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.     

Determination of energies of cosmic-ray nuclei in the region above 1 TeV

A method is proposed for measuring energies of particles in the region above 1 TeV. The method is based on detecting the greatest specific energy deposition in hadronic cascades propagating in dense matter. This makes it possible to improve accuracy in measuring energy by thin calorimeters in studying the energy spectra of high-energy cosmic rays at high altitudes. Attainable accuracies in measuring energy are considered for protons and He nuclei. The results of a relevant simulation are compared with the results of a satellite-borne experiment with Kosmos-1713.     

Angular distribution and linear polarization of the gamma rays from oriented 56Co nuclei

Measurements are reported on the beta-gamma and gamma-gamma coincident radiation observed in the decay of ⁵⁶Co and on the angular distribution and linear polarization of the gamma rays emitted by oriented ⁵⁶Co nuclei. Discrepancies between various proposed decay schemes have been removed by means of coincidence measurements (performed at room temperature). Experiments with oriented nuclei (using low temperature techniques) gave information about the multipole order of the gamma rays, the mixing ratio of two multipoles and the electric or magnetic character of the transitions. As a result, evidence is presented for a decay scheme of ⁵⁶Co and for spin and parity assignments to the excited levels in ⁵⁶Fe (see fig. 10). A possible theoretical interpretation of some of these levels is discussed. A review is given of the data available from other experiments.     

Simulation of photodisintegration of heavy nuclei

A comparative study of the results of the simulations of the photodisintegration of heavy nuclei in the energy range corresponding to the giant dipole resonance by the TALYS software package and by a combined model of is carried out. The cross sections of photoabsorption, photoneutron, and photoproton reactions and of the excitation of isomeric states for Hg and ²⁰⁸Pb isotopes are calculated. The results of the calculations are compared with the known experimental data.     

Low energy theorem and photodisintegration of light nuclei

d(γ, n)p, ³H(γ, n)d, ³He(γ, p)d and ⁴He(γ, d)d reactions are studied using a low-energy theorem independently of any dynamical assumptions. This reproduces cross-section data at low energy for the first three reactions and gives a relativistic extension of the usual effective range approximation.     

Directional distribution of high-energy gamma rays from hot 125, 127Cs and 171Lu compound nuclei

Gamma-gamma directional correlations have been measured following ¹²C + ^113,115In and ¹⁵⁹Tb reactions at 100 MeV. Directional distribution coefficients have been determined for the gamma-ray spectrum between 2 and 16 MeV. For energies above 10 MeV the results for both reactions are in disagreement with interpretations in terms of the decay of the giant dipole resonance statistically excited either in a permanently deformed prolate compound nucleus undergoing collective rotation or an oblate nucleus with the angular momentum along the axis of symmetry. For the reaction on Tb indications of a quadrupole component at energies around 10 MeV are presented.     

Total cross-section measurements for the production of nuclear gamma rays from light nuclei by low-energy deuterons

The thick target yields of the reactions ⁶Li, ⁹Be, ¹⁰B(d, nγ) for specific final nucleus γ-rays have been measured between deuteron bombarding energies of 48 and 170 keV. The measured thick target yields are used, together with recently published values of the stopping power of low-energy deuterons in matter, to infer the total reaction cross sections for the production of the specific γ-rays between deuteron energies of 65 and 160 keV. The cross sections are compared to appropriate Coulomb barrier penetration probabilities and the astrophysical functions S(E) are deduced.     

The Carpet-3 experiment to search for diffuse gamma rays with energies of more than 100 TeV

An experiment for measuring the flux of cosmic diffuse gamma rays with energies above 100 TeV (the Carpet-3 air shower array) is now being prepared at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. The preparations entail a substantial increase of the areas of both the muon detector and the surface air shower array. The experiment’s sensitivity to showers generated by primary gamma rays is estimated for different configurations of the array. In addition, preliminary estimates of the upper limit on the flux of diffuse gamma rays with energies higher than 1.3 PeV, derived using experimental data from the old Carpet-2 array, are presented for a net exposure time of 9.2 years.     

Gamma ray and π0 production from hydrogen and complex nuclei by 270–375 MeV gamma rays

Measurements are reported on the differential cross section for secondary gamma ray production on hydrogen and nuclear targets at 90° in the laboratory through the interactions of primary gamma rays in the energy range 270–375 MeV. A difference method using bremsstrahlung beams at different end point energies was employed. The gamma ray detector was a high resolution Nal(Tl) spectrometer and time of flight discrimination was used to reject neutrons. For incident gamma rays in the range 270–375 MeV the first pion nucleon resonance is strongly excited and the observed gamma ray yields are consistent with those expected due to an admixture of coherent and incoherent π⁰ photoproduction in the resonance region. The experiment marks the first successful use of a large Nal(Tl) crystals as a gamma ray spectrometer at a high energy electron linear accelerator, despite the low duty cycle and its accompanying difficulties for such detectors.     

Thermal-neutron capture gamma rays from natural calcium

Gamma rays from thermal-neutron capture in natural Ca and enriched ⁴⁰Ca were investigated with a 5 cm³ Ge(Li) detector. Many low-energy γ-lines have been found. More than 90% of the γ-rays result from capture in ⁴⁰Ca and about 5% from capture in ⁴⁴Ca. From the data a decay scheme of ⁴¹Ca and a partial decay scheme of ⁴⁵Ca were constructed. The Q-values for the reactions ⁴⁰Ca(n, γ)⁴¹Ca and ⁴⁴Ca(n, γ)⁴⁵Ca were determined as Q = 8363.4±1.0 and 7418.1±3.0 keV,respectively.In ⁴¹Ca, it is found that hole states preferentially decay to hole states, and single-particle states to single-particle states.     

Proper motion of gamma rays from microhalo sources

I discuss the prospects of detecting the smallest dark matter bound structures present in the Milky Way by searching for the proper motion of gamma-ray sources in the upcoming Gamma Ray Large Area Space Telescope all sky map. I show that for dark matter particle candidates that couple to photons the detection of at least one gamma-ray microhalo source with proper motion places a constraint on the couplings and mass of the dark matter particle.     

Detection of high-energy gamma rays from winter thunderclouds

A report is made on a comprehensive observation of a burstlike gamma-ray emission from thunderclouds on the Sea of Japan, during strong thunderstorms on 6 January 2007. The detected emission, lasting for approximately 40 sec, preceded cloud-to-ground lightning discharges. The burst spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung photons originating from relativistic electrons. This ground-based observation provides the first clear evidence that strong electric fields in thunderclouds can continuously accelerate electrons beyond 10 MeV prior to lightning discharges.     

Direction of the anisotropy vector of TeV cosmic rays

The preliminary results of measuring the direction of the stellar anisotropy vector of cosmic rays with the Carpet array at the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) are presented. The direction of the anisotropy vector is determined by analyzing the distribution of time delays of the signal from distant detectors of the array with respect to its central part. It is shown that the anisotropy vector has the direction α₀ (R.A.) ≈ 1.5 h, δ₀ ≈ 62° in the equatorial coordinate system. At such a direction, the CR anisotropy measured with the Baksan Underground Scintillation Telescope and the Andyrchi array is ≈0.2%.