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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Cosmic ray drift, shock wave acceleration and the anomalous component of cosmic rays

A model of the anomalous component of the quiet-time cosmic ray flux is presented in which ex-interstellar neutral particles are accelerated continuously in the polar regions of the solar-wind termination shock, and then drift into the equatorial regions of the inner heliosphere. The observed solar-cycle variations, radial gradient, and apparent latitude gradient of the anomalous component are a natural consequence of this model.

Pesses, M. E.↗
NASA NTRS1981

Cosmic ray drift, shock wave acceleration, and the anomalous component of cosmic rays

A model of the anomalous component of the quiet-time cosmic ray flux is presented in which ex-interstellar neutral particles are accelerated continuously in the polar regions of the solar-wind termination shock and then drift into the equatorial regions of the inner heliosphere. The observed solar-cycle variations, radial gradient, and apparent latitude gradient of the anomalous component are a natural consequence of this model.

Pesses, M. E.↗
NASA NTRS2023

The High Energy X-Ray Probe (HEX-P): Galactic PeVatrons, Star Clusters, Superbubbles, Microquasar Jets, and Gamma-Ray Binaries

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10"FWHM) and broad spectral coverage (0.2--80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. With the recent discoveries of over 40 ultra-high-energy gamma-ray sources (detected above 100 TeV) and neutrino emission in the Galactic Plane, we have entered a new era of multi-messenger astrophysics facing the exciting reality of Galactic PeVatrons. In the next decade, as more Galactic PeVatrons and TeV gamma-ray sources are expected to be discovered, the identification of their acceleration and emission mechanisms will be the most pressing issue in both particle and high-energy astrophysics. In this paper, along with its companion papers (Reynolds et al. 2023, Mori et al. 2023), we will present that HEX-P is uniquely suited to address important problems in various cosmic-ray accelerators, including Galactic PeVatrons, through investigating synchrotron X-ray emission of TeV--PeV electrons produced by both leptonic and hadronic processes. For Galactic PeVatron candidates and other TeV gamma-ray sources, HEX-P can fill in a large gap in the spectral-energy distributions (SEDs) of many objects observed in radio, soft X-rays, and gamma rays, constraining the maximum energies to which electrons can be accelerated, with implications for the nature of the Galactic PeVatrons and their contributions to the spectrum of Galactic cosmic rays beyond the knee at $\sim3$ PeV. In particular, X-ray observation with HEX-P and TeV observation with CTA will provide the most powerful multi-messenger diagnostics to identify Galactic PeVatrons and explore a variety of astrophysical shock mechanisms. We present simulations of each class of Galactic TeV--PeV sources, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of Galactic cosmic-ray accelerators. In addition, we discuss HEX-P’s unique and complementary roles to upcoming gamma-ray and neutrino observatories in the 2030s.

particle accelerators↗
NASA NTRS1989

Effect of re-acceleration on cosmic ray components

Reacceleration of cosmic rays in interstellar space has been studied in detail in order to examine the behavior of the ratios of secondary to primary nuclei in cosmic radiation. It is found that modest acceleration in a confinement region, where particles escape more freely at high energies, provides a better fit to the observed data. The effect of reacceleration on the spectral shape of proton and helium components of cosmic rays has been studied. The examination of two different models has shown that reacceleration provides a poor fit to the observed proton data.

Stephens, S. A.↗
NASA NTRS1986

Coronal and interplanetary propagation, interplanetary acceleration, cosmic-ray observations by deep space network and anomalous component

The purpose is to provide an overview of the contributions presented in sessions SH3, SH1.5, SH4.6 and SH4.7 of the 19th International Cosmic Ray Conference. These contributed papers indicate that steady progress continues to be made in both the observational and the theoretical aspects of the transport and acceleration of energetic charged particles in the heliosphere. Studies of solar and interplanetary particles have placed emphasis on particle directional distributions in relation to pitch-angle scattering and magnetic focusing, on the rigidity and spatial dependence of the mean free path, and on new propagation regimes in the inner and outer heliosphere. Coronal propagation appears in need of correlative multi-spacecraft studies in association with detailed observation of the flare process and coronal magnetic structures. Interplanetary acceleration has now gone into a consolidation phase, with theories being worked out in detail and checked against observation.

