用羊八井ASγ实验数据寻找TeV能区的γ射线暴

γ射线暴的TeV能区辐射对研究其起源、辐射机制等是非常重要的.利用西藏羊八井ASγ实验三期阵列的重建数据,通过在给定的小天区和时间间隔内寻找较高显著性事例团的方法对TeV能区的γ射线暴进行了寻找,在计算过程中采用“等天顶角法”来估计背景.工作中采用了两种途径来寻找γ射线暴,一种是与卫星γ射线暴的符合寻找,另一种是全天区独立寻找.结果发现少量事例团对背景有明显超出,考虑试验次数后,其超出还不足以认定为γ射线暴.通过Monte Carlo模拟,给出了在95%置信水平下,到达大气顶部流强上限的估计值为3.32×10^-9—1.24×10^-7 cm^-2s^-1. 关键词： γ射线暴 TeV能区 ASγ实验 宇宙射线     

Atmospheric gamma rays in the energy region 40–1000 GeV

A large stack of lead-emulsion sandwich detector assembly was flown over Hyderabad, India. High energy gamma rays at the float altitude were unambiguously identified from the cascades they induced, and their energies reliably determined by improved methods. From an analysis of 163 gamma rays of energy ≳ 30 GeV, it is found that the differential energy spectrum is represented by the power lawJ _r (E)= 129·4E ^{−2·62±0·12} photons m⁻² sr⁻¹sec⁻¹ GeV⁻¹ at an effective atmospheric depth of 14·3 g cm⁻²; this is the first reliable balloon measurement of atmospheric gamma rays in the energy range 40–1000 GeV. After correcting for the gamma rays radiated by the primary cosmic ray electrons, the production spectrum of gamma rays, resulting from the collisions of cosmic ray nuclei with air nuclei, at the top of the atmosphere isP _r (E, 0)=8·2 × 10⁻⁴ E^2.60±0.09 photons g⁻¹sr⁻¹sec⁻¹ GeV⁻¹. The atmospheric propagation of the electromagnetic component due to the cascade process is also derived from the gamma ray production spectrum.     

Probing pseudo-Dirac neutrino through detection of neutrino-induced muons from gamma ray burst neutrinos

The possibility to verify the pseudo-Dirac nature of neutrinos is investigated here via the detection of ultra-high energy neutrinos from distant cosmological objects like γ-ray bursts (GRBs). The very long baseline and the energy range from ∼TeV to ∼EeV for such neutrinos invoke the likelihood to probe very small pseudo-Dirac splittings. The expected secondary muons from such neutrinos that can be detected by a kilometer scale detector such as ICECUBE is calculated and compared with the same in the case of mass-flavour oscillations and for no oscillation cases. The calculated muon yields indicate that to probe such small pseudo-Dirac splittings one needs to look for a nearby GRB (red shift z ∼ 0.03 or less) whereas for a distant GRB (z ∼ 1) the flux will be much depleted and such phenomenon cannot be distinguished. Also calculated are the muon-to-shower ratios.      

Energetic neutrons and gamma rays measured on the Aryabhata satellite

An experiment to measure energetic neutrons and gamma rays in space was launched in the first Indian scientific satellite,Aryobhata, on April 19, 1975. From this experiment, the first measurements in space of the Earth’s albedo fiux of neutrons of energy between 20 and 500 MeV have been made; the values obtained for two mean geomagnetic vertical cut-off rigidities of 5.6 and 17.0 GV are (6.3±0.4)×10⁻² and (1.4±0.3)×10⁻² neutrons cm⁻² sec⁻¹ respectively. These measurements confirm that protons arising from cosmic ray albedo neutron decay, can adequately account for the protons in the inner radiation belt. Observations on gamma rays of energy between 0.2 and 24 MeV have enabled the determination of the total background gamma ray flux in space as a function of latitude. This in turn has permitted useful information on the diffuse cosmic gamma rays. We have also observed four events that showed sudden increases in the gamma ray counting rates between 0.2 and 4.0 MeV. Observational details of these events are given.     

