Search

The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) was launched in 2017 April from Wanaka, New Zealand. The plan of this mission of opportunity on a NASA super pressure balloon test flight was to circle the southern hemisphere. The primary scientific goal was to make the first observations of ultra-high-energy cosmic-ray extensive air showers (EASs) by looking down on the atmosphere with an ultraviolet (UV) fluorescence telescope from suborbital altitude (33~km). After 12~days and 4~hours aloft, the flight was terminated prematurely in the Pacific Ocean. Before the flight, the instrument was tested extensively in the West Desert of Utah, USA, with UV point sources and lasers. The test results indicated that the instrument had sensitivity to EASs of approximately 3 EeV. Simulations of the telescope system, telescope on time, and realized flight trajectory predicted an observation of about 1 event assuming clear sky conditions. The effects of high clouds were estimated to reduce this value by approximately a factor of 2. A manual search and a machine-learning-based search did not find any EAS signals in these data. Here we review the EUSO-SPB1 instrument and flight and the EAS search., Comment: 18 pages, 19 figures

This is a collection of papers presented by the JEM-EUSO Collaboration at the 38th International Cosmic Ray Conference (Nagoya, Japan, July 26-August 3, 2023)

JEM--EUSO is an international program for the development of space-based Ultra-High Energy Cosmic Ray observatories. The program consists of a series of missions which are either under development or in the data analysis phase. All instruments are based on a wide-field-of-view telescope, which operates in the near-UV range, designed to detect the fluorescence light emitted by extensive air showers in the atmosphere. We describe the simulation software ESAFin the framework of the JEM--EUSO program and explain the physical assumptions used. We present here the implementation of the JEM--EUSO, POEMMA, K--EUSO, TUS, Mini--EUSO, EUSO--SPB1 and EUSO--TA configurations in ESAF. For the first time ESAF simulation outputs are compared with experimental data.

The trigger logic of the Tracking Ultraviolet Setup (TUS) and Multiwavelength Imaging New Instrument for the Extreme Universe Space Observatory (Mini-EUSO) space-based projects of the Joint Experiment Missions - EUSO (JEM-EUSO) program is summarized. The performance results on the search for ultra-high energy cosmic rays are presented.

The present white paper is submitted as part of the "Snowmass" process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy physics. It summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades., Comment: Prepared as a solicited white paper for the 2021 Snowmass process. To be published in the Journal of High Energy Astrophysics. v2: fixed typos in author list. v3: included all community feedback received by July 1st 2022 and added the list of endorsers. v4 is the post-reviewer preprint accepted to Astroparticle Physics vol. 149

K-EUSO (KLYPVE-EUSO) is a planned orbital mission aimed at studying ultra-high energy cosmic rays (UHECRs) by detecting fluorescence and Cherenkov light emitted by extensive air showers in the nocturnal atmosphere of Earth in the ultraviolet (UV) range. The observatory is being developed within the JEM-EUSO collaboration and is planned to be deployed on the International Space Station after 2025 and operated for at least two years. The telescope, consisting of $\sim10^{5}$ independent pixels, will allow a spatial resolution of $\sim0.6$ km on the ground, and, from a 400 km altitude, it will achieve a large and full sky exposure to sample the highest energy range of the UHECR spectrum. We provide a comprehensive review of the current status of the development of the K-EUSO experiment, paying special attention to its hardware parts and expected performance. We demonstrate how results of the K-EUSO mission can complement the achievements of the existing ground-based experiments and push forward the intriguing studies of ultra-high energy cosmic rays, as well as bring new knowledge about other phenomena manifesting themselves in the atmosphere in the UV range., Comment: 26 pages

Compilation of papers presented by the JEM-EUSO Collaboration at the 37th International Cosmic Ray Conference (ICRC), held on July 12-23, 2021 (online) in Berlin, Germany., Comment: html page with links to the JEM-EUSO Collaboration papers presented at ICRC-2021, Berlin, Germany

