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Cosmic Rays (cosmic + ray)

Distribution by Scientific Domains
Physics and Astronomy100%

Kinds of Cosmic Rays

  • energy cosmic ray
    		•

    Selected Abstracts

    Cosmic rays caught in the act

    ASTRONOMY & GEOPHYSICS, Issue 4 2009
    Article first published online: 20 JUL 200
    No abstract is available for this article. [source]

    A kinetic approach to cosmic-ray-induced streaming instability at supernova shocks

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009
    E. Amato
    ABSTRACT We show that a purely kinetic approach to the excitation of waves by cosmic rays in the vicinity of a shock front leads to predict the appearance of a non-Alfvénic fast-growing mode which has the same dispersion relation as that previously found by Bell in 2004 by treating the plasma in the magnetohydrodynamic approximation. The kinetic approach allows us to investigate the dependence of the dispersion relation of these waves on the microphysics of the current which compensates the cosmic ray flow. We also show that a resonant and a non-resonant mode may appear at the same time and one of the two may become dominant on the other depending on the conditions in the acceleration region. We discuss the role of the unstable modes for magnetic field amplification and particle acceleration in supernova remnants at different stages of the remnant evolution. [source]

    Hard X-ray emission of the Earth's atmosphere: Monte Carlo simulations

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
    S. Sazonov
    ABSTRACT We perform Monte Carlo simulations of cosmic ray-induced hard X-ray radiation from the Earth's atmosphere. We find that the shape of the spectrum emergent from the atmosphere in the energy range 25,300 keV is mainly determined by Compton scatterings and photoabsorption, and is almost insensitive to the incident cosmic ray spectrum. We provide a fitting formula for the hard X-ray surface brightness of the atmosphere as would be measured by a satellite-borne instrument, as a function of energy, solar modulation level, geomagnetic cut-off rigidity and zenith angle. A recent measurement by the INTEGRAL observatory of the atmospheric hard X-ray flux during the occultation of the cosmic X-ray background by the Earth agrees with our prediction within 10 per cent. This suggests that Earth observations could be used for in-orbit calibration of future hard X-ray telescopes. We also demonstrate that the hard X-ray spectra generated by cosmic rays in the crusts of the Moon, Mars and Mercury should be significantly different from that emitted by the Earth's atmosphere. [source]

    Coherent synchrotron emission from cosmic ray air showers

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
    Qinghuan Luo
    ABSTRACT Coherent synchrotron emission by particles moving along semi-infinite tracks is discussed, with a specific application to radio emission from air showers induced by high-energy cosmic rays. It is shown that in general, radiation from a particle moving along a semi-infinite orbit consists of usual synchrotron emission and modified impulsive bremsstrahlung. The latter component is due to the instantaneous onset of the curved trajectory of the emitting particle at its creation. Inclusion of the bremsstrahlung leads to broadening of the radiation pattern and a slower decay of the spectrum at the cut-off frequency than the conventional synchrotron emission. Possible implications of these features for air shower radio emission are discussed. [source]

    Magnetic jets from swirling discs

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
    D. Lynden-Bell
    ABSTRACT A broad swathe of astrophysical phenomena, ranging from tubular planetary nebulae through Herbig,Haro objects, radio galaxy and quasar emissions to gamma-ray bursts and perhaps high-energy cosmic rays, may be driven by magnetically dominated jets emanating from accretion discs. We give a self-contained account of the analytic theory of non-relativistic magnetically dominated jets wound up by a swirling disc and making a magnetic cavity in a background medium of any prescribed pressure, p(z). We solve the time-dependent problem for any specified distribution of magnetic flux P(R, 0) emerging from the disc at z= 0, with any specified disc angular velocity ,d(R). The physics required to do this involves only the freezing of the lines of force to the conducting medium and the principle of minimum energy. In a constant pressure environment, the magnetically dominated cavity is highly collimated and advances along the axis at a constant speed closely related to the maximum circular velocity of the accretion disc. Even within the cavity the field is strongly concentrated towards the axis. The twist in the jet field ,B,,/,|Bz|, is close to and the width of the jet decreases upwards. By contrast, when the background pressure falls off with height with powers approaching z,4, the head of the jet accelerates strongly and the twist of the jet is much smaller. The width increases to give an almost conical magnetic cavity with apex at the source. Such a regime may be responsible for some of the longest strongly collimated jets. When the background pressure falls off faster than z,4, there are no quasi-static configurations of well-twisted fields and the pressure confinement is replaced by a dynamic effective pressure or a relativistic expansion. In the regimes with rapid acceleration, the outgoing and incoming fields linking the twist back to the source are almost anti-parallel so there is a possibility that magnetic reconnections may break up the jet into a series of magnetic ,smoke-rings' travelling out along the axis. [source]