Origin of cosmic rays

Cosmic rays were discovered in 1911 but it is only now that some ideas are beginning to emerge as to their origin. This paper will examine the present evidence concerning the origin question over the whole energy range, from 10⁹ eV to 10²⁰ eV. At the lowest energies, (10⁹–10¹⁰ eV), the new subject of gamma ray astronomy plays a crucial role and a galactic origin is favoured. At higher energies (10¹²–10¹⁷ eV) recent measurements of the anisotropies in arrival directions also suggest a galactic origin, although the evidence is not as strong. At the very highest energies it seems likely that some, at least, of the particles come from outside the galaxy although the non-existence of the cut-off at about 6 × 10¹⁹ eV arising from interactions with the cosmological relict radiation provides a paradox. The likely future areas of advance in this fascinating subject will be indicated. Based on the B. B. Roy memorial lectures delivered at Calcutta University, February 1–3, 1978.     

SVOM gamma ray monitor

The space-based multi-band astronomical Variable Object Monitor (SVOM) mission is dedicated to the detection, localization and broad-band study of gamma-ray bursts (GRBs) and other high-energy transient phenomena. The gamma ray monitor (GRM) onboard is designed to observe GRBs up to 5 MeV. With this instrument, one of the key GRB parameters, E _peak, can be easily measured in the hard X-ray band. It can achieve a detection rate of 100 GRBs per year which ensures the scientific output of SVOM.     

Ionization states of cosmic rays:Anuradha (IONS) experiment in Spacelab-3

The measurements of the ionization states, composition, energy spectra and spatial distribution of heavy ions of helium to iron of energies 10–100 MeV/amu in the anomalous cosmic rays are of major importance in understanding their origin which is unknown at present.Anuradha (IONS) cosmic ray experiment in Spacelab-3 was designed to determine the above properties in near earth space and this had a highly successful flight and operations aboard the shuttle Challenger at an orbital altitude of 352 km during 29 April to 6 May 1985. The instrument employs solid state nuclear track detectors (CR-39) of high sensitivity and large collecting area of about 800 cm² and determines the arrival time information of particles with active elements. Experimental methods, flight operations and preliminary results are briefly described. Initial results indicate that relatively high fluxes of low energy cosmic ray α-particles, oxygen group and heavier ions were obtained. The flight period corresponded to that of quiet Sun and the level of solar activity was close to solar minimum. It is estimated that about 10,000 events of low energy cosmic ray alpha particles with time annotation are recorded in the detector together with similar number of events of oxygen and heavier ions of low energy cosmic rays. The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion.     

Search for UHE cosmic sources with a large-area underground muon detector

Summary The newly discovered gamma-ray emission from Cyg-X 3 with energies up to 2·10¹⁶eV gives the first evidence that particle acceleration in galactic gamma-ray sources can reach energies of the order of 10⁴ TeV. We discuss the detectability of this type of sources by an underground muon tracking detector with area of the order of ∼1000 m² and the physical information which could be obtained in this way. Paper presented at the 2° Convegno Nazionale di Fisica Cosmica, held at L'Aquila, 29 May–2 June 1984.     

Observations of high-energy hadron-gamma families with extremely large lateral spreads

Summary Two very high-energy hadron-gamma families, named ?Halina? and ?C141G4836?, with unusually large lateral spread were detected by the carbon chamber of the Pamir emulsion chamber experiment. The total observed energies of the events are 3540 TeV and 2290 TeV, respectively (E ^(γ)≥2 TeV). The events have extraordinarily wide lateral spread both in electromagnetic component and hadronic component and they are rich in hadrons. One of the lateral characteristics of the events is described in the form of ER-flow density, Δ≡d(ΣER)/d(InR). Both of the experimental events have a very largeER-flow density of gamma-rays, Δ∼17 GeV·km forE _γ≥4 TeV and a high value ofER-flow density is arising from both high particle density and largeER of individual particles. It is shown that the longitudinal and lateral characteristics of the experimental data cannot be fully explained by model calculations even when we consider the contributions of heavy nuclei in primary particles if we assume no fundamental change in elementary process. To speed up publication, the authors of this paper has agreed to not receive the proofs for correction.     