TUS (Tracking Ultraviolet Set-up) was the world's first orbital detector aimed at testing the principle of observing ultra-high energy cosmic rays (UHECRs) with a space-based fluorescence telescope. TUS was launched into orbit on 28th April 2016 as a part of the scientific payload of the Lomonosov satellite, and its mission continued for 1.5 years. During this time, its exposure reached $\sim1550$ km$^2$ sr yr for primary energy $\gtrsim400$ EeV, and a number of extensive air showers-like events were registered. The shape and kinematics of the signal in these events closely resembled those expected from UHECRs but amplitudes of the signal and some other features were in contradiction with this assumption. A detailed analysis of one of EAS-like events (TUS161003) revealed that a primary cosmic ray would need to have an energy $\gtrsim1$ ZeV in order to produce a light curve of the observed amplitude, which is incompatible with the cosmic ray spectrum obtained with ground-based experiments. More than this, the slant depth of the shower maximum be the signal produced by a cosmic particle, was estimated as $\lesssim500$ g/cm$^2$, which corresponds to cosmic rays around 1 PeV. We present a preliminary discussion of a hypothesis that the TUS161003 event and perhaps some other bright EAS-like events could be produced by relativistic dust grains, which were considered a possible component of the cosmic ray flux beyond the GZK cut-off some time ago., Comment: Proceedings of the 37th International Cosmic Ray Conference (ICRC 2021), Berlin, Germany

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to accurately observe ultra-high-energy cosmic rays (UHECRs) and cosmic neutrinos from space with sensitivity over the full celestial sky. POEMMA will observe the extensive air showers (EASs) from UHECRs and UHE neutrinos above 20 EeV via air fluorescence. Additionally, POEMMA will observe the Cherenkov signal from upward-moving EASs induced by Earth-interacting tau neutrinos above 20 PeV. The POEMMA spacecraft are designed to quickly re-orientate to follow up transient neutrino sources and obtain unparalleled neutrino flux sensitivity. Developed as a NASA Astrophysics Probe-class mission, POEMMA consists of two identical satellites flying in loose formation in 525 km altitude orbits. Each POEMMA instrument incorporates a wide field-of-view (45$^\circ$) Schmidt telescope with over 6 m$^2$ of collecting area. The hybrid focal surface of each telescope includes a fast (1~$\mu$s) near-ultraviolet camera for EAS fluorescence observations and an ultrafast (10~ns) optical camera for Cherenkov EAS observations. In a 5-year mission, POEMMA will provide measurements that open new multi-messenger windows onto the most energetic events in the universe, enabling the study of new astrophysics and particle physics at these otherwise inaccessible energies., Comment: 66 pages, 53 figures; JCAP accepted version

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to identify the sources of Ultra-High-Energy Cosmic Rays (UHECRs) and to observe cosmic neutrinos, both with full-sky coverage. Developed as a NASA Astrophysics Probe-class mission, POEMMA consists of two spacecraft flying in a loose formation at 525 km altitude, 28.5 deg inclination orbits. Each spacecraft hosts a Schmidt telescope with a large collecting area and wide field of view. A novel focal plane is optimized to observe both the UV fluorescence signal from extensive air showers (EASs) and the beamed optical Cherenkov signals from EASs. In POEMMA-stereo fluorescence mode, POEMMA will measure the spectrum, composition, and full-sky distribution of the UHECRs above 20 EeV with high statistics along with remarkable sensitivity to UHE neutrinos. The spacecraft are designed to quickly re-orient to a POEMMA-limb mode to observe neutrino emission from Target-of-Opportunity (ToO) transient astrophysical sources viewed just below the Earth's limb. In this mode, POEMMA will have unique sensitivity to cosmic neutrino tau events above 20 PeV by measuring the upward-moving EASs induced by the decay of the emerging tau leptons following the interactions of neutrino tau inside the Earth., Comment: 3 pages, no figures, LoI for Snowmass 2021

