Yakutsk Experiments Research Articles

SN 1987A as a possible source of cosmic rays up to energy 1018 eV by Yakutsk EAS array data

Yakutsk extensive air shower array experiment is the only one which is in operation since 1974, it has the best exposure around 1018eV. It is believed that the balk of cosmic rays up to ~1017eV originated in supernova remnants [1]. Under certain conditions they can accelerate cosmic rays up to ~1018eV or even higher [2]. However, there is a lack of an undoubted observational evidence for such idea. Here we show that Yakutsk experiment probably has observed cosmic rays from SN 1987A. We found that before 1996 the intensity of cosmic rays in energy range 1017–1018eV fluctuate near some average value, then it start to increase. The increase of intensity total 45±5%. It is also accompanied by significant changes in cosmic ray composition; it became heavier – iron dominated. In the last 3-4 years it is a trend to return to the initial state. This peculiarities can be explained by the appearance of SN 1987A. If so, then our results demonstrate that supernova remnants can indeed accelerate cosmic rays up to ~1018e V. This is an important step in understanding the cosmic ray origin problem and reveal the great importance of long-term and multicomponent observations of ultra-high energy cosmic rays.

Space-time structure of signals in scintillation detectors of extensive air showers

The space-time evolution of a signal in scintillation detectors used at the Yakutsk array is calculated within the quark-gluon string model. It follows from the calculations of the temporal distributions of the signal that the time to sample all particles at the distances 100, 600, 1000, and 1500 m is 0.1, 1, 2.5, and 4 μs respectively. At large distances from the shower axis in the region of superhigh energies, about 60–70% of the signal is sampled within the sampling time of 2 μs adopted in the experiment. At the distance 600 m from the shower axis, the estimated sampling time of all particles agrees with the one adopted in the Yakutsk experiment.

Recent results from the Yakutsk experiment: The development of EAS and the energy spectrum and primary particle mass composition in the energy region of 10 15–10 19 eV

Experimental data obtained at the Yakutsk array after the modernization in 1993 are analyzed. The characteristics of EAS longitudinal and radial development found from the charged particle flux and EAS Cerenkov light registered at the Yakutsk array complex are presented. The energy spectrum of EAS obtained from Cerenkov light and an estimate of the mass composition of primary cosmic rays are presented.

Magnetic deflections and possible sources of clustered ultra-high-energy cosmic rays

Corrections for the deflection of charged cosmic-ray particles by the regular component of the Galactic magnetic field (GMF) destroy the ultra-high-energy cosmic-ray clusters observed by the AGASA and Yakutsk experiments, as well as the cluster of five cosmic rays observed by the AGASA, HiRes and Yakutsk experiments, for any of conventional GMF models. This may mean that either the clusters are accidental, or the clustered cosmic rays have neutral primaries, or the GMF models do not work. Assuming the latter possibility, we study the fiveplet in more detail and find which deflections would not destroy the cluster and possibly make it tighter. For different primary charges, we discuss possible astrophysical sources of the particles forming the fiveplet.

On the Cross-Correlation between the Arrival Direction of Ultra-High-Energy Cosmic Rays, BL Lacertae Objects, and EGRET Detections: A New Way to Identify EGRET Sources?

With the aim of testing recent claims for a particularly strong correlation between ultra-high-energy cosmic rays (UHECRs), observed with the AGASA and Yakutsk experiments, and a sample of BL Lacertae objects, we conduct a blind statistical assessment. We search for associations between the same set of BL Lac objects and the arrival directions of 33 relevant UHECRs observed with the Haverah Park and Volcano Ranch experiments. Within the accuracy of the angle determination, there are no positional coincidences. The probability that this null result arises as a statistical fluctuation from the strongly correlated case is less than 5%. This implies that the possible correlation between the arrival directions of UHECRs and BL Lac objects is not statistically sustained. We discuss the impact of our findings on the proposed additional connection among UHECRs, BL Lac objects, and EGRET γ-ray blazars. Recently, such an association was used as a classification technique for EGRET sources. Here we show that its main underlying hypothesis (i.e., the EGRET angular uncertainty is twice that quoted in the third EGRET catalog) grossly underestimates the goodness of existing γ-ray data.

Has the GZK suppression been discovered?

The energy spectra of ultra-high energy cosmic rays reported by the AGASA, Fly's Eye, Haverah Park, HiRes, and Yakutsk experiments are all shown to be in agreement with each other for energies below 1020 eV (after small adjustments, within the known uncertainties, of the absolute energy scales). The data from HiRes, Fly's Eye, and Yakutsk are consistent with the expected flux suppression above 5×1019 eV due to interactions of cosmic rays with the cosmic microwave background, the Greisen–Zatsepin–Kuzmin (GZK) suppression, and are inconsistent with a smooth extrapolation of the observed cosmic-ray energy spectrum to energies >5×1019 eV. AGASA data show an excess of events above 1020 eV, compared to the predicted GZK suppression and to the flux measured by the other experiments.

BL Lacs are probable sources of UHECR

We identify the subset of cosmic rays observed by AGASA and Yakutsk experiments which exhibits the largest degree of autocorrelations. We search for astrophysical sources which can be responsible for these autocorrelations and find significant correlations with BL Lacs at small angles (∼ 2°) with probability of statistical fluctuation to be 3 × 10 −4, including all penalties.

Correlation function of ultrahigh-energy cosmic rays favors point sources

We calculate the angular two-point correlation function of ultrahigh-energy cosmic rays (UHECR) observed in the AGASA and Yakutsk experiments. In both data sets, there is a strong signal at the highest energies, which is concentrated in the first bin of size equal to the angular resolution of the experiment. For the uniform distribution of sources, the probability of chance clustering is 4×10−6. Correlations are absent or insignificant at larger angles. This favors the models with compact sources of UHECR

Depth of maximum of extensive air showers and cosmic ray composition above eV in the geometrical multichain model of nuclei interactions

The depth of maximum for extensive air showers measured by Fly's Eye and Yakutsk experiments is analysed. The analysis depends on the hadronic interaction model that determines cascade development. The novel feature found in the cascading process for nucleus-nucleus collisions at high energies leads to a fast increase of the inelasticity in heavy nuclei interactions without changing the hadron-hadron interaction properties. This effects the development of the extensive air showers initiated by heavy primaries. The detailed calculations were performed using the recently developed geometrical multichain model and the CORSIKA simulation code. The agreement with data on average depth of shower maxima, the falling slope of the maxima distribution, and these distribution widths are found for the very heavy cosmic ray mass spectrum (slightly heavier than expected in the diffusion model at about and similar to the Fly's Eye composition at this energy).

On estimating the energy of giant air-shower primaries

The principal methods used currently to evaluate the energy of giant air-shower primaries are compared in the light of a conflict between a recent report from the Yakutsk experiment Diminstein et al. (1982) and results of experiments at Haverah Park Cunningham et al. (1980) and Volcano Ranch Linsley (1973), Watson (1975). It is shown that the different methods used for converting from a ground parameter to primary energy in these three experiments give excellent agreement. The cosmic-ray energy spectrum is redetermined, with improved statistical accuracy, for the highest energies, above 4*1019 eV.