Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants. All components of the cosmic rays show an ...intensity that decreases as a power law with increasing energy (for example as E-2.7). Electrons in particular lose energy rapidly through synchrotron and inverse Compton processes, resulting in a relatively short lifetime (about 105 years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away). Here we report an excess of galactic cosmic-ray electrons at energies of ∼300-800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar or micro-quasar) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza-Klein particle with a mass of about 620 GeV).
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Measurement of polarized light provides a direct probe of magnetic fields in collimated outflows (jets) of relativistic plasma from accreting stellar-mass black holes at cosmological distances. These ...outflows power brief and intense flashes of prompt gamma-rays known as Gamma Ray Bursts (GRBs), followed by longer-lived afterglow radiation detected across the electromagnetic spectrum. Rapid-response polarimetric observations of newly discovered GRBs have probed the initial afterglow phase. Linear polarization degrees as high as Π∼30% are detected minutes after the end of the prompt GRB emission, consistent with a stable, globally ordered magnetic field permeating the jet at large distances from the central source. In contrast, optical and gamma-ray observations during the prompt phase led to discordant and often controversial results, and no definitive conclusions on the origin of the prompt radiation or the configuration of the magnetic field could be derived. Here we report the detection of linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt gamma-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the GRB jet, closer to the central source, and show that the prompt GRB phase is produced via fast cooling synchrotron radiation in a large-scale magnetic field advected from the central black hole and distorted from dissipation processes within the jet.
Abstract
Experimental evidence in favor of or against the existence of a universal mechanism for the acceleration of charged particles in the Universe is analyzed from the modern standpoint. We adopt ...a purely phenomenological approach to this very intricate problem, discussing spatial scales that range from the magnetospheres of Earth and other planets of the Solar System to the Sun’s atmosphere, the heliosphere, supernovae, and extragalactic objects responsible for the generation of ultra-high-energy cosmic rays. We demonstrate a great variety of acceleration mechanisms operating in the Universe. However, data on the nuclear composition of accelerated particles obtained in numerous experiments may be indicative of a global nature of the Fermi-type stochastic acceleration mechanism inherent in various astrophysical objects. This mechanism may well be dominant over others, but a number of experimental observations are nevertheless inconsistent with that idea. It is possible that a hierarchy of accelerating mechanisms operates in some space objects, with preliminary acceleration by one mechanism followed by other mechanisms, acting sequentially or alternatively. We therefore discuss all currently available data for and against the global ‘presence’ of a Fermi-type acceleration mechanism.
The galactic cosmic ray (GCR) particle flux model has been developed by using the experimental data obtained during the solar cycles 21–24. The model calculates fluxes of GCR particles (with charge z ...from 1 to 28 and energy E from 80 up to 105 MeV/nucleon) in the interplanetary space (ecliptic plane) as a function of solar activity (sunspot number) and the heliocentric distance. GCR proton fluxes computed by the model for the case of a possible decrease in solar activity during solar cycles 25 and 26 are discussed.
Key Points
The GCR particle flux model is developed by using a wide range of experimental data obtained during the 21–24 solar cycles
GCR proton fluxes in interplanetary space depending on calendar time are calculated and discussed for 25th and 26th predicted solar cycles
This forecast indicates a continuing trend of solar activity reduction starting since the 23rd solar cycle
In 1966, Greisen and independently Zatsepin and Kuzmin published evidence for the existence of a relic (GZK) cutoff in the proton energy spectrum in ultra-high energy cosmic rays (UHECRs) above 5 × ...1019 eV. Half a century of experimental ground-based UHECR research has resulted in a large amount of data on energy spectra, anisotropy, and mass composition. The first space experiment to measure UHECRs was launched in 2016. In this paper, we discuss the results and prospects of experimental UHECR research in light of the proposed theoretical model of the GZK cutoff.
The origin and nature of extreme energy cosmic rays (EECRs), which have energies above the
5
⋅
10
19
eV
—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
10
20
eV
.
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.
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 44ˆ 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.
•Ni-Fe coatings with various structure were obtained via controlled electrodeposition.•A nonlinear change in hardness was found during the study by nanoindentation.•The explanation was found in the ...nature of elastoplastic energy relaxation.•Strong correlation between microstructure and deformation mechanisms was found.•The possibilities of the surface and volume hardening of material was shown.
This article contains the study of correlation between the microstructure, mechanical properties and mechanisms of elastoplastic deformation of Ni-Fe coatings that were grown in five electrodeposition modes and had fundamentally different microstructures. A nonlinear change in hardness was detected using nanoindentation. Explanation of the abnormal change in hardness was found in the nature of the relaxation method of elastoplastic energy under load. It is shown that the deformation of coatings with a grain size of 100 nm or more occurs due to dislocation slip. A decrease in grain size leads to the predominance of deformation due to rotations and sliding of grains, as well as surface and grain boundary diffusion. The effect of deformation mechanisms on the nanoscale hardness of Ni-Fe coatings was established. Full hardening of the coatings (both in the bulk and on the surface) was achieved while maintaining the balance of three mechanisms of elastoplastic deformation in the sample. Unique coatings consisting of two fractions of grains (70% of nano-grains and 30% of their agglomerates) demonstrate high crack resistance and full-depth hardening up to H = 7.4 GPa due to the release of deformation energy for amorphization and agglomeration of nanograins.
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Usually a thunderstorm region with lightning activity is necessary for the formation of known types of upper atmospheric transient luminous events (TLEs: sprites, emission of light and very low ...frequency perturbation, blue jets, etc.) with well-recognizable visible emissions. However, some "far-from-thunderstorm" transient events have been detected in some experiments. Measurements of transient atmospheric events (TAEs) were made on board the Vernov satellite by the sensitive UV and IR detector. Remote observation from the satellite's orbit provided measurements all over the globe and allowed us to study events associated with thunderstorms (lightning, TLEs) and unusual UV flashes (UV TAEs) far from thunderstorm regions. More than 8500 UV TAEs were measured by the Vernov satellite over the globe. Forty seven far-from-thunderstorm TAEs were selected having no lightning discharges during 1 h in a radius of 1000 km around the location of the event according to the Worldwide Lightning Location Network (WWLLN) and Vaisala Global Lightning Data Set (GLD360) data. Special attention was given to six events with complicated temporal structure and low luminosity in the IR channel. Their properties and atmospheric conditions were studied in detail. The analysis of cloud cover in addition to the lightning location networks data demonstrated the low probability of any lightning in the region of measurements.
The EAS Cherenkov light array Tunka-133, with ~ 3 km2 geometric area, is taking data since 2009.The array permits a detailed study of energy spectrum and mass composition of cosmic rays in the ...energy range from 6 · 1015 to 1018 eV. We describe the methods of time and amplitude calibration of the array and the methods of EAS parameters reconstruction. We present the all-particle energy spectrum, based on 7 seasons of operation.
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