Compilation of papers presented by the JEM-EUSO Collaboration at the 36th International Cosmic Ray Conference (ICRC), held July 24 through August 1, 2019 in Madison, Wisconsin., Comment: links to the 24 papers published in arXiv

TUS (Tracking Ultraviolet Set-up) is the world's first orbital detector of ultra-high-energy cosmic rays (UHECRs). It was launched into orbit on 28th April 2016 as a part of the scientific payload of the Lomonosov satellite. The main aim of the mission was to test the technique of measuring the ultraviolet fluorescence and Cherenkov radiation of extensive air showers generated by primary cosmic rays with energies above ~100 EeV in the Earth atmosphere from space. During its operation for 1.5 years, TUS registered almost 80,000 events with a few of them satisfying conditions anticipated for extensive air showers (EASs) initiated by UHECRs. Here we discuss an event registered on 3rd October 2016. The event was measured in perfect observation conditions as an ultraviolet track in the nocturnal atmosphere of the Earth, with the kinematics and the light curve similar to those expected from an EAS. A reconstruction of parameters of a primary particle gave the zenith angle around 44$^\circ$ but an extreme energy not compatible with the cosmic ray energy spectrum obtained with ground-based experiments. We discuss in details all conditions of registering the event, explain the reconstruction procedure and its limitations and comment on possible sources of the signal, both of anthropogenic and astrophysical origin. We believe this detection represents a significant milestone in the space-based observation of UHECRs because it proves the capability of an orbital telescope to detect light signals with the apparent motion and light shape similar to what are expected from EASs. This is important for the on-going development of the future missions KLYPVE-EUSO and POEMMA, aimed for studying UHECRs from space., Comment: 24 pages; v2: important changes to address comments by the anonymous referee; main conclusions unchanged

TUS (Tracking Ultraviolet Set-up), the first orbital telescope of ultra-high energy cosmic rays (UHECRs), has demonstrated that instruments of this kind have much broader capabilities and can also detect meteors, transient luminous events, anthropogenic glow and other processes taking place in Earth atmosphere in the UV frequency range. In this short letter, we address the question if an orbital UHECR detector can also register gamma-ray bursts (GRBs) via the fluorescent glow of irradiated nocturnal atmosphere. An analysis of the Fermi GBM catalog of GRBs and properties of several active and perspective instruments reveals that a detector with parameters of the optical system similar to those of the KLYPVE-EUSO (K-EUSO) or POEMMA telescopes and an appropriate \slow-mode" trigger will be able to observe only two GRBs in average every year of operation. POEMMA will register up to 3-4 GRBs in a year of operation in the stereo mode., Comment: 12 pages

KLYPVE-EUSO (K-EUSO) is a planned orbital detector of ultra-high-energy cosmic rays (UHECRs), which is to be deployed on board the International Space Station. K-EUSO is expected to have a uniform exposure over the celestial sphere and register from 120 to 500 UHECRs at energies above 57 EeV in a 2-year mission. We employed the TransportCR and CRPropa 3 packages to estimate prospects of detecting a large-scale anisotropy of ultra-high-energy cosmic rays from a nearby source with K-EUSO. Nearby active galactic nuclei Centaurus A, M82, NGC 253, M87 and Fornax A were considered as possible sources of UHECRs. A minimal model for extragalactic cosmic rays and neutrinos by Kachelriess, Kalashev, Ostapchenko and Semikoz (2017) was chosen for definiteness. We demonstrate that an observation of $\gtrsim300$ events will allow detecting a large-scale anisotropy with a high confidence level providing the fraction of from-source events is $\simeq$10-15%, depending on a particular source. The threshold fraction decreases with an increasing sample size. We also discuss if an overdensity originating from a nearby source can be observed at around the ankle in case a similar anisotropy is found beyond 57 EeV. The results are generic and hold for other future experiments with a uniform exposure of the celestial sphere., Comment: 18 pages; version 2: discussion extended, references added, results unchanged; version 3: numerous changes to address comments of the referee; accepted by JCAP

