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Lowell S Brown - One of the best experts on this subject based on the ideXlab platform.
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charged particle motion in a highly ionized plasma
Physics Reports, 2005Co-Authors: Lowell S Brown, Dean L Preston, Robert L SingletonAbstract:Abstract A recently introduced method utilizing dimensional continuation is employed to compute the Energy Loss Rate for a non-relativistic particle moving through a highly ionized plasma. No restriction is made on the charge, mass, or speed of this particle. It is, however, assumed that the plasma is not strongly coupled in the sense that the dimensionless plasma coupling parameter g = e 2 κ D / 4 π T is small, where κ D is the Debye wave number of the plasma. To leading and next-to-leading order in this coupling, d E / d x is of the generic form g 2 ln [ Cg 2 ] . The precise numerical coefficient out in front of the logarithm is well known. We compute the constant C under the logarithm exactly for arbitrary particle speeds. Our exact results differ from approximations given in the literature. The differences are in the range of 20% for cases relevant to inertial confinement fusion experiments. The same method is also employed to compute the Rate of momentum Loss for a projectile moving in a plasma, and the Rate at which two plasmas at different temperatures come into thermal equilibrium. Again these calculations are done precisely to the order given above. The Loss Rates of Energy and momentum uniquely define a Fokker–Planck equation that describes particle motion in the plasma. The coefficients determined in this way are thus well-defined, contain no arbitrary parameters or cutoffs, and are accuRate to the order described. This Fokker–Planck equation describes the straggling—the spreading in the longitudinal position of a group of particles with a common initial velocity and position—and the transverse diffusion of a beam of particles. It should be emphasized that our work does not involve a model, but rather it is a precisely defined evaluation of the leading terms in a well-defined perturbation theory.
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charged particle motion in a highly ionized plasma
arXiv: Plasma Physics, 2005Co-Authors: Lowell S Brown, Dean L Preston, Robert L SingletonAbstract:A recently introduced method utilizing dimensional continuation is employed to compute the Energy Loss Rate for a non-relativistic particle moving through a highly ionized plasma. No restriction is made on the charge, mass, or speed of this particle. It is, however, assumed that the plasma is not strongly coupled in the sense that the dimensionless plasma coupling parameter g=e^2\kappa_D/ 4\pi T is small, where \kappa_D is the Debye wave number of the plasma. To leading and next-to-leading order in this coupling, dE/dx is of the generic form g^2 \ln[C g^2]. The precise numerical coefficient out in front of the logarithm is well known. We compute the constant C under the logarithm exactly for arbitrary particle speeds. Our exact results differ from approximations given in the literature. The differences are in the range of 20% for cases relevant to inertial confinement fusion experiments. The same method is also employed to compute the Rate of momentum Loss for a projectile moving in a plasma, and the Rate at which two plasmas at different temperatures come into thermal equilibrium. Again these calculations are done precisely to the order given above. The Loss Rates of Energy and momentum uniquely define a Fokker-Planck equation that describes particle motion in the plasma. The coefficients determined in this way are thus well-defined, contain no arbitrary parameters or cutoffs, and are accuRate to the order described. This Fokker-Planck equation describes the longitudinal straggling and the transverse diffusion of a beam of particles. It should be emphasized that our work does not involve a model, but rather it is a precisely defined evaluation of the leading terms in a well-defined perturbation theory.
D. Bastieri - One of the best experts on this subject based on the ideXlab platform.
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fermi and swift observations of grb 190114c tracing the evolution of high Energy emission from prompt to afterglow
The Astrophysical Journal, 2020Co-Authors: M Ajello, D. Bastieri, M Arimoto, M Axelsson, L Baldini, G Barbiellini, R BellazziniAbstract:We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. The early-time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to constrain the transition from internal shock to external shock dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment and find that high-Energy photons observed by Fermi LAT are in tension with the theoretical maximum Energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron Energy are further compounded by the detection of very high Energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT Energy range, an acceleration mechanism that imparts Energy to the particles at a Rate that is faster than the electron synchrotron Energy Loss Rate, or revisions of the fundamental assumptions used in estimating the maximum photon Energy attainable through the synchrotron process.
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The First Fermi Large Area Telescope Catalog of Gamma-ray Pulsars
Astrophysical Journal Supplement, 2010Co-Authors: A. A. Abdo, Markus Ackermann, Marco Ajello, W. B. Atwood, Magnus Axelsson, Luca Baldini, Jean Ballet, Guido Barbiellini, M. G. Baring, D. BastieriAbstract:The dramatic increase in the number of known gamma-ray pulsars since the launch of the Fermi Gamma-ray Space Telescope (formerly GLAST) offers the first opportunity to study a population of these high-Energy objects. This catalog summarizes 46 high-confidence pulsed detections using the first six months of data taken by the Large Area Telescope (LAT), Fermi's main instrument. Sixteen previously unknown pulsars were discovered by searching for pulsed signals at the positions of bright gamma-ray sources seen with the LAT, or at the positions of objects suspected to be neutron stars based on observations at other wavelengths. Pulsed gamma-ray emission was discovered from twenty-four known pulsars by using ephemerides (timing solutions) derived from monitoring radio pulsars. Eight of these new gamma-ray pulsars are millisecond pulsars. The pulsed Energy spectra can be described by a power law with an exponential cutoff, with cutoff energies in the range 1 to 5 GeV. The rotational Energy Loss Rate (\dot{E}) of these neutron stars spans 5 decades, from ~3x10^{33} erg/s to 5x10^{38} erg/s, and the apparent efficiencies for conversion to gamma-ray emission range from ~0.1% to unity, although distance uncertainties complicate efficiency estimates. The pulse shapes show substantial diversity, but roughly 75% of the gamma-ray pulse profiles have two peaks, sepaRated by >0.2 of rotational phase. For most of the pulsars, gamma-ray emission appears to come mainly from the outer magnetosphere, while polar-cap emission remains plausible for a remaining few. Finally, these discoveries suggest that gamma-ray-selected young pulsars are born at a Rate comparable to that of their radio-selected cousins and that the birthRate of all young gamma-ray-detected pulsars is a substantial fraction of the expected Galactic supernova Rate.
