Search for extragalactic sources of ultrahigh-energy cosmic rays

Possible extragalactic sources of cosmic rays with energies above 4 × 10¹⁹ eV detected at the Yakutsk EAS array are sought. The correlation of the shower arrival directions with objects from Véron’s catalog that are located closer than 100 Mpc from the Earth confirms the observations at the Pierre Auger Observatory, as well as the Greisen-Zatsepin-Kuzmin effect on the spectrum of cosmic rays. The detailed analysis of the data reveals the classes of objects belonging to the active galactic nuclei that are the most probable sources of ultrahigh-energy cosmic rays.     

Energy spectrum of cosmic ray muons above 10 TeV according to BUST data

The energy spectrum of cosmic ray muons in the range of several TeV to PeV obtained through the analysis of multiple interactions of muons (the pair meter technique) in the Baksan Underground Scintillation Telescope (BUST) is presented. Results are compared with prior BUST data on the muon energy spectrum measurements and data of other experiments, along with calculations for different muon spectrum models.     

Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p⊥<2.0 GeV/c the yield andp⊥-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p??<2.0 GeV/c the yield andp??-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

Search for sources of primary cosmic radiation at energies above 10<Superscript>14</Superscript> eV

The results obtained at the separate installation of the Tien Shan station, intended for continuous studies, are analyzed with the aim of searching for local sources of primary cosmic radiation (PCR) at energies of 10¹⁴ − 10¹⁵ eV. Arrival directions in equatorial coordinates are determined for 35 millions of recorded extensive air showers (EAS) from PCR. The directions where the standard deviation of the number of events exceeds a certain value are separated. These can be the directions along which neutral primary cosmic particles (γ-rays and others) come from PCR sources. Some directions coincide with the results of other installations and pulsar positions.     

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.     

Search for 10TeV Gamma-Ray Bursts

A search for gamma-ray bursts at 1OTeV energy region was made using data of Yangbajing air shower experiment in Tibet.About 4×10⁸ events were analysed to search for shower clusters appearing in a given time interval and a given small sky bin. An equal-zenith angle method is adopted to estimate the background. Some clusters show excesses over the background but with less significance as the evidence of gamma-ray bursts.The much higher sensitivity of the Yangbajing second phase array to the detection of 1OTeV gamma-ray bursts is discussed.     

TeV signatures of compact UHECR accelerators

We numerically study particle acceleration by the electric field induced near the horizon of a rotating supermassive (M ～ 10⁹–10¹⁰M_⊙) black hole embedded in the magnetic field B. We find that acceleration of protons to the energy E ～ 10²⁰ eV is possible only at extreme values of M and B. We also find that the acceleration is very inefficient and is accompanied by a broad-band MeV-TeV radiation whose total power exceeds the total power emitted in ultrahigh energy cosmic rays (UHECRs) at least by a factor of 1000. This implies that if O(10) nearby quasar remnants were sources of proton events with an energy E > 10²⁰ eV, then each quasar remnant would, e.g., overshine the Crab Nebula by more than two orders of magnitude in the TeV energy band. Recent TeV observations exclude this possibility. A model in which O(100) sources are situated at 100–1000 Mpc is not ruled out and can be experimentally tested by present TeV γ-ray telescopes. Such a model can explain the observed UHECR flux at moderate energies E ≈ (4–5) × 10¹⁹ eV.     

Lorentz violation for photons and ultrahigh-energy cosmic rays

Lorentz symmetry breaking at very high energies may lead to photon dispersion relations of the form omega2=k2+xink2(k/MPl)n with new terms suppressed by a power n of the Planck mass MPl. We show that first and second order terms of size |xi1|>orsimilar10(-14) and xi2相似文献   

Search for direct photons from S-Au collisions at 200 GeV/nucleon by the CERES Collaboration

In this note we comment on a recent publication in this journal by the CERES (NA45) Collaboration [1]. The authors report to have determined an upper limit on the direct photon yield relative to the decay photon yield in S + Au collisions of 14% and 7% by two different methods, respectively. We argue that these limits are unsupported by the results and analysis of the CERES data. The systematic error estimates quoted in the CERES analysis are consistently overly optimistic. Using more realistic estimates of the various error contributions and propagating them appropriately we arrive at a direct photon upper limit which at best is 20% of the inclusive photon yield, and most probably is much higher.     

Search for sources of cosmic rays in the region of the knee: Part II

This paper reports on new results obtained from analyzing the arrival directions of extensive air showers detected at the Prototip ShAL-1000 array in the period from the end of August 1997 to February 2001. The results are examined using the method proposed by Alexandreas and colleagues, which has been widely employed for analyzing the data obtained from other experiments. The existence of the previously revealed zones with an excessive flux of cosmic rays at energies in the range of the knee and the closeness of the coordinates of these zones to those of the possible astrophysical cosmic-ray sources are confirmed.     

Search for antihelium in cosmic rays

The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 in a 51.7° orbit at altitudes between 320 and 390 km. A total of 2.86×10⁶ helium nuclei were observed in the rigidity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to helium of <1.1×10⁻⁶ is obtained.     

Absorption of TeV photons andκ-deformed poincaré algebra

We consider the process of collision between a hard photon and a soft photon producing an electron-positron pair, under the assumption that the kinematics be described according to theκ-deformation of theD=4 Poincaré algebra. We emphasize the relevance of this analysis for the understanding of the puzzling observations of multi-TeV photons from Markarian 501. We find a significant effect of theκ-deformation for processes above threshold, while, in agreement with a previous study, we find that there is no leading-order deformation of the threshold condition Presented at the 10th International Colloquium on Quantum Groups: “Quantum Groups and Integrable Systems”, Prague, 21–23 June 2001.     

Search for anisotropy of ultrahigh-energy cosmic rays

It is shown that a statistically significant anisotropy exists in the arrival directions of cosmic rays with energies ∼1×10¹⁷ eV and 4×10¹⁸ eV. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 289–292 (10 September 1997)     

Search for 100 TeV gamma-rays from SN 1987 A

Summary We present the results of a search for very high energy γ-rays (E _γ≈100 TeV) from SN 1987A between August 1987 and May 1988. No counting rate excess from the source is observed. The larger enhancement is seen in January 1988, but is statistically not significant (1.4 s.d.). The derived upper limits to the γ-ray and proton luminosities of the SN areL _γ≤1.9·10⁴⁰ erg/s andL _p≤1.2·10⁴² erg/s. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.