Velocity variation of internal shock waves in gamma ray bursts: Observational properties

The work uses the data in the TTS mode of BATSE to analyze the time lags and pulse widths of GRB960113 and GRB960722 in high as well as low energy bands. The results show that their time lags increase monotonously. This phenomenon can reasonably be interpreted with the model of internal shock waves of γ-ray bursts (GRB). Perhaps we obtain the direct observational evidence for the fireball model of GRBs for the first time.     

Charm hadroproduction cross-section up to 100 TeV from measurements of the cosmic-ray muon angular distribution. Results of the Mont Blanc experiment

Summary Accurate calculations of the angular distributions of underground conventional and prompt muons have been performed. The dependence of the angular enhancement functions on the primary spectrum, cross-sections, inclusive distributions, K/π ratio and survival probability have been studied and found to be negligible. The results have been used to interpret the data from the Mont Blanc experiment in the depth range (4200ρ5800) hg/cm². Since the measurements extend over a limited angular range (<60°) the ratio between the flux of prompt to conventional muons of higher energy (>1 TeV) is obtained with large associated statistical errors. In order to obtain the charm production cross-section in the energy region (50ρ100) TeV, accurate measurements over a very large angular range (>70°) at depths higher than 5000 hg/cm² are required.

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Riassunto Sono state calcolate le distribuzioni angolari di muoni convenzionali e pronti sottoterra ed è stata studiata la loro dipendenza, risultata trascurabile, dalla forma dello spettro primario, sezione d'urto, distribuzioni inclusive, rapporto di produzione K/π e probabilità di sopravvivenza. Questi risultati sono stati usati per interpretare i dati ottenuti nell'esperimento del Monte Bianco nell'intervallo di profondità (4200ρ5800) hg/cm². Poiché le misure si estendono solo sino a 60° il rapporto tra muoni pronti e convenzionali di alta energia (>1 TeV) è ottenuto con grande errore statistico. Se ne conclude che per derivare la sezione d'urto di produzione di charm nell'intervallo di energia (50ρ100) TeV sono necessarie misure accurate ad alta profondità (>5000 hg/cm²) ed estese sino ad oltre 70°.

     

γ射线在LSO晶体中的能量沉积

采用蒙特卡罗程序MCNP计算了γ射线在LSO晶体中的能量沉积分布并与相应的实验结果进行了对比,验证了该方法的正确性。在此基础上计算了不同能量的γ射线在LSO晶体中的能量沉积分布,分析了γ射线与物质的不同作用对晶体中能量沉积分布的影响,总结出在晶体轴向和径向的能量沉积分布规律。轴向上,不同能量γ射线在LSO晶体中的能量沉积近似为指数分布,在表面能量沉积密度较小;在径向方向,γ射线在入射轴线上能量沉积密度很高,在距入射轴较近的区域,主要是次级电子产生沉积能量,随着距离的增大,γ射线能量沉积逐渐减小;在距入射轴较远的区域,能量沉积主要是散射γ射线产生。     

Ultrahigh-energy cosmic rays: Possible origin and spectrum

The complicated shape of the cosmic ray spectrum recorded by giant arrays in the energy range 10¹⁷–10²⁰ eV is analyzed. It is shown that in the energy region ∼10¹⁸–10¹⁹ eV the spectrum probably coincides with the injection spectrum whose exponent is equal approximately to 3.2–3.3. The flatter component in the energy region (3.2–5.0)×10¹⁹ eV is due to braking of extragalactic protons on primordial photons (the cosmic background radiation). At energies exceeding 3.2×10¹⁹ eV the spectrum does not have a blackbody cutoff. The possibility of determining the distances at which cosmic rays originate and investigating the evolution of their sources on the basis of ultrahigh-energy cosmic ray data is discussed. Zh. éksp. Teor. Fiz. 113, 12–20 (January 1998)     