EUSO-Balloon is a pathfinder mission for the Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO). It was launched on the moonless night of the 25$^{th}$ of August 2014 from Timmins, Canada. The flight ended successfully after maintaining the target altitude of 38 km for five hours. One part of the mission was a 2.5 hour underflight using a helicopter equipped with three UV light sources (LED, xenon flasher and laser) to perform an inflight calibration and examine the detectors capability to measure tracks moving at the speed of light. We describe the helicopter laser system and details of the underflight as well as how the laser tracks were recorded and found in the data. These are the first recorded laser tracks measured from a fluorescence detector looking down on the atmosphere. Finally, we present a first reconstruction of the direction of the laser tracks relative to the detector., Comment: 18 pages, 14 figures

TUS (Track Ultraviolet Setup) is the first space experiment aimed to check the possibility of registering extreme energy cosmic rays (EECRs) at E>50 EeV by measuring the fluorescence signal of extensive air showers in the atmosphere. The detector operates as a part of the scientific payload of the Lomonosov satellite for more than a year. We describe an algorithm of searching for EECR events in the TUS data and briefly discuss a number of candidates selected by formal criteria., Comment: 13 pages

The origin and nature of extreme energy cosmic rays (EECRs), which have energies above the 50 EeV, the Greisen-Zatsepin-Kuzmin (GZK) energy limit, is one of the most interesting and complicated problems in modern cosmic-ray physics. Existing ground-based detectors have helped to obtain remarkable results in studying cosmic rays before and after the GZK limit, but have also produced some contradictions in our understanding of cosmic ray mass composition. Moreover, each of these detectors covers only a part of the celestial sphere, which poses problems for studying the arrival directions of EECRs and identifying their sources. As a new generation of EECR space detectors, TUS (Tracking Ultraviolet Set-up), KLYPVE and JEM-EUSO, are intended to study the most energetic cosmic-ray particles, providing larger, uniform exposures of the entire celestial sphere. The TUS detector, launched on board the Lomonosov satellite on April 28, 2016, from Vostochny Cosmodrome in Russia, is the first of these. It employs a single-mirror optical system and a photomultiplier tube matrix as a photo-detector and will test the fluorescent method of measuring EECRs from space. Utilizing the Earth's atmosphere as a huge calorimeter, it is expected to detect EECRs with energies above 100 EeV. It will also be able to register slower atmospheric transient events: atmospheric fluorescence in electrical discharges of various types including precipitating electrons escaping the magnetosphere and from the radiation of meteors passing through the atmosphere. We describe the design of the TUS detector and present results of different ground-based tests and simulations., Comment: 19 pages; v2: figures 6 and 9 replaced to match the published version

TUS (Tracking Ultraviolet Set-up), the first orbital detector of extreme energy cosmic rays (EECRs), those with energies above 50 EeV, was launched into orbit on April 28, 2016, as a part of the Lomonosov satellite scientific payload. The main aim of the mission is to test a technique of registering fluorescent and Cherenkov radiation of extensive air showers generated by EECRs in the atmosphere with a space telescope. We present preliminary results of its operation in a mode dedicated to registering extensive air showers in the period from August 16, 2016, to November 4, 2016. No EECRs have been conclusively identified in the data yet, but the diversity of ultraviolet emission in the atmosphere was found to be unexpectedly rich. We discuss typical examples of data obtained with TUS and their possible origin. The data is important for obtaining more accurate estimates of the nocturnal ultraviolet glow of the atmosphere, necessary for successful development of more advanced orbital EECR detectors including those of the KLYPVE (K-EUSO) and JEM-EUSO missions., Comment: 18 pages; v2: references fixed; v3: minor changes to address referee's comments

On April 28, 2016, the Lomonosov satellite, equipped with a number of scientific instruments, was launched into orbit. Here we present briefly some of the results obtained with the first orbital telescope of extreme energy cosmic rays TUS and by a group of detectors aimed at multi-messenger observations of gamma-ray bursts., Comment: XXV ECRS 2016 Proceedings - eConf C16-09-04.3

