Detecting axionlike particles with gamma ray telescopes

We propose that axionlike particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to a detectable signature in the spectra of high-energy gamma-ray sources. This occurs as a result of gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the "Hillas criterion", such as jets of active galactic nuclei or hot spots of radio galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV range and by ground-based gamma-ray telescopes in the TeV range.     

A method of measurement of extragalactic magnetic fields by TeV gamma ray telescopes

A method is proposed for measuring extragalactic magnetic fields in observations of TeV γ rays from distant sources. Multi-TeV γ rays from these sources interact with the infrared photon background producing secondary electrons and positrons, which can be just slightly deflected by extragalactic magnetic fields before they emit secondary γ rays via inverse Compton scattering of cosmic microwave background photons. Secondary γ rays emitted toward an observer on the Earth can be detected as an extended emission around an initially point source. The energy dependent angular profile of the extended emission is related to the strength of the extragalactic magnetic field along the line of sight. Small magnetic fields B ≤ 10⁻¹² G in the voids of the large scale structure can be measured in this way. The text was submitted by the authors in English     

Double pair production by ultra-high-energy cosmic ray photons

Using the CompHEP package, we provide a detailed estimate of the influence of double e ⁺ e ⁻ pair production (DPP) by photons on the propagation of ultra-high-energy electromagnetic cascades. We show that in the models where the cosmic ray photon energy reaches a few 10³ EeV, a refined DPP analysis may lead to a substantial difference in the predicted photon spectrum compared to the previous rough estimates. The article is published in the original.     

Neutralino pair production in a $\gamma \gamma $ collider

We present a complete one-loop study of the process and the predicted cross section in a Linear Collider. A suitable numerical code, PLATONlc, valid for any set of real MSSM parameters, is released. This study and code are complementary to those suitable for dark matter detection through the inverse process describing neutralino-neutralino annihilation at rest, which were presented previously. If SUSY is realized in nature, both codes should be very helpful in future astrophysical and collider studies of the neutralino sector.Received: 6 November 2003, Published online: 9 January 2004Programme dActions Intégrées Franco-Hellenique, Platon 04100 UM.     

Central exclusive meson pair production in the perturbative regime at hadron colliders

The central exclusive production (CEP) of heavy resonance states that subsequently decay into meson pairs, \(M\overline{M}\), is an important signature for such processes at hadron colliders. However, there is a potentially important background from the direct QCD production of meson pairs, as mediated for example by the exclusive \(gg\to M\overline{M}\) hard scattering subprocess. This is in fact an interesting process in its own right, testing novel aspects of perturbative QCD technology. We explicitly calculate the \(gg \to M\overline{M}\) helicity amplitudes for different meson states within the hard exclusive formalism, and comment on the application of MHV techniques to the calculation. Using these results, we describe how meson pair CEP can be calculated in the perturbative regime, and present some sample numerical predictions for a variety of final states. We also briefly consider the dominant non-perturbative contributions, which are expected to be important when the meson transverse momentum is small.     

Tunable gamma ray generation

In this note, we wish to point out that utilizing presently available technology it is possible to construct an intense, modulated and polarized γ-ray source which can be used for spectroscopy purposes to good advantage.     

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.     

Short duration gamma ray bursts

After a short review of gamma ray bursts (GRBs), we discuss the physical implications of strong statistical correlations seen among some of the parameters of short duration bursts (T ₉₀ < 2 s). Finally, we conclude with a brief sketch of a new unified model for long and short GRBs.     

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.     

The AGNs and the extragalactic gamma ray background

The first part of this paper describes the identification of γ-ray AGNs. The database of cosmic γ-rays above 100 MeV from the SAS-2 satellite has been analysed to identify γ-ray emissions from 11 quasars, 3 BL Lac Objects and 1 radiogalaxy. Further investigations of the relationship between their γ-ray fluxes in different energy regions (>100 MeV and 35-100 MeV) and the relationship between their γ-ray fluxes and their redshifts, support that the sources detected are genuine extragalactic objects.The second part of this paper describes the determination of the contribution from AGNs to the extragalactic γ-ray background. The SAS-2 γ-ray data have been employed to determine the functional relationships between the absolute γ-ray luminosities L_γ and the absolute optical luminosities of quasars andSeyfert galaxies. From these, their contribution to the extragalaxtic γ-ray background can be derived. We have shown that quasars (B<20) and Seyfert (Type 1 and 1.5) galaxies together contribute to a substantial part (about 59%) of the diffuse γ-ray background in the 35-100 MeV range. Therefore we conclude that the extragalactic γ-ray background is likely to be generated by active galaxies such as quasars and Seyfert galaxies.     

Digital logarithmic airborne gamma ray spectrometer

A new digital logarithmic airborne gamma ray spectrometer is designed in this study. The spectrometer adopts a high-speed and high-accuracy logarithmic amplifier (LOG114) to amplify the pulse signal logarithmically and to improve the utilization of the ADC dynamic range because the low-energy pulse signal has a larger gain than the high-energy pulse signal. After energy calibration, the spectrometer can clearly distinguish photopeaks at 239, 352, 583 and 609 keV in the low-energy spectral sections. The photopeak energy resolution of ¹³⁷Cs improves to 6.75% from the original 7.8%. Furthermore, the energy resolution of three photopeaks, namely, K, U, and Th, is maintained, and the overall stability of the energy spectrum is increased through potassium peak spectrum stabilization. Thus, it is possible to effectively measure energy from 20 keV to 10 MeV.     

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).     

Searching for high-energy gamma emissions from cosmic gamma ray bursts

We present the results from our search for gamma ray bursts of high energy with the Andyrchy air shower array of the Baksan Neutrino Observatory of the Russian Academy of Sciences’ Institute for Nuclear Research using experimental data for the period 1996–2006 (live time, 2290 days). These data were recorded by the array in the mode of detecting single-particle components of cosmic rays.     

Internal pair production in alpha-decay

For the probability of the internal pair production in -decay a value of the order of 10^–12 has been obtained which is about 3 orders of magnitude below the experimental results. The internal pair production in -decay is supposed to be due to excited states in nuclei.Dedicated to Professor Ivan Úlehla on the occasion of his sixtieth birthday.