On the Origin of Cosmic Rays

Part I. Cosmic Rays: 1. Galactic cosmic rays and galactic halo X-ray emission 2. Highly luminous radiogalaxies as sources of cosmic rays 3. Where is the cosmic-ray modulation boundary of the heliosphere? 4. Origin of primary cosmic rays above 1 TeV 5. Astrophysical discoveries derived from transient cosmic ray and solar flare particle earth-based investigations: the early years Part II. X-Ray, Gamma-Ray and Neutrino Astronomy: 6. How X-ray astronomy has extended the horizon of physics 7. Selected topics in high energy gamma-ray astrophysics 8. Cosmic gamma rays, the origin of cosmic rays, and the structure of the galaxy: the IRAS connection: reminiscences 9. Ultra-high-energy gamma-ray astronomy 10. Recent gamma-ray burst studies by Ginga 11. High-energy astrophysics in solar flares 12. High-energy gamma radiation from supernova 13. IMB detection of neutrinos from SN1987A: history and results 14. High-energy neutrino astronomy: project DUMAND Part III. Cosmology: 15. The cosmic quark-hadron phase transition 16. Ponderable soliton stars from early universe 17. Dark matter and the generation of cosmological structure Part IV. Reminiscences and Poetic Black Holes: 18. Contributions of Maurice M. Shapiro and his group to cosmic-ray astrophysics 19. From Jerusalem to heavenly realms - memoir of a cosmic journey 20. Maury Shapiro and ERICE 21. Black holes.

Accelerated particles are ubiquitous in the Cosmos and play a fundamental role in many processes governing the evolution of the Universe at all scales, from the sub-AU scale relevant for the formation and evolution of stars and planets to the Mpc scale involved in Galaxy assembly. We reveal the presence of energetic particles in many classes of astrophysical sources thanks to their production of non-thermal radiation, and we detect them directly at the Earth as cosmic rays. In the last two decades both direct and indirect observations have provided us a wealth of new, high-quality data about cosmic rays and their interactions both in sources and during propagation, in the Galaxy and in the Solar System. Some of the new data have confirmed existing theories about particle acceleration and propagation and their interplay with the environment in which they occur. Some others have brought about interesting surprises, whose interpretation is not straightforward within the standard framework and may require a change of paradigm in terms of our ideas about the origin of cosmic rays of different species or in different energy ranges. In this article, we focus on cosmic rays of galactic origin, namely with energies below a few petaelectronvolts, where a steepening is observed in the spectrum of energetic particles detected at the Earth. We review the recent observational findings and the current status of the theory about the origin and propagation of galactic cosmic rays.

The probable connection between cosmic rays and the electromagnetic state of the interplanetary medium was recognized by Hannes Alfven as early as 1949 (Alfven, 1949, 1950); he pointed out that the properties of cosmic rays necessitate a mechanism, external to Earth but within the solar system, capable of accelerating particles to extremely high energies. In advocating the view of local origin for part of the cosmic-ray spectrum, Alfven and his colleagues developed a very general type of acceleration mechanism called ‘magnetic pumping’. The unique data set of the two Voyagers extends over an entire decade (1977–1987) and is most suitable to explore the problem of acceleration of charged particles in the heliosphere. The energy coverage of the Low Energy Charged Particle (LECP) experiment covers the range ~ 30 keV to several hundred MeV for ions and ~ 22 keV to several MeV for electrons. Selected observations of interplanetary acceleration events from ~ 1 to ~ 25 AU are presented and reviewed. These show frequent acceleration of ions to several tens of MeV in association with shocks; highest energies (≳220 MeV oxygen) were measured in the near-perpendicular (θ Bn ≃87.5°) shock of January 5, 1978 at ~1.9 AU, where electron acceleration was also observed. Examples of ion acceleration in association with corotating interaction regions are presented and discussed. It is shown that shock structures have profound effects on high-energy (≥ 70 MeV) cosmic rays, especially during solar minimum, when a negative latitudinal gradient was observed after early 1985 at all energies from ~ 70 MeV down to ~ 30 keV. By early 1987, most shock acceleration activity in the outer heliosphere (~ 25 to 30 AU) had ceased both in the ecliptic (Voyager-2) and at higher (~30°) ecliptic latitudes (Voyager-1). The totality of observations demonstrate that local acceleration to a few hundred MeV, and as high as a few GeV is continually present throughout the heliosphere. It should be noted that in 1954 when Alfven suggested local acceleration and containment of cosmic rays within the solar system, no one treated his suggestion seriously, at any energy. The observations reviewed in this paper illustrate once more Alfven’s remarkable prescience and demonstrate how unwise it is to dismiss his ideas.