Ng, C. K.↗
NASA NTRS1985

Acceleration of cosmic rays in supernova-remnants

It is commonly accepted that supernova-explosions are the dominant source of cosmic rays up to an energy of 10 to the 14th power eV/nucleon. Moreover, these high energy particles provide a major contribution to the energy density of the interstellar medium (ISM) and should therefore be included in calculations of interstellar dynamic phenomena. For the following the first order Fermi mechanism in shock waves are considered to be the main acceleration mechanism. The influence of this process is twofold; first, if the process is efficient (and in fact this is the cas) it will modify the dynamics and evolution of a supernova-remnant (SNR), and secondly, the existence of a significant high energy component changes the overall picture of the ISM. The complexity of the underlying physics prevented detailed investigations of the full non-linear selfconsistent problem. For example, in the context of the energy balance of the ISM it has not been investigated how much energy of a SN-explosion can be transfered to cosmic rays in a time-dependent selfconsistent model. Nevertheless, a lot of progress was made on many aspects of the acceleration mechanism.

Dorfi, E. A.↗
NASA NTRS2002

A Study of the Non-Thermal X-Ray Emission of Shell-Type Supernova Remnants

The term of the second year of the award is the period from March 15, 2001 to March 14, 2002. As was the specified goal of the second year, we analyzed the spatial and spectral X-ray data for several young supernova remnants. I published a paper about an analysis of the ROSAT, ASCA, and RXTE data for the supernova remnant SN 1006. A copy of this paper is enclosed. As described in the paper, we believe that we accurately modeled the nonthermal X-ray emission from the remnant. The results of this analysis are used to infer properties about the cosmic rays accelerated in the remnant and to argue that the strength of the magnetic field in the remnant is considerably larger than the value of about 10 micro G reported elsewhere. The results were presented at the August 2001 International Cosmic Ray Conference in Hamburg, German),. I began analyzing new Chandra X-ray data for SN 1006. This analysis will yield the first measure of the strength of the magnetic field in the remnant for the first time. Preliminary results support our previous conclusion that the magnetic field strength in the remnant is much larger than 10 micro G. The field strength seems to be about the strength expected based on an equipartition calculation. The result supports recent models that describe the how the shock structure is influenced by the efficient acceleration of cosmic rays. This work will be presented at the April 2002 High Energy Astrophysics Division meeting in Albuquerque and published this summer. A copy of the abstract for the talk is enclosed. I began studying new Chandra X-ray data for the supernova remnant Cas A. The results of this work show that the forward shock is a region where cosmic-ray electrons are accelerated, which is consistent with theoretical expectations. The work was presented at the September 2001 Two Years of Science with Chandra symposium in Washington, DC. A copy of the poster paper is enclosed. Dr. Thomas Pannuti, whose research work is supported by the award, analyzed ROSAT, ASCA, and RXTE data for the supernova remnant G347.3-0.5. The results show for the first time that thermal X-ray emission is produced in the remnant. As expected, the thermal emission is consistent with a model in which the remnant is expanding into a very low density environment. The results also provide an accurate description of the nonthermal emission from the remnant. Dr. Pannuti presented this work at several conferences. A copy of the paper for the proceedings of the August 2001 Neutron Stars in Supernova Remnants symposium in enclosed. The work will be submitted to the Astrophysical Journal in the next few months.

Allen, Glenn E.↗
NASA NTRS1974

Possible evidence for structured acceleration of cosmic rays on a galactic scale from recent gamma-ray observations

Recent data from SAS-2 on the galactic gamma-ray line flux as a function of longitude reveal a broad maximum in the region below 30 deg. These data, as unfolded here, imply that the low-energy (1-10 GeV) galactic cosmic-ray flux varies with the radial distance from the galactic center and is about an order of magnitude higher than the local value in a toroidal region for radial distances between 4 and 5 kpc. We further show that this enhancement can be plausibly accounted for by Fermi acceleration and compression caused by a hydrodynamic shock driven by the expanding gas in the 3-kpc arm and invoked in some versions of galactic structure theory.

Stecker, F. W.↗
NASA NTRS1981

Scaling from Jupiter to pulsar and the acceleration of cosmic ray particles by pulsars

The total energy output per second from the 73 known pulsars is estimated. By following the principle of similitude (Rayleigh, 1915), an expression is derived for the energy generated by a rotating magnetized celestial body, and the dipole moment of the body is related linearly with its angular momentum. The scaling constant of the two equations combined is determined, and then checked by comparing the deduced masses of the 73 pulsars with the theoretical limits for neutron stars. By using the scaling constant and deduced pulsar masses, the rates of acceleration of high-energy particles by pulsars, thence the energy output from pulsars, can be estimated. Results show that the Crab pulsar outshines all the others combined.

