. In this introduction to Gamma Ray Bursts we review how building a multi-wavelength picture of these events has revealed that they are the most energetic explosions since the Big Bang and are connected with stellar deaths in other galaxies. However, in spite of exceptional observational and theoretical progress in the last 15 years, recent observations raise many questions which challenge our understanding of these elusive phenomena. Gamma Ray Bursts therefore remain one of the hottest topics in modern astrophysics.     

Gamma畸变的相位误差模型与Gamma标定技术

Gamma畸变是数字相移测量技术的主要误差源。以通用的均匀步长相移技术为对象,分析了Gamma畸变对相位计算的影响,建立了相位误差与谐波系数的关系模型,证明了各阶谐波系数在Gamma值影响下的递推公式,进而提出了基于离散傅里叶变换的Gamma标定技术。基于此Gamma标定值,通过Gamma预矫正降低相位误差。实验结果表明,标定的Gamma值在整个像平面具有较强的稳定性,Gamma矫正后使相位误差减小了77.5%,在曲面测量的结果中,水波纹明显得到抑制,曲面质量得以提高。     

Ray stability in weakly range-dependent sound channels

Ray stability is investigated in environments consisting of a range-independent background sound-speed profile on which a range-dependent perturbation is superimposed. Theoretical arguments suggest and numerical results confirm that ray stability is strongly influenced by the background sound speed profile. Ray instability is shown to increase with increasing magnitude of alpha(I)=(I/omega)d omega/dI, where 2pi/omega(I) is the range of a ray double loop and I is the ray action variable. This behavior is illustrated using internal-wave-induced scattering in deep ocean environments and rough surface scattering in upward refracting environments.     

Monte Carlo study of a high resolution gamma ray telescope used as a polarimeter

Recent results of computer modeling show how the UCLA-UTD High Resolution Gamma Ray Telescope could potentially be used to detect the polarization states of incoming gammas to learn more about the nature of their source. The High Resolution Gamma Ray Telescope is operated as a Compton telescope consisting of a Liquid Argon Converter, a Gas Drift Chamber and a Liquid Argon Calorimeter. Through slight modifications of the telescope, we show that it may be possible to ascertain the linear polarization states of the gamma rays if a large enough number of events can be analyzed.     

Cosmic Ray research in Armenia

Cosmic Ray research on Mt. Aragats began in 1934 with the measurements of East-West anisotropy by the group from Leningrad Physical-Technical Institute and Norair Kocharian from Yerevan State University. Stimulated by the results of their experiments, in 1942 Artem and Abraham Alikhanian brothers organized a scientific expedition to Aragats. Since that time physicists were studying Cosmic Ray fluxes on Mt. Aragats with various particle detectors: mass spectrometers, calorimeters, transition radiation detectors, and huge particle detector arrays registering protons and nuclei accelerated in most violent explosions in Galaxy. Latest activities at Mt. Aragats include Space Weather research with networks of particle detectors located in Armenia and abroad, and detectors of Space Education center in Yerevan.     

Ultra-high energy cosmic rays and prompt TeV gamma rays from gamma ray bursts

Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events observed up to energies ≳ 10²⁰ eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole.     

Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet

Ryde and Petrosian have pointed out that the rise phases of gamma-ray burst (GRB) pulses originate from the widths of the intrinsic pulses and their decay phases are determined by the curvature effect of the expanding fireball surface based on their simplified formula. In this paper we investigate in detail the issue based on the formula in Ref.[20], which is derived based on a model of highly symmetric expanding fireballs, where the Doppler effect is the key factor to be concerned about, and no terms are omitted in their derivation. Our analyses show that the decay phases of the observed pulses originate from the contributions from both the curvature effect of the expanding fireball and the two timescales of the local pulses, and the rise phases of the observed pulses only come from the two timescales of the local pulses. Associated with a local pulse with both rise and decay portions, the light curve of GRBs in the rise portion is expected to undergo a concave phase and then a convex one, whereas that in the decay portion is expected to evolve by an opposite process. And the ratio of the concave timescale to the convex one in the rise phase of the observed pulse linearly increases with the ratio of the rising timescale to the decay one of the local pulse ($r_{\rm rd}$), whereas the ratio of the convex timescale to the concave timescale in its decay phase linearly decreases with $r_{\rm rd}$. The two correlations are independent of the local pulse forms and the rest-frame radiation forms. But the different forms of local pulses and the different values of $r_{\rm rd}$ gives rise to the diversity of the light curve pulse shapes. We test a sample of 86 GRB pulses detected by the BATSE instrument on board the Compton Gamma Ray Observatory and find that the characteristics do exist in the light curve of GRBs.     

A free-electron laser generated gamma-ray beam for nuclear physics

The High Intensity Gamma Ray Source (HIγS), a collaborative project between TUNL and the Duke Free Electron Laser Laboratory, is described. An initial experiment and plans for a future research program are discussed briefly.     

Gamma detectors in explosives and narcotics detection systems

Gamma detectors based on BGO crystals were designed and developed at the Joint Institute for Nuclear Research. These detectors are used in explosives and narcotics detection systems. Key specifications and design features of the detectors are presented. A software temperature-compensation method that makes it possible to stabilize the gamma detector response and operate the detector in a temperature range from ?20 to 50°C is described.     

Dielectron widths of the Gamma(1S,2S,3S) resonances

We determine the dielectron widths of the Gamma(1S), Gamma(2S), and Gamma(3S) resonances with better than 2% precision by integrating the cross section of e+e- -->Gamma over the e+e- center-of-mass energy. Using e+e- energy scans of the Gamma resonances at the Cornell Electron Storage Ring and measuring Gamma production with the CLEO detector, we find dielectron widths of 1.252+/-0.004(sigma(stat))+/-0.019(sigma(syst)) keV, 0.581+/-0.004+/-0.009 keV, and 0.413+/-0.004+/-0.006 keV for the Gamma(1S), Gamma(2S), and Gamma(3S), respectively.     