High-energy neutrinos from gamma ray bursts

We treat high-energy neutrino production in gamma ray bursts (GRBs). Detailed calculations of photomeson neutrino production are presented for the collapsar model, where internal nonthermal synchrotron radiation is the primary target photon field, and the supranova model, where external pulsar-wind synchrotron radiation provides important additional target photons. Detection of greater, similar 10 TeV neutrinos from GRBs with Doppler factors > or approximately 200, inferred from gamma-ray observations, would support the supranova model. Detection of < or approximately 10 TeV neutrinos is possible for neutrinos formed from nuclear production. Only the most powerful bursts at fluence levels > or approximately 3 x 10(-4) erg cm(-2) offer a realistic prospect for detection of nu(mu).     

Cosmic rays from the knee to the highest energies

This review summarizes recent developments in the understanding of high-energy cosmic rays. It focuses on galactic and presumably extragalactic particles in the energy range from the knee (10¹⁵ eV ) up to the highest energies observed (>10²⁰ eV). Emphasis is put on observational results, their interpretation, and the global picture of cosmic rays that has emerged during the last decade.     

X-ray flares of γ-ray bursts: Quakes of solid quark stars?

A star-quake model is proposed to understand X-ray flares of both long and short γ-ray bursts (GRBs) in a solid quark star regime. Two kinds of central engines for GRBs are available if pulsar-like stars are actually (solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found that a quark star could be solidified about 10³ to 10⁶ s later after its birth if the critical temperature of phase transition is a few Metga-electron-volts, and then a new source of free energy (i.e., elastic and gravitational ones, rather than rotational or magnetic energy) could be possible to power GRB X-ray flares. Supported by the National Natural Science Foundation of China (Grant Nos. 10573002, 10778611, and 10873002), the National Basic Research Program of China (Grant No. 2009CB824800), the Research Foundation of Guangxi University (Grant No. M30520), and the LCWR (Grant No. LHXZ200602)     

Scission gamma rays

Gamma rays probably emitted by the fissioning nucleus ²³⁶U* at the instant of the break of the neck or within the time of about 10⁻²¹ s after or before this were discovered in the experiment devoted to searches for the effect of rotation of the fissioning nucleus in the process ²³⁵U($ \vec n $ \vec n , γf) and performed in a polarized beam of cold neutrons from the MEPHISTO Guideline at the FRM II Munich reactor. Detailed investigations revealed that the angular distribution of these gamma rays is compatible with the assumption of the dipole character of the radiation and that their energy spectrum differs substantially from the spectrum of prompt fission gamma rays. In the measured interval 250–600 keV, this spectrum can be described by an exponential function at the exponent value of α = −5 × 10⁻³ keV⁻¹. The mechanism of radiation of such gamma rays is not known at the present time. Theoretical models based on the phenomenon of the electric giant dipole resonance in a strongly deformed fissioning nucleus or in a fission fragment predict harder radiation whose spectrum differs substantially from the spectrum measured in the present study.     

Search for strong gravitational lensing effect in the current GRB data of BATSE

Because gamma-ray bursts(GRBs)trace the high-z universe,there is an appreciable probability for a GRB to be gravitational lensed by galaxies in the universe.Herein we consider the gravitational lensing effect of GRBs contributed by the dark matter halos in galaxies.Assuming that all halos have the singular isothermal sphere(SIS)mass profile in the mass range 1010h?1M?M2×1013h?1M?and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample,we calculated the gravitational lensing probability in BATSE,Swift/BAT and Fermi/GBM GRBs,respectively.With an derived probability result in BATSE GRBs,we searched for lensed GRB pairs in the BATSE5B GRB Spectral catalog.The search did not find any convincing gravitationally lensed events.We discuss our result and future observations for GRB lensing observation.