We propose that cosmic rays interact mostly near their sources of origin. To be specic, we dierentiate the various supernovae by their mass of the progenitor star along the zero age main sequence. Stars between about 8 and 15 solar masses explode into the interstellar medium, and accelerate cosmic rays, as discussed by many for some time. From about 15 to 25 solar masses stars explode into their own stellar wind; this wind has built up a thin shell of both wind material and interstellar medium material in the red and blue giant phases preceding the supernova event. The shock accelerating cosmic ray particles races through that wind, gets loaded up with energetic particles, interacts while it goes, and nally smashes into the shell. While the shock goes out, it snowplows the entire wind into the pre-existing shell to form a composite shell. We propose that for the mass range 15 to 25 solar masses this composite shell is immediately broken up so that the time scale for interaction is caused by the breakup and so is convective. We note that the wind material for this range of zero age masses is a approximately half helium, and half hydrogen. The interactions in the composite wind-shell and the immediate environment produce positrons, gamma emission, but only few secondary nuclei, because for this mass range the enrichment in heavier elements is still minor. The energy spectrum of the gamma emission and the positrons produced corresponds then to the source spectrum. In contrast, from about 25 solar masses and up the wind is strongly enriched in heavy elements, and the wind shell is massive, comprising most of the initial zero age star's mass, as well as a good part of the local interstellar medium. We propose that for the interaction of the cosmic ray particles carried out by the shock in the snow-plow through the wind to the shell the interaction is diusive, and calculate the diusion coecient. This leads to a leakage time energy dependence of E 5=9 in the relativistic limit. This then gives an energy dependence of secondary nuclei, that matches the observations. There is a second component of positrons, and also gamma emission, but then at moderate energies all with the steeper energy dependence; spatial and velocity constraints give both a lower as well as an upper rigidity limit to the diusion approximation. One important element in such a picture is the steady mixing of newly enriched material throughout the star before the explosion, induced by Voigt-Eddington circulation caused by rotation. The mixed material is then ejected through the wind, which at the end provides the source material for cosmic ray injection. This means that by the time the nuclei are subject to acceleration, they should have decayed already to nal states, an eect which may be measureable in cosmic ray isotope ratios. Therefore, considering the history of the travel of cosmic rays through the normal interstellar medium, we can readily explain the ratio of secondaries to primaries, and at the same time use a spectrum of turbulence in the interstellar medium, a Kolmogorov spectrum, which is consistent with all other observational evidence. The escape time from the Galaxy is then proportional to E 1=3 in the relativistic range of particle energies. Translating this result into the language common in the literature, this means that interaction path as measured in gm/cm 2 and escape time can not be used synonymously.

Introduction to Large High Altitude Air Shower Observatory (LHAASO)

view Abstract Citations (12) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Origin of Cosmic Rays. III. Particle Acceleration by Global Spiral Shocks Duric, Nebojsa Abstract Cosmic-ray acceleration by global spiral shocks in galactic disks is investigated using existing theory. The diffusive shock acceleration (DSA) mechanism is discussed in the low-velocity regime represented by density wave shocks. It is found that a medium of T ≍ 104 K, partially to fully ionized, supports the DSA mechanism. It is concluded that existing theory permits particle acceleration by global, slow moving shocks as suggested by observational work on the spiral galaxy NGC 3310. Publication: The Astrophysical Journal Pub Date: May 1986 DOI: 10.1086/164148 Bibcode: 1986ApJ...304..111D Keywords: COSMIC RAYS: GENERAL; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3310; PARTICLE ACCELERATION; RADIO SOURCES: GALAXIES; SHOCK WAVES full text sources ADS | data products SIMBAD (1) NED (1) Related Materials (2) Part 1: 1986ApJ...304...82D Part 2: 1986ApJ...304...96D

