scholarly journals Diagnosing cosmic ray modified shocks with H α polarimetry

2019 ◽  
Vol 489 (2) ◽  
pp. 2723-2731
Author(s):  
Jiro Shimoda ◽  
J Martin Laming
Keyword(s):  
Rest Frame ◽  
Cosmic Ray ◽  
Resonant Scattering ◽  
Shock Velocity ◽  
Polarization Direction ◽  
Exchange Reactions ◽  
Hydrogen Atoms ◽  
Shock Surface ◽  
Ram Pressure ◽  
Linearly Polarized

ABSTRACT A novel diagnostic of cosmic ray modified shocks by polarimetry of H α emissions is suggested. In a cosmic ray modified shock, the pressure of cosmic rays is sufficiently high compared to the upstream ram pressure to force the background plasma to decelerate (measured in the shock rest frame). Simultaneously, a fraction of the hydrogen atoms co-existing in the upstream plasma collide with the decelerated protons and undergo charge-exchange reactions. As a result, hydrogen atoms with the same bulk velocity of the decelerated protons are generated. We show that when the shock is observed from edge-on, the H α radiated by these upstream hydrogen atoms is linearly polarized with a sizable degree of a few per cent as a result of resonant scattering of Ly β. The polarization direction depends strongly on the velocity modification; the direction is parallel to the shock surface for the case of no modification, while the direction is parallel to the shock velocity for the case of a modified shock.

Foreshock ULF fluctuations near the Moon: THEMIS observations

2021 ◽  
Author(s):  
Anna Salohub ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Rest Frame ◽  
Low Frequency ◽  
Solar Wind Plasma ◽  
Turbulent Plasma ◽  
Bow Shock ◽  
Ulf Waves ◽  
The Moon ◽  
Shock Surface ◽  
The Earth

<p>The foreshock is a region filled with a turbulent plasma located upstream the Earth’s bow shock where interplanetary magnetic field (IMF) lines are connected to the bow shock surface. In this region, ultra-low frequency (ULF) waves are generated due to the interaction of the solar wind plasma with particles reflected from the bow shock back into the solar wind. It is assumed that excited waves grow and they are convected through the solar wind/foreshock, thus the inner spacecraft (close to the bow shock) would observe larger wave amplitudes than the outer (far from the bow shock) spacecraft. The paper presents a statistical analysis of excited ULF fluctuations observed simultaneously by two closely separated THEMIS spacecraft orbiting the Moon under a nearly radial IMF. We found that ULF fluctuations (in the plasma rest frame) can be characterized as a mixture of transverse and compressional modes with different properties at both locations. We discuss the growth and/or damping of ULF waves during their propagation.</p>

scholarly journals Control of the polarization direction of isolated attosecond pulses using inhomogeneous two-color fields

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Stephen Maina Njoroge ◽  
Hua Yuan ◽  
Kinyua Dickson ◽  
Qingbin Zhang ◽  
Pengfei Lan
Keyword(s):  
Polarization Direction ◽  
Relative Angle ◽  
Water Window ◽  
High Order Harmonic ◽  
Fundamental Pulse ◽  
Wide Range ◽  
Attosecond Pulses ◽  
Linearly Polarized ◽  
Window Region ◽  
And Control

AbstractWe theoretically demonstrate the control of the polarization direction of isolated attosecond pulses (IAPs) with inhomogeneous two-color fields synthesized by an 800-nm fundamental pulse and a 2000-nm control pulse having crossed linear polarizations. The results show that by using the temporally and spatially shaped field, the high-order harmonic generation (HHG) process can be efficiently controlled. An ultra-broad supercontinuum ranging from 150th to 400th harmonics which covers the water window region is generated. Such a supercontinuum supports the generation of a 64-as linearly polarized IAP, whose polarization direction is at about 45° with respect to the x axis. Moreover, we analyze the influence of the inhomogeneity parameters and the relative angle of the fundamental and control pulses on the IAP generation. It is shown that the polarization direction of the IAP can rotate in a wide range approximately from 8° to 90° relative to the x axis when the inhomogeneity parameters and the relative angle vary.

