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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2021

Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1

Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability, and convenient physical parameters (close distance, high inclination, and small orbital separation), which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems for understanding accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ∼0.68–0.78 and ∼0.36–0.52, which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period timescale using a partially covered power law continuum with a Fermi-Dirac cutoff to model the continuum and local absorption. We are able to confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We were not able to confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ∼0.36–0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion and photoionisation wakes in the system, and our variable line of sight through this structure.

C. M. Diez↗

NASA NTRS1991

Magnetic correlations in La(2-x)Sr(x)CuO4 from NQR relaxation and specific heat

La-139 and Cu-63 Nuclear Quadrupole Resonance (NQR) relaxation measurements in La(2-x)Sr(x)CuO4 for x ranging from 0 up to 0.3, with particular emphasis on the effect of doping on the Cu(2+) magnetic correlations and dynamics, are reviewed. In the low doping limit, x less than or equal to 0.05, the results can be interpreted consistently in terms of a simple phenomenological 'two-fluids' model whereby the effect of thermally-activated mobile O(2p) holes is the one of disrupting locally the Cu(2+) spin correlations. For x greater than or equal to 0.1, the results indicate the onset, as T approaches T(sub c)(+), of a strong coupling between Cu(2+) spins and the Fermi liquid of O(2p) holes leading to the apparent disappearance of localized Cu(2+) moment in connection with the opening of a superconducting gap.

Borsa, F.↗

NASA NTRS1985

Cosmic-ray transport in the galactic magnetosphere

It is advantageous to regard cosmic rays as the constitutent particles of the Galactic radiation belts and cosmic ray energization as a consequence of inward radial diffusion in the quasi-dipolar Galactic magnetosphere. This process occurs in addition to Fermi acceleration. The purpose of this work is to explore a magnetospheric explanation for the elevation of Galactic charged particles to cosmic ray energies. The magnetosphere that is of interest in this context is not a planetary magnetosphere but a galactic magnetosphere entirely analogous to those inferred from radio observations of distant galaxies. It is the magnetosphere of the Milky Way. Cosmic rays are (by this interpretation) the charged particles that constitute the radiation belts of the Galactic magnetosphere. Thus, the mechanism by which charged particles attain cosmic-ray energies is presumable the mechanism by which radiation-belt particles attain high energies in more familiar magnetosphere, i.e., the radial diffusion associated with magnetic disturbances that contain spectral power resonant with the azimuthal drift of the particles.

Schulz, M.↗

NASA NTRS2019

Source of the Bursty Bulk Flow Diffuse Aurora: Electrostatic Cyclotron Harmonic and Whistler Waves in the Coupling of Bursty Bulk Flows to Auroral Precipitation

Electron cyclotron harmonic (ECH) and whistler chorus waves are recognized as the two mechanisms responsible for the resonant wave‐particle interactions necessary to precipitate plasma sheet electrons into the ionosphere, producing the diffuse Aurora. Previous work has demonstrated ECH waves dominate electron scattering at L shells >8, while whistler chorus dominates scattering at L shells L < 8. However, we ﬁnd from Time History of Events and Macroscale (THEMIS) Interactions during Substorms observations of fast ﬂows at L = 12 that oblique whistler chorus emissions play the dominant role in scattering electrons. Previous works have identiﬁed whistler‐mode waves within fast ﬂows that are produced by an electron temperature anisotropy Te,⊥/Te,||> 1, consistent with electron betatron acceleration. Here, however, we ﬁnd whistler chorus emissions throughout an interval of fast ﬂows where Te,⊥/Te,||< 1. Parallel electron beams account for the enhanced parallel electron temperature and serve as the instability mechanism for the whistler chorus. The parallel electron beams and associated cigar‐shaped distributions are consistent with Fermi acceleration at dipolarizations in fast ﬂows. We demonstrate that the scattering efﬁciency of the whistler chorus exceeds that of ECH waves, which THEMIS also detects during the fast ﬂows. The obliquity of the whistler waves permits efﬁcient scattering of lower‐energy electrons into the diffuse aurora. We conclude that Fermi acceleration of electrons provides one important free‐energy source for the wave‐particle interactions responsible for coupling plasma sheet electrons into the diffuse aurora during substorm conditions.

Wendel, D. E.↗