In this paper we present a new five particle species hybrid model for calculating cosmic ray particle transport and acceleration in a dynamic heliospheric environment. In particular the effects of solar cycle related changes in the solar wind speed on the heliospheric geometry, solar wind flow and cosmic ray distribution are discussed, when a polar- ecliptic asymmetry at the inner boundary is modeled. It is shown that the disappearance of the fast solar wind over the solar poles toward solar maximum influences the geometry of the termination shock which is an important structure for cosmic ray acceleration. For solar maximum conditions, the shock radius is smaller in the polar regions and in the he- liospheric tail compared to solar minimum. These changes influence cosmic ray transport and acceleration in these re- gions, especially for the polarity cycle where positive parti- cles drift in along the heliospheric current sheet. For this po- larity cycle, and for both the anomalous and galactic cosmic ray protons, an increase in particle intensities at the shock in the heliospheric tail is computed as the shock moves in- ward toward the Sun. For the heliospheric nose, it is also shown that both the plasma speed and cosmic ray intensities are relative insensitive to changes in the latitudinal profile of the solar wind speed. Therefore toward solar maximum conditions there is a decrease in the nose-tail asymmetry of the computed cosmic ray distribution compared to solar min- imum conditions. shock fronts, the inner, the termination shock of the solar wind, and the outer, the bowshock of the interstellar ionized matter. The interstellar wind is a consequence of the rela- tive motion between the solar system and the local interstel- lar medium, while the inner solar wind results from the solar coronal outflow with asymptotically supersonic velocities. In the interface region between the two shocks a contact discon- tinuity forms, the heliopause, which separates both media by a surface which cannot penetrated by the plasmas.

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Galactic magnetic fields and cosmic rays are tightly bound up together. The fact that the energy density of cosmic rays in the local region of the Galaxy is approximately the same order of magnitude as the energy density of the magnetic field has led many authors to postulate that this is a universal phenomenon, i.e., that there is equipartition. Gamma ray observations of the Magellanic Clouds lead us to doubt the presence of such equipartition there, however. Doubt is raised, therefore, about the application of equipartition, and a fixed electron to proton ratio, by radio astronomers to observations of synchrotron radiation from galaxies in general.A consequence of the lack of equipartition may be that in some galaxies the cosmic ray intensity is increasing (or decreasing). The positive link between the strength of galactic magnetic fields and the star formation rate implies that dynamo action may not be the only source of galactic magnetic fields.

Using data from the Voyager and Pioneer spacecraft at distances up to 60 AU from the Sun to help define the effects of solar modulation, we have made a new estimate of the local interstellar cosmic-ray spectra and the associated energy density and ionization rate. The energy density, including the low-energy electron contribution, is ~1.80 eV cm-3, equivalent energetically to that in a 7 μG magnetic field. The ionization rate from this same cosmic-ray population, including a significant contribution from low-energy electrons, is (3-4) × 10-17 s-1 (H atom). This is most likely a minimum value and is not too different from estimates of the typical ionization rate required to heat the interstellar medium and maintain the diffuse ionized gas range from (3-30) × 10-17 s-1 (H atom) as a function of locale in the Galaxy. This suggests that cosmic rays could be a significant contributor to interstellar heating. The cosmic-ray ionization rate will be more or less uniform throughout the Galactic disk and also perpendicular to the disk according to the scale height of cosmic rays which may be ~1 kpc, thus providing a source of ionization at high Z values. The recent observation of low-energy particle acceleration at the heliospheric termination shock, which produces local ionization rates comparable to those due to Galactic cosmic rays, raises the interesting possibility that "hot spots," where the ionization rate due to locally accelerated particles may exceed 10-16 s-1 (H atom), may occur near massive stars with more powerful stellar winds.

Recent measurements of cosmic gamma ray intensities up to TeV energies have been used to estimate the spectral shape of the parent cosmic ray particles present in the interstellar medium. The case is made for the particle spectrum in the Inner Galaxy being flatter than locally and in the Outer Galaxy. Of various possible explanations we make the case for the propagation of the particles being different in the more turbulent interstellar medium of the Inner Galaxy. The characteristic parameter α for the so called anomalous diffusion is expected to be less in the Inner Galaxy than locally by about 0.2 and the corresponding power law spectral exponent of the cosmic ray particles differs from that locally by about Δγ 0.1.

The work is done within the framework of the PAMELA project [1]. The PAMELA is a space experiment for study of charged particles in the cosmic radiation that has been performed since the launch June 15 2006. This work is dedicated to the high energy cosmic ray proton and helium flux determination (an energy region from 50 GeV/nucleon) based on using a sampling electromagnetic calorimeter. The energy estimation was built on a measurement of a total deposited energy in the calorimeter and an applying of certain event selection criteria connected with an electromagnetic component of a hadronic shower. The helium-proton separation was performed by scintillation detectors of the PAMELA Time of Flight system. This method is indispensable to widen a measurable energy range and to receive additional information in the PAMELA experiment. The obtained energy spectra of protons and helium are presented. 1. Primary Cosmic-ray Helium and Proton Spectra Helium nuclei and Protons are the most abundant elements in cosmic rays. The primary cosmic-ray proton and helium spectrum knowledge is very important to understand the fundamental phenomena of cosmic ray physics. They include cosmic rays acceleration mechanisms, particle propagation, cosmic ray origin and the matter distribution in interstellar space. In addition the proton and helium fluxes contain an essential part of information to be known for a neutrinos absolute flux calculation for example in the movement a neutrino oscillations analysis. The energy range between 1TeV up to 10 TeV remains the most scantily explored one for cosmic ray protons and helium till now. There have been very few measurements for the high energy protons and helium spectra in previous time in balloon borne or satellite experiments, beginning from the PROTON satellites [2] till CREAM [3], but some questions have kept so yet.