In the present-day cosmic ray data, the strongest indication of anisotropy of the ultrahigh energy cosmic rays is the 20-degree hotspot observed by the Telescope Array with the statistical significance of 3.4\sigma. In this work, we study the possibility of detecting such a spot by space-based all-sky observatories. We show that if the detected luminosity of the hotspot is attributed to a physical effect and not a statistical fluctuation, the KLYPVE and JEM-EUSO experiments would need to collect ~300 events with E>57 EeV in order to detect the hotspot at the 5\sigma\ confidence level with the 68% probability. We also study the dependence of the detection prospects on the hotspot luminosity., Comment: 4 pages; v2: minor style changes to match the published version

Two types of orbital detectors of extreme energy cosmic rays are being developed nowadays: (i) TUS and KLYPVE with reflecting optical systems (mirrors) and (ii) JEM-EUSO with high-transmittance Fresnel lenses. They will cover much larger areas than existing ground-based arrays and almost uniformly monitor the celestial sphere. The TUS detector is the pioneering mission developed in SINP MSU in cooperation with several Russian and foreign institutions. It has relatively small field of view (+/-4.5 deg), which corresponds to a ground area of 6.4x10^3 sq.km. The telescope consists of a Fresnel-type mirror-concentrator (~2 sq.m) and a photo receiver (a matrix of 16x16 photomultiplier tubes). It is to be deployed on the Lomonosov satellite, and is currently at the final stage of preflight tests. Recently, SINP MSU began the KLYPVE project to be installed on board of the Russian segment of the ISS. The optical system of this detector contains a larger primary mirror (10 sq.m), which allows decreasing the energy threshold. The total effective field of view will be at least +/-14 degrees to exceed the annual exposure of the existing ground-based experiments. Several configurations of the detector are being currently considered. Finally, JEM-EUSO is a wide field of view (+/-30 deg) detector. The optics is composed of two curved double-sided Fresnel lenses with 2.65 m external diameter, a precision diffractive middle lens and a pupil. The ultraviolet photons are focused onto the focal surface, which consists of nearly 5000 multi-anode photomultipliers. It is developed by a large international collaboration. All three orbital detectors have multi-purpose character due to continuous monitoring of various atmospheric phenomena. The present status of development of the TUS and KLYPVE missions is reported, and a brief comparison of the projects with JEM-EUSO is given., Comment: 18 pages; based on the rapporteur talk given by M.I. Panasyuk at ECRS-2014; v2: a few minor language issues fixed thanks to the editor; to be published in the proceedings

Results of a blind search for localized regions of an excessive flux of cosmic rays in the energy range from 50 TeV to 20 PeV with the data of the FIAN KLARA-Chronotron experiment, the EAS MSU array and the Prototype of the EAS-1000 array are presented. A number of regions with a significant excess of the registered flux over an expected isotropic background are found. Some of the regions are present in at least two of the data sets considered., Comment: 5 pages, 2 figures; to be published in the proceedings of the 33rd Russian Cosmic Ray Conference (Dubna, 11-15 August, 2014)

We study anisotropy of cosmic rays in the energy range 0.2-1.4 EeV at intermediate angular scales using the public data set of the Pierre Auger Observatory. At certain scales, the analysis reveals a number of deviations from the isotropic distribution with the statistical significance above three standard deviations. It also demonstrates that the anisotropy evolves with energy. If confirmed with the complete Auger or Telescope Array data sets, the result can shed new light on the structure of galactic magnetic fields and the problem of transition from galactic to extragalactic cosmic rays., Comment: 9 pages, 2 figures

A search for anisotropy at different scales in the arrival directions of cosmic rays with energies above 1 PeV is performed with data of the Tunka-133 array. A number of regions with angular sizes up to approximately 30 degrees that deviate from the uniform background with a statistical significance greater than three standard deviations are found using the shuffling technique both in the complete data set and its subsets in different energy ranges. Some regions with an excess of cosmic rays correlate with the distribution of possible cosmic ray sources. A comparison of the results with a similar analysis of the legacy data of the EAS MSU array is presented., Comment: The paper has been withdrawn by the author due to a possible overestimation of the statistical significance of the results