    On active galactic nuclei as sources of ultra-high energy cosmic rays

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008
    M. R. George
    ABSTRACT We measure the correlation between sky coordinates of the Swift Burst Alert Telescope (BAT) catalogue of active galactic nuclei (AGN) with the arrival directions of the highest energy cosmic rays detected by the Auger Observatory. The statistically complete, hard X-ray catalogue helps to distinguish between AGN and other source candidates that follow the distribution of local large-scale structure. The positions of the full catalogue are marginally uncorrelated with the cosmic ray arrival directions, but when weighted by their hard X-ray flux, AGN within 100 Mpc are correlated at a significance level of 98 per cent. This correlation sharply decreases for sources beyond ,100 Mpc, suggestive of a GZK suppression. We discuss the implications for determining the mechanism that accelerates particles to these extreme energies in excess of 1019 eV. [source]

    MAGIC J0616+225 as delayed TeV emission of cosmic rays diffusing from the supernova remnant IC 443

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008
    Diego F. Torres
    ABSTRACT We present a theoretical model that explains the high-energy phenomenology of the neighbourhood of the supernova remnant IC 443, as observed with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope and the Energetic Gamma-Ray Experiment Telescope (EGRET). We interpret MAGIC J0616+225 as delayed TeV emission of cosmic rays diffusing from IC 443 and interacting with a known cloud located at a distance of about 20 pc in the foreground of the remnant. This scenario naturally explains the displacement between EGRET and MAGIC sources, their fluxes, and their spectra. We compare this model with others recently presented, and discuss how it can be tested with observations by the Gamma-ray Large Area Space Telescope. [source]

    Strong signature of the active Sun in 100 years of terrestrial insolation data

    ANNALEN DER PHYSIK, Issue 6 2010
    W. Weber
    Abstract Terrestrial solar irradiance data of the Smithsonian Astrophysical Observatory from 1905 to 1954 and of Mauna Loa Observatory from 1958 to 2008 are analyzed. The analysis shows that, with changing solar activity, the atmosphere modifies the solar irradiance on the percentage level, in all likelihood via cosmic ray intensity variations produced by the active sun. The analysis strongly suggests that cosmic rays cause a large part of the atmospheric aerosols. These aerosols show specific absorption and scattering properties due to an inner structure of hydrated ionic centers, most probably of O2 - and O2+ produced by the cosmic rays. [source]

    Tidal dynamics of relativistic flows near black holes

    ANNALEN DER PHYSIK, Issue 5 2005
    C. Chicone
    Abstract We point out novel consequences of general relativity involving tidal dynamics of ultrarelativistic relative motion. Specifically, we use the generalized Jacobi equation and its extension to study the force-free dynamics of relativistic flows near a massive rotating source. We show that along the rotation axis of the gravitational source, relativistic tidal effects strongly decelerate an initially ultrarelativistic flow with respect to the ambient medium, contrary to Newtonian expectations. Moreover, an initially ultrarelativistic flow perpendicular to the axis of rotation is strongly accelerated by the relativistic tidal forces. The astrophysical implications of these results for jets and ultrahigh energy cosmic rays are briefly mentioned. [source]

    The origin of our galactic magnetic field

    ASTRONOMISCHE NACHRICHTEN, Issue 1 2010
    R.M. Kulsrud
    Abstract A serious difficulty with the standard alpha-omega theory of the origin of galactic magnetic fields involves the question of flux expulsion. This is intimately related to flux freezing. The alpha-omega theory is shown in the context of the giant superbubble explosions that have a large impact on the physics of the interstellar medium. It is shown that superbubbles alone can duplicate the processes of the alpha-omega dynamo and produce exponential growth of the galactic magnetic field. The possibility of the blow-out of pieces of the magnetic field is discussed and it is shown that they have the potential to solve the flux-expulsion problem. However, such an explanation must lead to apparent ,gaps' in the field in the galactic disc. These gaps are probably unavoidable in any dynamo theory and should have important observable consequences, one of which is an explanation for the escape of cosmic rays from the disc (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The interstellar magnetic field near the Galactic center

    ASTRONOMISCHE NACHRICHTEN, Issue 1 2010
    K. Ferričre
    Abstract We review the current observational knowledge of the interstellar magnetic field within ,150 pc ofthe Galactic center. We also discuss the various theoretical scenarios that have been put forward to explain the existing observations. Our critical overview leads to two important conclusions: (1) The interstellar magnetic field near the GC is approximately poloidal on average in the diffuse intercloud medium and approximately horizontal in dense interstellar clouds. (2) In the general intercloud medium, the field is relatively weak and probably close to equipartition with cosmic rays (B , (6,20) , G), but there exist a number of localized filaments where the field is much stronger (some filaments could possibly have B , 1 mG). In dense interstellar clouds, the field is probably rather strong, with typical values ranging between a few 0.1 mG and a few mG (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Transport of cosmic rays in the nearby starburst galaxy NGC 253,

    ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
    V. Heesen
    Abstract Radio halos require the coexistence of extra-planar cosmic rays and magnetic fields. Because cosmic rays are injected and accelerated by processes related to star formation in the disk, they have to be transported from the disk into the halo. A vertical large-scale magnetic field can significantly enhance this transport. We observed NGC 253 using radio continuum polarimetry with the Effelsberg and VLA telescopes. The radio halo of NGC 253 has a dumbbell shape with the smallest vertical extension near the center. With an estimate for the electron lifetime, we measured the cosmic-ray bulk speed as 300 ± 30 km s,1 which is constant over the extent of the disk. This shows the presence of a "disk wind" in NGC 253. We propose that the large-scale magnetic field is the superposition of a disk (r, ,) and halo (r, z) component. The disk field is an inward-pointing spiral with even parity. The conical (even) halo field appears in projection as an X-shaped structure, as observed in other edge-on galaxies. Interaction by compression in the walls of the superbubbles may explain the observed alignment between the halo field and the lobes of hot H, and soft X-ray emitting gas. The disk wind is a good candidate for the transport of small-scale helical fields, required for efficient dynamo action, and as a source for the neutral hydrogen observed in the halo (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Environment and luminosity of supernova remnants

    ASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006
    L. K. Hunt
    Abstract The explosion of supernovae and the evolution of their remnants (SNRs) accelerate cosmic rays over a vast range of timescales. Magnetic fields can be investigated indirectly through one of the observational signatures of this acceleration, namely radio synchrotron emission. With the aim of better understanding the role of the magnetic field in supernova evolution, we explore the variation of SNR radio luminosities with physical conditions in the surrounding interstellar medium. With a data set that comprises more than 90 individual SNRs in 10 galaxies, and a range of 3000 in ISM density and 104 in radio synchrotron luminosity, we find a significant correlation between the two quantities. The observed trends support the hypothesis that adiabatic compression of magnetic fields by itself is insuf.cient to explain the radio emission of the brighter and more luminous in SNRs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Magnetic fields in halos of spiral galaxies

    ASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006
    R.-J. Dettmar
    Abstract Observations of magnetic fields in halos of edge-on disk galaxies are discussed in relation to the interstellar disk-halo interface in disk galaxies. The distribution of extra-planar diffuse ionized gas correlates on local and global scales with cosmic rays and magnetic fields as inferred from observations of the non-thermal radio continuum radiation and its polarisation. From the polarisation a large-scale and well-ordered magnetic field in these gaseous halos can be deduced. For several objects a significant poloidal component of the halo field is likely. These observations indicate the presence of physical processes which generate and maintain magnetic fields on galactic scales. The importance of differential rotation of the gaseous halos for such processes is briefly discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The Granada workshop on High Redshift Radio Galaxies: An overview

    ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006
    H. J. A. Röttgering
    Abstract The Granada workshop on High Redshift Radio Galaxies (HzRGs) gave an excellent overview of the progress that has been made in this field during the last 3 years. Here we briefly review some of the results, with an emphasis on what studies of HzRGs can teach us about the formation and evolution of massive galaxies, clusters and active galactic nuclei (AGN). Of great relevance for this workshop are scenarios that describe certain aspects of the evolution of radio galaxies, including (i) the sequence of events after merging of galaxies that ultimately lead to extended powerful radio sources and (ii) the mass assembly and virialization of the hosting massive galaxies and their associated (proto-)clusters. Furthermore, I briefly discuss two projects that are important for a further understanding of AGN and high redshift radio galaxies. First, using the MIDI instrument mounted on the VLT Interferometer, the dusty tori of nearby AGN can be studied in the range of 8,13 micron at high angular resolution. The first result on the nearby AGN NGC 1068 as presented by Jaffe et al. (2004) indicated the presence of a hot (T > 800 K), compact (,1 pc) component, possible identified with the base of the jet and a warm (270 K), well-resolved (3 × 4 pc) component associated with the alleged torus. Second, LOFAR is a new low frequency radio telescope that is currently being build in the Netherlands and is expected to be operational in 2008. With 50 stations spread over an area of 100 km in diameter, its resolution and sensitivity will be unprecedented in the frequency range 10,240 MHz. LOFAR will be a unique instrument that will impact a broad range of astrophysical topics varying from the epoch of reionisation, to gamma ray bursts and cosmic rays. Surveys with LOFAR will be of paramount importance for studies of HzRGs: It will enable (i) defining samples of radio galaxies with redshifts higher than 6, (ii) observations of starbursting galaxies in proto-clusters, and (iii) mapping out the low-frequency radio emission of virtually all northern radio-loud AGN in revolutionary detail. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Clues to cosmic rays

    ASTRONOMY & GEOPHYSICS, Issue 6 2009
    Article first published online: 23 NOV 200
    No abstract is available for this article. [source]

    Catching the highest energy cosmic rays

    ASTRONOMY & GEOPHYSICS, Issue 2 2009
    Alan A Watson FRS
    First page of article [source]

    Ultra-high-energy cosmic rays tracked to sources

    ASTRONOMY & GEOPHYSICS, Issue 6 2007
    Article first published online: 14 NOV 200
    Active galactic nuclei are the most likely sources of ultra-high-energy cosmic rays, according to a map of their points of origin made by the Pierre Auger Collaboration. [source]