I review here some of the current research on the propagation and the origin of galactic cosmic rays. The abundances of secondary nuclei, generated by spallation reactions in the interstellar medium, are well accounted for by simple models where cosmic rays escape from the galaxy and/or from their source in an energy dependent way; this may be due to the scattering of cosmic rays by resonant irregularities resulting from the general interstellar turbulence. Protons and helium nuclei in cosmic rays may have a different history than the rest of the particles. Supernovae are the most probable accelerators of cosmic rays. The shock acceleration mechanism can account for the energy budget of cosmic rays, and for their spectrum, but only up to a maximum energy <104–105 GeV for protons. Acceleration in an accretion shock surrounding a collapsed star may lead to higher energies. The source composition of cosmic rays is quite similar to that of ordinary matter, except that cosmic rays are comparatively poor in H and He by an order of magnitude. The abundances of the other elements mimick those of solar cosmic rays and of the solar corona, perhaps indicating that cosmic rays are injected by stellar flares. Other interpretations of the cosmic ray source abundance are discussed.

We present semi-analytical models of galactic outflows in high redshift galaxies driven by both hot thermal gas and non-thermal cosmic rays. Thermal pressure alone may not sustain a large scale outflow in low mass galaxies (i.e $M\sim 10^8$~M$_\odot$), in the presence of supernovae (SNe) feedback with large mass loading. We show that inclusion of cosmic ray pressure allows outflow solutions even in these galaxies. In massive galaxies for the same energy efficiency, cosmic ray driven winds can propagate to larger distances compared to pure thermally driven winds. On an average gas in the cosmic ray driven winds has a lower temperature which could aid detecting it through absorption lines in the spectra of background sources. Using our constrained semi-analytical models of galaxy formation (that explains the observed UV luminosity functions of galaxies) we study the influence of cosmic ray driven winds on the properties of the intergalactic medium (IGM) at different redshifts. In particular, we study the volume filling factor, average metallicity, cosmic ray and magnetic field energy densities for models invoking atomic cooled and molecular cooled halos. We show that the cosmic rays in the IGM could have enough energy that can be transferred to the thermal gas in presence of magnetic fields to influence the thermal history of the intergalactic medium. The significant volume filling and resulting strength of IGM magnetic fields can also account for recent $\gamma$-ray observations of blazars.

The physics of magnetic fields (B) and cosmic rays (CRs) have recently been included in simulations of galaxy formation. However, significant uncertainties remain in how these components affect galaxy evolution. To understand their common observational tracers, we analyse the magnetic fields in a set of high-resolution, magnetohydrodynamic, cosmological simulations of Milky-Way-like galaxies from the FIRE-2 project. We compare mock observables of magnetic field tracers for simulations with and without CRs to observations of Zeeman splitting and rotation/dispersion measures. We find reasonable agreement between simulations and observations in both the neutral and the ionized interstellar medium (ISM). We find that the simulated galaxies with CRs show weaker ISM |B| fields on average compared to their magnetic-field-only counterparts. This is a manifestation of the effects of CRs in the diffuse, low density inner circumgalactic medium (CGM). We find that equipartition between magnetic and cosmic ray energy densities may be valid at large (&amp;gt; 1 kpc) scales for typical ISM densities of Milky-Way-like galaxies, but not in their haloes. Within the ISM, the magnetic fields in our simulated galaxies follow a power-law scaling with gas density. The scaling extends down to neutral hydrogen number densities &amp;lt; 300 cm−3, in contrast to observationally derived models, but consistent with the observational measurements. Finally, we generate synthetic rotation measure (RM) profiles for projections of the simulated galaxies and compare to observational constraints in the CGM. While consistent with upper limits, improved data are needed to detect the predicted CGM RMs at 10–200 kpc and better constrain theoretical predictions.