scholarly journals Balmer-dominated shocks in Tycho’s SNR: omnipresence of CRs

2017 ◽  
Vol 12 (S331) ◽  
pp. 248-253
Author(s):  
Sladjana Knežević ◽  
Ronald Läsker ◽  
Glenn van de Ven ◽  
Joan Font ◽  
John C. Raymond ◽  
...  
Keyword(s):  
Line Width ◽  
Cosmic Ray ◽  
Wide Field ◽  
Hydrogen Atoms ◽  
Narrow Line Width ◽  
Shock Region ◽  
Bayesian Evidence ◽  
Post Shock ◽  
Spurious Result ◽  
First Time

AbstractWe present wide-field, spatially and highly resolved spectroscopic observations of Balmer filaments in the northeastern rim of Tycho’s supernova remnant in order to investigate the signal of cosmic-ray (CR) acceleration. The spectra of Balmer-dominated shocks (BDSs) have characteristic narrow (FWHM ~ 10 km s−1) and broad (FWHM ~ 1000 km s−1) Hα components. CRs affect the Hα-line parameters: heating the cold neutrals in the interstellar medium results in broadening of the narrow Hα-line width beyond 20 km s−1, but also in reduction of the broad Hα-line width due to energy being removed from the protons in the post-shock region. For the first time we show that the width of the narrow Hα line, much larger than 20 km s−1, is not a resolution or geometric effect nor a spurious result of a neglected intermediate (FWHM ~ 100 km s−1) component resulting from hydrogen atoms undergoing charge exchange with warm protons in the broad-neutral precursor. Moreover, we show that a narrow line width ≫ 20 km s−1extends across the entire NE rim, implying CR acceleration is ubiquitous, and making it possible to relate its strength to locally varying shock conditions. Finally, we find several locations along the rim, where spectra are significantly better explained (based on Bayesian evidence) by inclusion of the intermediate component, with a width of 180 km s−1on average.

scholarly journals MUSEQuBES: calibrating the redshifts of Ly α emitters using stacked circumgalactic medium absorption profiles

2020 ◽  
Vol 496 (2) ◽  
pp. 1013-1022 ◽  
Author(s):  
Sowgat Muzahid ◽  
Joop Schaye ◽  
Raffaella Anna Marino ◽  
Sebastiano Cantalupo ◽  
Jarle Brinchmann ◽  
...  
Keyword(s):  
Average Velocity ◽  
Rest Frame ◽  
Main Sequence ◽  
Formation Rate ◽  
Resonant Scattering ◽  
Mass Scaling ◽  
Dust Extinction ◽  
Lyman Break Galaxies ◽  
Direct Measurements ◽  
Circumgalactic Medium

ABSTRACT Ly α emission lines are typically found to be redshifted with respect to the systemic redshifts of galaxies, likely due to resonant scattering of Ly α photons. Here, we measure the average velocity offset for a sample of 96 z ≈ 3.3 Ly α emitters (LAEs) with a median Ly α flux (luminosity) of ${\approx}10^{-17}~\rm erg~cm^{-2}~s^{-1}$ (${\approx}10^{42}~\rm erg~s^{-1}$) and a median star formation rate (SFR) of ≈1.3 $\rm M_{\odot }~yr^{-1}$ (not corrected for possible dust extinction), detected by the Multi-Unit Spectroscopic Explorer as part of our MUSEQuBES circumgalactic medium (CGM) survey. By postulating that the stacked CGM absorption profiles of these LAEs, probed by eight background quasars, must be centred on the systemic redshift, we measure an average velocity offset, Voffset = 171\pm 8 km s−1, between the Ly α emission peak and the systemic redshift. The observed Voffset is lower by factors of ≈1.4 and ≈2.6 compared to the velocity offsets measured for narrow-band-selected LAEs and Lyman break galaxies, respectively, which probe galaxies with higher masses and SFRs. Consistent with earlier studies based on direct measurements for individual objects, we find that the Voffset is correlated with the full width at half-maximum of the red peak of the Ly α line, and anticorrelated with the rest-frame equivalent width. Moreover, we find that Voffset is correlated with SFR with a sub-linear scaling relation, $V_{\rm offset}\propto \rm SFR^{0.16\pm 0.03}$. Adopting the mass scaling for main-sequence galaxies, such a relation suggests that Voffset scales with the circular velocity of the dark matter haloes hosting the LAEs.