Fan, Y. C.↗
NASA NTRS1976

Cloud acceleration by cosmic rays in the vicinity of compact luminous objects

Nonrelativistic cosmic rays from a central source exert an outward pressure on the surrounding gas in a Seyfert nucleus or the envelope of a quasi-stellar object. This force is different from radiation pressure in that the momentum transfer to the gas is enhanced rather than reduced when the gas is ionized. Calculations are presented to show that particle energy flux comparable to observed photon luminosities will accelerate gas clouds as large as 100,000 solar masses to velocities on the order of 0.1c in the presence of a central mass of 100 million solar masses.

Eilek, J. A.↗
NASA NTRS1988

An overview of cosmic ray research - Composition, acceleration and propagation

An overview of cosmic ray (CR) research and its relationship to other areas of high-energy astrophysics is presented. Research being conducted on the composition of cosmic rays (CRs) is examined, including the study of the solar system 'template' for CRs, CR abundances at earth, solar energetic particles, the CR elements beyond zinc, and the study of electrons, positrons, antinuclei, and of isotopic composition of CRs. Research on the CR energy spectrum and anisotropy is briefly reviewed. The study of acceleration processes, particle confinement, and propagation of CRs is addressed. Finally, the investigation of source abundances in CRs is discussed.

Wefel, John P.↗
NASA NTRS1985

Pulsars as cosmic ray particle accelerators: Proton orbits

Proton orbits are calculated in the electromagnetic vacuum field of a magnetic point dipole rotating with its angular velocity omega perpendicular to its dipole moment mu by numerical integration of the Lorentz-Dirac equation. Trajectories are shown and discussed for various initial conditions. A critical surface is shown separating initial positions of protons which finally hit the pulsar in the polar region from those which finally recede to infinity.

Thielheim, K. O.↗
NASA NTRS1985

Pulsars as cosmic ray particle accelerators: Dynamics of electrons

The Lorentz-Dirac-equation with Landau approximation has been solved numerically for electrons in the electromagnetic field of a magnetic dipole rotating with the angular velocity omega perpendicular to its magnetic moment mu. Results are discussed with respect to electron orbits and energy development.

Thielheim, K. O.↗
DOE OSTI2025

New Tests of Low-Scale Quantum Gravity with Cosmic-Ray Collisions

Cosmic ray collisions at high center of mass energy could enable graviton and black hole production as expected in theories of low-scale quantum gravity, such as extra-dimensions, many species, or some versions of string theory. Here we propose three novel phenomenological tests of these theories. We first consider the collision of cosmic rays with ambient protons, electrons and photons in Active Galactic Nuclei (AGN), finding that high-energy neutrino data from the blazar TXS 0506+056 places a constraint on the fundamental scale of gravity of $M_f \gtrsim 0.3$ TeV, and future high-energy neutrino data could raise this bound to $M_f \gtrsim 200$ TeV. We then point out that collisions of pairs of cosmic rays could occur at a sizable rate in AGN where the accelerated cosmic rays are not collimated, or on supermassive black hole binaries. This consideration could potentially let us test unprecedented large fundamental scales of $M_f \gtrsim 2$ PeV. We further compute the corresponding thermal neutrino emission arising from the Hawking evaporation of black holes produced in cosmic ray collisions, finding a spectrum that clearly differs from that expected in meson decays. Finally, we speculate with an scenario which would produce high-energy neutrino and gamma-ray emission from regions in the sky where no multi-wavelength counterparts would be expected, via graviton propagation from a different brane, which then decays in our Universe.

Ettengruber, Manuel [IPhT, Saclay]↗
NASA NTRS1985

Ninteenth International Cosmic Ray Conference. SH Sessions, Volume 4

Papers submitted for presentation at the 19th International Cosmic Ray Conference are compiled. This volume covers solar and heliospheric phenomena, specifically, particle acceleration; cosmic ray compsotion, spectra, and anisotropy; propagation of solar and interplanetary energetic particles; solar-cycle modulation; and propagation of galactic particles in the heliosphere.

Jones, F. C.↗