István Nándori - One of the best experts on this subject based on the ideXlab platform.
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Neutrino Pair Cerenkov Radiation for Tachyonic Neutrinos
Advances in High Energy Physics, 2017Co-Authors: Ulrich D. Jentschura, István NándoriAbstract:The emission of a charged light lepton pair by a superluminal neutrino has been identified as a major factor in the Energy Loss of highly energetic neutrinos. The observation of PeV neutrinos by IceCube implies their stability against lepton pair Cerenkov radiation. Under the assumption of a Lorentz-violating dispersion relation for highly energetic superluminal neutrinos, one may thus constrain the Lorentz-violating parameters. A kinematically different situation arises when one assumes a Lorentz-covariant, space-like dispersion relation for hypothetical tachyonic neutrinos, as an alternative to Lorentz-violating theories. We here discuss a hitherto neglected decay process, where a highly energetic tachyonic neutrino may emit other (space-like, tachyonic) neutrino pairs. We find that the space-like dispersion relation implies the absence of a threshold for the production of a tachyonic neutrino-antineutrino pair, thus leading to the dominant additional Energy Loss mechanism for an oncoming tachyonic neutrino in the medium-Energy domain. Surprisingly, the small absolute values of the decay Rate and Energy Loss Rate in the tachyonic model imply that these models, in contrast to the Lorentz-violating theories, are not pressured by the cosmic PeV neutrinos registered by the IceCube collaboration.
Gordon A Emslie - One of the best experts on this subject based on the ideXlab platform.
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suppression of parallel transport in turbulent magnetized plasmas and its impact on the non thermal and thermal aspects of solar flares
The Astrophysical Journal, 2016Co-Authors: N H Bian, Eduard P Kontar, Gordon A EmslieAbstract:The transport of the Energy contained in electrons, both thermal and suprathermal, in solar flares plays a key role in our understanding of many aspects of the flare phenomenon, from the spatial distribution of hard X-ray emission to global energetics. Motivated by recent RHESSI observations that point to the existence of a mechanism that confines electrons to the coronal parts of flare loops more effectively than Coulomb collisions, we here consider the impact of pitch-angle scattering off turbulent magnetic fluctuations on the parallel transport of electrons in flaring coronal loops. It is shown that the presence of such a scattering mechanism in addition to Coulomb collisional scattering can significantly reduce the parallel thermal and electrical conductivities relative to their collisional values. We provide illustrative expressions for the resulting thermoelectric coefficients that relate the thermal flux and electrical current density to the temperature gradient and the applied electric field. We then evaluate the effect of these modified transport coefficients on the flare coronal temperature that can be attained, on the post-impulsive-phase cooling of heated coronal plasma, and on the importance of the beam-neutralizing return current on both ambient heating and the Energy Loss Rate of acceleRated electrons. We also discuss the possible ways in which anomalous transport processes have an impact on the required overall Energy associated with acceleRated electrons in solar flares.
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empirical determination of the Energy Loss Rate of acceleRated electrons in a well observed solar flare
The Astrophysical Journal, 2012Co-Authors: Gabriele Torre, Anna Maria Massone, Nicola Pinamonti, Gordon A Emslie, Jingnan Guo, Michele PianaAbstract:We present electron images of an extended solar flare source, deduced from RHESSI hard X-ray imaging spectroscopy data. We apply the electron continuity equation to these maps in order to determine empirically the form of the Energy Loss Rate for the bremsstrahlung-emitting electrons. We show that this form is consistent with an Energy transport model involving Coulomb collisions in a target with a temperature of about 2 × 107 K, with a continuous injection of fresh deka-keV electrons at a Rate of approximately 10–2 electrons s–1 per ambient electron.
Yan Dong - One of the best experts on this subject based on the ideXlab platform.
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dynamics of descending knots in a solar prominence and their possible contributions to the heating of the local corona
The Astrophysical Journal, 2020Co-Authors: Bo Yang, Yan DongAbstract:The knots in solar prominences are often observed to fall with nearly constant velocity, but the associated physical mechanism is currently not well understood. In this letter, we presented a prominence observed by New Vacuum Solar Telescope (NVST) in H-alpha wavelength. Knots that rose within the prominence appear to have been preferentially located at higher altitude, whereas those that fell were found throughout the entire prominence structure. The descending speed of the knots near the solar surface was higher than that far away from the solar surface. We noted that the knots near the solar surface may run along a set of coronal loops observed from the Atmospheric Imaging Assembly. Elsewhere, the majority of knots are interpreted to have descended across more horizontal magnetic field with a nearly constant speed. This lack of acceleration indicates that the libeRated gravitational potential Energy may not manifest as an increase in kinetic Energy. Assuming instead that the descending knots were capable of exciting Alfven waves that could then dissipate within the local corona, the gravitational potential Energy of the knots may have been converted into thermal Energy. Assuming a perfectly elastic system, we therefore estimate that the gravitational Energy Loss Rate of these observed knots amounts to 1/2000 of that required to heat the entire quiet-Sun, increasing to 1/320 when considering possibly further downward motions of the knots having disappeared in the H-alpha observations. This result suggests such a mechanism may contribute to the heating of the corona local to these prominences.