scholarly journals A radiation belt of energetic protons located between Saturn and its rings

Science ◽  
2018 ◽  
Vol 362 (6410) ◽  
pp. eaat1962 ◽  
Author(s):  
E. Roussos ◽  
P. Kollmann ◽  
N. Krupp ◽  
A. Kotova ◽  
L. Regoli ◽  
...  
Keyword(s):  
Radiation Belt ◽  
Cosmic Ray ◽  
High Energy ◽  
Radiation Belts ◽  
Exchange Reactions ◽  
Dipole Magnetic Field ◽  
Imaging Instrument ◽  
Multiple Charge ◽  
Strong Dipole ◽  
Dense Atmosphere

Saturn has a sufficiently strong dipole magnetic field to trap high-energy charged particles and form radiation belts, which have been observed outside its rings. Whether stable radiation belts exist near the planet and inward of the rings was previously unknown. The Cassini spacecraft’s Magnetosphere Imaging Instrument obtained measurements of a radiation belt that lies just above Saturn’s dense atmosphere and is decoupled from the rest of the magnetosphere by the planet’s A- to C-rings. The belt extends across the D-ring and comprises protons produced through cosmic ray albedo neutron decay and multiple charge-exchange reactions. These protons are lost to atmospheric neutrals and D-ring dust. Strong proton depletions that map onto features on the D-ring indicate a highly structured and diverse dust environment near Saturn.

THE ZEROTH LAW OF THERMODYNAMICS OF THE PHOTON–HYDROGEN SYSTEM AND 21 cm COSMOLOGY

2009 ◽  
Vol 18 (13) ◽  
pp. 1943-1954 ◽  
Author(s):  
LI-ZHI FANG
Keyword(s):  
Thermal Equilibrium ◽  
Neutral Hydrogen ◽  
Resonant Scattering ◽  
Hydrogen Gas ◽  
Color Temperature ◽  
Local Thermal Equilibrium ◽  
Kinetic Temperature ◽  
Hydrogen Atoms ◽  
Thermal Equilibrium State ◽  
Field Coupling

A basic physical problem of 21 cm cosmology is the so-called Wouthuysen–Field coupling, which assumes that the resonant scattering of Lyα photons with neutral hydrogen atoms will lock the color temperature of the photon spectrum around the Lyα frequency to be equal to the kinetic temperature of hydrogen gas. This assumption is actually the zeroth thermodynamic law on the formation of the local statistically thermal equilibrium state of the photon–atom system. However, the time-dependent process of approaching a local statistically thermal equilibrium with the kinetic temperature has never been studied, as it needs to solve an integral–differential equation — the radiative transfer equation of the resonant scattering. Recently, with a state-of-the-art numerical method, the formation and evolution of the Wouthuysen–Field coupling has been systematically studied. This paper reviews the physical results, including the time scales of the onset of Wouthuysen–Field coupling, the profile of frequency distribution of photons in the state of local thermal equilibrium, the effects of the expansion of the universe, the Wouthuysen–Field coupling in an optical thick halo, etc.

EXCHANGE REACTIONS OF HYDROGEN ATOMS

1934 ◽  
Vol 56 (3) ◽  
pp. 750-750 ◽  
Author(s):  
Norris F. Hall ◽  
Everett Bowden ◽  
T. O. Jones
Keyword(s):  
Exchange Reactions ◽  
Hydrogen Atoms

Investigations of plasma-wall interaction by H alpha resonant scattering in the tokamak UNITOR

1982 ◽  
Vol 28 (2) ◽  
pp. 281-291 ◽  
Author(s):  
G. Reinhold ◽  
J. Hackmann ◽  
J. Uhlenbusch
Keyword(s):  
Density Distribution ◽  
Resonant Scattering ◽  
Background Plasma ◽  
Hydrogen Atoms ◽  
Plasma Parameters ◽  
Special Regard ◽  
Interaction Processes ◽  
Wall Interaction

The Hα resonant scattering diagnostics applied to the tokamak UNITOR is described. The measurements yield the density distribution of excited hydrogen atoms as a result of plasma-wall interaction processes and background plasma parameters. Special regard has been given to the influence of recycling processes.