The origin of ultra-high-energy cosmic rays (UHECRs) is one of the most intriguing problems of modern cosmic ray physics. We briefly review the main astrophysical models of their origin and the forthcoming orbital experiments TUS and JEM-EUSO, and discuss how the new data can help one solve the long-standing puzzle., Comment: 4 pages; prepared for ECRS-2012 (http://ecrs2012.sinp.msu.ru/); v2: a reference added

Recent results of Milagro, Tibet, ARGO-YBJ and IceCube experiments on the small-scale anisotropy of Galactic cosmic rays (CRs) with energies from units up to a few hundred TeV arise a question on a possible nature of the observed phenomenon, as well as on the anisotropy of CRs at higher energies. An analysis of a small-scale anisotropy of CRs with energies at around PeV registered with the EAS MSU array presented in the article, reveals a number of regions with an excessive flux. A typical size of the regions varies from 3 up to 12 degrees. We study correlation of these regions with positions of potential astrophysical sources of CRs and discuss a possible origin of the observed anisotropy., Comment: 16 pages with 4 figures

Three regions of excessive flux of cosmic rays with energies of the order of PeV are found in the experimental data of the EAS MSU array at a confidence level greater than 4\sigma. For two of them, there are similar regions in the experimental data of the EAS-1000 Prototype array. One of the interesting features of the regions is the absence of supernova remnants in their vicinities, traditionally considered as the main sources of Galactic cosmic rays, but the presence of isolated pulsars, some of which are able to accelerate heavy nuclei up to energies close to PeV. In our opinion, this favors the assumption that isolated pulsars are able to contribute to the flux of Galactic cosmic rays more than is usually assumed., Comment: 7 pages. The preprint fixes errors that appeared in the English version of the article published in Bull. Rus. Acad. Sci. Physics, 2011, Vol.75, p.342. Original Russian text: Izv. RAN., Ser. Fiz., 2011, Vol.75, p.371. V2: a few typos fixed, layout improved. arXiv admin note: repeats content from arXiv:0907.3192

Angular distributions of extensive air showers with different number of charged particles in the range 2.5x10^5--4x10^7 are derived using the experimental data obtained with the EAS MSU array. Possible approximations of the obtained distributions with different empiric functions available in literature, are analysed. It is shown that the exponential function provides the best approximation of the angular distributions in the sense of the chi-squared criterion., Comment: 5 pages including 1 figure

An analysis of arrival directions of extensive air showers (EAS) registered with the EAS MSU and EAS-1000 prototype arrays has revealed a region of excessive flux of PeV cosmic rays in the direction toward pulsars PSR J1840+5640 and LAT PSR J1836+5925 at significance level up to 4.5sigma. The first of the pulsars was discovered almost 30 years ago and is a well-studied old radio pulsar located at the distance of 1.7pc from the Solar system. The second pulsar belongs to a new type of pulsars, discovered by the space gamma-ray observatory Fermi, pulsations of which are not observed in optical and radio wavelengths but only in the gamma-ray range of energies (gamma-ray-only pulsars). In our opinion, the existence of the region of excessive flux of cosmic rays registered with two different arrays provides a strong evidence that isolated pulsars can give a noticeable contribution to the flux of Galactic cosmic rays in the PeV energy range., Comment: 14 pages; v.2: a few remarks to match a version accepted for Astronomy Letters added. They can be found by redefining the \NEW command in the preamble of the LaTeX file

An analysis of arrival directions of extensive air showers generated by cosmic rays in the PeV energy range and registered with the EAS MSU and EAS-1000 Prototype arrays reveals a considerable number of regions of excessive flux of cosmic rays. We present results of comparative analysis of regions found in the two data sets, estimate probabilities of their appearance, and discuss correlation of their locations with coordinates of possible astrophysical sources of PeV cosmic rays., Comment: 4 pages, 3 figures; presented at the 30th Russian Cosmic Ray Conference, Saint-Petersburg, July 2-7, 2008