Identifying time-clustering structures in the sequence of solar flare hard X-ray bursts

Time-clustering behavior in the sequence of solar flare hard X-ray bursts from April 1991 to May 2000 obtained from BATSE/GRO (Burst and Transient Source Experiment aboard the Compton Gamma Ray Observatory satellite) was investigated by using the Allan Factor statistics. The presence of different timescale regimes ranging from Poissonian to rather strong long-range correlated behaviors has been revealed.     

Dark matter annihilation in the Galactic Center as seen by the Fermi Gamma Ray Space Telescope

We analyze the first two years of data from the Fermi Gamma Ray Space Telescope from the direction of the inner 10° around the Galactic Center with the intention of constraining, or finding evidence of, annihilating dark matter. We find that the morphology and spectrum of the emission between 1.25° and 10° from the Galactic Center is well described by the processes of decaying pions produced in cosmic ray collisions with gas, and the inverse Compton scattering of cosmic ray electrons in both the disk and bulge of the Inner Galaxy, along with gamma rays from known points sources in the region. The observed spectrum and morphology of the emission within approximately 1.25° (∼175 parsecs) of the Galactic Center, in contrast, departs from the expectations for by these processes. Instead, we find an additional component of gamma ray emission that is highly concentrated around the Galactic Center. The observed morphology of this component is consistent with that predicted from annihilating dark matter with a cusped (and possibly adiabatically contracted) halo distribution (ρ∝r−γ$\rho \propto r^{-\gamma }$, with γ=1.18$\gamma =1.18$ to 1.33). The observed spectrum of this component, which peaks at energies between 1–4 GeV (in E²$E^2$ units), can be well fit by a 7–10 GeV dark matter particle annihilating primarily to tau leptons with a cross section in the range of 〈σv〉=4.6×¹⁰⁻²⁷$〈\sigma v〉=4.6\times {10}^{-27}$ to 5.3×¹⁰⁻²⁶ cm³/s$5.3\times {10}^{-26}{\text{cm}}^3/\text{s}$, depending on how the dark matter distribution is normalized. We also discuss other sources for this emission, including the possibility that much of it originates from the Milky Way?s supermassive black hole.     

A new method for high-energy pulsed Gamma measurement within intense background x-rays

The accelerator-generating 6.13~MeV pulsed Gamma by ¹⁹F(p, αγ )¹⁶⁰ reaction usually synchronizes with an intense bremsstrahlung x-ray which has a maximum energy of 1~MeV. This paper proposes a new method, named the scattering and absorbing method, to diagnose the 6.13~MeV Gamma. This method includes two parts: the detector and a scatterer placed in front of the detector. The detector converts the Gamma to electrons and then collects the electrons by a scintillator. In order to restrain the interference of the low-energy background, the scintillator collects the electrons at a small angle. The scintillator is wrapped with electro-absorbing material to absorb the low-energy electrons generated by background x-rays. The theoretical sensitivity ratio of 6.13~MeV Gamma to 1~MeV x-rays is greater than 150. The scatterer is a pretreatment tool to scatter some background x-rays away from the radial beam before they enter the detector. By varying the length, the scatterer can reduce the background x-rays to an acceptable level for the detector.     

A comparison of Gamma and Gaussian dynamic convolution models of the fMRI BOLD response

Blood oxygenation level-dependent (BOLD) contrast-based functional magnetic resonance imaging (fMRI) has been widely utilized to detect brain neural activities and great efforts are now stressed on the hemodynamic processes of different brain regions activated by a stimulus. The focus of this paper is the comparison of Gamma and Gaussian dynamic convolution models of the fMRI BOLD response. The convolutions are between the perfusion function of the neural response to a stimulus and a Gaussian or Gamma function. The parameters of the two models are estimated by a nonlinear least-squares optimal algorithm for the fMRI data of eight subjects collected in a visual stimulus experiment. The results show that the Gaussian model is better than the Gamma model in fitting the data. The model parameters are different in the left and right occipital regions, which indicate that the dynamic processes seem different in various cerebral functional regions.     

来自γ暴的甚高能γ射线

以膨胀火球模型解释来自γ暴的甚高能γ射线,其中考虑了高能γ射线产生效率,相对论效应以及宇宙背景辐射等因素,计算表明,大于10GeV的γ射线的喷射可能在火球膨胀开始后约10^－5s发生,其到达地面时的通量可达10^－4—10^－6cm^－2.     

用大气荧光观测超高能宇宙线的τ中微子望远镜(CRTNT)性能研究

讨论了测量超高能宇宙线的τ中微子望远镜(CRTNT)的性能. 利用Monte Carlo方法对探测器作了详细的模拟, 并研究了探测器以一个塔形主探测器和两个高视角辅探测器协同触发的布局, 以及对大气簇射作立体观测时的物理性能. 计算了当能量高于10¹⁷eV时, 探测器的有效面积. 用于第2个膝区物理研究时事例率估计可达20k个/年. 还估算了与其他探测器交叉定标的事例率. 比较和优化了探测器的不同几何布局.     

On the 40th anniversary of the journal X‐Ray Spectrometry

This journal, X‐Ray Spectrometry, celebrates its 40th anniversary this year. The state of the publications on X‐ray spectral analysis from 1972 onward is considered. The distribution of materials over countries is presented, as published in X‐Ray Spectrometry for 40 years, in 5‐year time intervals: 1972–1976, 1977–1981, and so on. The participation of Russian scientists contributing to the publications in this journal is discussed. Copyright © 2012 John Wiley & Sons, Ltd.