Exchange reactions of olefins with deuterium oxide on ion-exchanged X-type zeolites

1971 ◽  
Vol 321 (1545) ◽  
pp. 259-273 ◽  
Keyword(s):  
Active Sites ◽  
Deuterium Oxide ◽  
Reaction Rates ◽  
Main Reaction ◽  
Exchange Reactions ◽  
Hydrogen Atoms ◽  
Carbonium Ion ◽  
Mass Spectrometric Technique ◽  
Carbonium Ions ◽  
Cation Charge

Reactions of propylene, ethylene, but-1-ene , isobutene and isobutane with D 2 O on ion-exchanged X-type zeolites have been followed by a mass spectrometric technique. Exchange was usually the main reaction but polymerization of olefins also occurred with some catalysts. All the hydrogen atoms in isobutene were exchanged at similar rates by a stepwise process but with propylene only five atoms were replaced. Exchange was complicated by simultaneous isomerization with but-1-ene. Isobutane reacted only at high temperatures but gave multiply exchanged products. The order of activity for exchange was isobutene ⪢ but-1-ene > propylene ⪢ ethylene, isobutane, and this order appeared to reflect the relative ease of formation of carbonium ions from the hydrocarbons. The character of the exchange reactions as well as the rates were in accord with mechanisms involving carbonium ion intermediates . The order of activity of the zeolites for the exchange of propylene was CeX, LaX > NiX, CuX, CoX > CaX > NaX and a correlation was found to exist between the apparent activation energy for exchange and a function of the cation charge. Reaction rates on NiX and CeX increased with increasing degree of ion-exchange and decreased with increasing amounts of D 2 O. There was evidence that in some cases the active sites were associated with acidic OH(OD) groups rather than the cations themselves.

Cosmic-ray nuclei up to 10 10 eV/u in the galaxy

1975 ◽  
Vol 277 (1270) ◽  
pp. 319-348 ◽  
Keyword(s):  
Cosmic Rays ◽  
Solar System ◽  
Cross Sections ◽  
Cosmic Ray ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
Hydrogen Atoms ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ionization Cross Sections

O f the nuclear cosmic rays arriving in the vicinity of Earth from interstellar space, more than 90% have energies less than 1010 eV /u.f Some effects of their modulation (including deceleration) in the Solar System are briefly discussed. The origin of particles at energies < 107 eV/u is still obscure. They could be due to stellar explosions or to solar emissions, or perhaps to interaction of interstellar gas with the solar wind. Between 108 and 1010 eV/u, the composition appears constant to ca. 30% within the statistics of available data. Cosmic rays traverse a mean path length of 6 g/cm 2 in a medium assumed to contain nine hydrogen atoms for each helium atom. Spallation reactions occurring in this medium result in enhancement of many cosmic-ray elements that are more scarce in the general abundances by several orders of magnitude. Cosmic-ray dwell time in the Galaxy seems to be < 107 years. The source composition of cosmic rays has been derived for elements with atomic numbers 1 ≤ Z ≤ 26. A comparison with abundances in the Solar System implies that the latter is richer in hydrogen and helium by a factor of ca. 20, in N and O by ca. 5, and in C by a factor of ca.2. Possible interpretations invoke (a) nucleosynthesis of cosmic rays in certain sources, e.g. supernovae, or (b) models of selective injection that depend, e.g. on ionization potentials or ionization cross sections. Calculated isotopic abundances of arriving cosmic rays are compared with the observed values now becoming available, and found to be in general agreement. Recent progress in probing the composition and spectrum of ultra-heavy nuclei is outlined.

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