New results of an analysis of arrival directions of extensive air showers registered with the EAS--1000 Prototype array from August 1997 till February 1999 are presented. The method of Alexandreas et al., which has been used for analysis of data registered with CYGNUS, Milagrito, HEGRA AIROBICC, KASCADE and a number of other experiments, is employed. The existence of zones of excessive flux of cosmic rays with energies in the region of the knee is confirmed, as well as closeness of the zones to coordinates of possible astrophysical cosmic ray sources., Comment: 4 pp; Proc. of the 29th Russian Conf. on Cosmic Rays (Moscow, August'06)

We study arrival directions of 1.4x10^6 extensive air showers (EAS) registered with the EAS--1000 Prototype Array in the energy range 0.1--10 PeV. By applying an iterative algorithm that provides uniform distribution of the data with respect to sidereal time and azimuthal angles, we find a number of zones with excessive flux of cosmic rays (CRs) at >=3 sigma level. We compare locations of the zones with positions of galactic supernova remnants (SNRs), pulsars, open star clusters, and regions of ionized hydrogen and find remarkable coincidences, which may witness in favour of the hypothesis that certain objects of these types, including the SNRs Cassiopeia A, the Crab Nebula, the Monogem Ring and some other, provide a noticeable contribution to the flux of CRs in the PeV range of energies. In addition, we find certain signs of a contribution from the M33 galaxy and a number of comparatively nearby groups of active galactic nuclei and interacting galaxies, in particular those in the Virgo cluster of galaxies. The results also provide some hints for a search of possible sources of ultra-high energy (UHE) cosmic rays and support an earlier idea that a part of both UHE and PeV CRs may originate from the same astrophysical objects., Comment: v.2: references added, conclusions (hopefully) clarified. Results unchanged

Bursts of the count rate of extensive air showers (EAS) lead to the appearance of clusters in time series that represent EAS arrival times. We apply methods of nonlinear time series analysis to twenty EAS cluster events found in the data set obtained with the EAS-1000 prototype array. In particular, we use the Grassberger-Procaccia algorithm to compute the correlation dimension of the time series in the vicinity of the clusters. We find that four cluster events produce signs of chaos in the corresponding time series. By applying a number of supplementary methods we assess that the nature of the observed behaviour of the correlation dimension is likely to be deterministic. We suggest a simple qualitative model that might explain an origin of clusters in general and "possibly chaotic" clusters in particular. Finally, we compare our conclusions with the results of similar investigations performed by the EAS-TOP and LAAS groups., Comment: An extended version of the paper to be submitted to Astroparticle Physics. Version 2: 22 pages, discussion extended, the main part shortened, accepted for publication. Version 1 is still valid (up to a number of typos)

We apply certain methods of nonlinear time series analysis to the extensive air shower clusters found earlier in the data set obtained with the EAS-1000 Prototype array. In particular, we use the Grassberger-Procaccia algorithm to compute the correlation dimension of samples in the vicinity of the clusters. The validity of the results is checked by surrogate data tests and some additional quantities. We compare our conclusions with the results of similar investigations performed by the EAS-TOP and LAAS groups., Comment: 4 pages; submitted to Izv. Ros. Akad. Nauk, Ser. Fiz

We perform cluster analysis of arrival times of extensive air showers (EAS) registered with the EAS-1000 Prototype array in the period from August, 1997 till February, 1999. We present twenty cluster events each consisting of one or several EAS clusters, study the dynamics of their development, and analyze the angular distribution of EAS in clusters. We find that there may be certain correlation between EAS clusters with mean electron number $\sim10^5$ on the one hand and gamma-ray bursts and ultrahigh energy cosmic rays on the other., Comment: 39 pages; v.2: on page 3, a typo in a formula for delay adjustment is fixed; v.3: the last paragraph of Sec.3 edited