Electrodynamic Structure of an Outer Gap Accelerator: Location of the Gap and the Gamma-ray Emission from the Crab Pulsar

We investigate a stationary pair production cascade in the outer magnetosphere of a spinning neutron star. The charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate curvature gamma-rays, some of which collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen the electric field, which is self-consistently solved together with the distribution functions of particles and gamma-rays. If no current is injected at neither of the boundaries of the accelerator, the gap is located around the conventional null surface, where the local Goldreich-Julian charge density vanishes. However, we first find that the gap position shifts outwards (or inwards) when particles are injected at the inner (or outer) boundary. Applying the theory to the Crab pulsar, we demonstrate that the pulsed TeV flux does not exceed the observational upper limit for moderate infrared photon density and that the gap should be located near to or outside of the conventional null surface so that the observed spectrum of pulsed GeV fluxes may be emitted via a curvature process. Some implications of the existence of a solution for a super Goldreich-Julian current are discussed.Comment: 17 pages, 12 figures, submitted to Ap

Nonlinear dynamo action in a precessing cylindrical container

It is numerically demonstrated by means of a magnetohydrodynamics (MHD) code that precession can trigger the dynamo effect in a cylindrical container. This result adds credit to the hypothesis that precession can be strong enough to be one of the sources of the dynamo action in some astrophysical bodies.Comment: 5 pages, 5 figures including subfigure

Kinematics of massive star ejecta in the Milky Way as traced by 26^26Al

Context. Massive stars form in groups and their winds and supernova explosions create superbubbles up to kpc in size. The fate of their ejecta is of vital importance for the dynamics of the interstellar medium, for chemical evolution models, and the chemical enrichment of galactic halos and the intergalactic medium. However, ejecta kinematics and the characteristic scales in space and time have not been explored in great detail beyond ~10 Ka. Aims: Through measurement of radioactive 26Al with its decay time constant at ~106 years, we aim to trace the kinematics of cumulative massive-star and supernova ejecta independent of the uncertain gas parameters over million-year time scales. Our goal is to identify the mixing time scale and the spatio-kinematics of such ejecta from the pc to kpc scale in our Milky Way. Methods: We use the SPI spectrometer on the INTEGRAL observatory and its observations along the Galactic ridge to trace the detailed line shape systematics of the 1808.63 keV gamma-ray line from 26Al decay. We determine line centroids and compare these to Doppler shift expectations from large-scale systematic rotation around the Galaxy centre, as observed in other Galactic objects. Results: We measure the radial velocities of gas traced by 26Al, averaged over the line of sight, as a function of Galactic longitude. We find substantially higher velocities than expected from Galactic rotation, the average bulk velocity being ~200 km s-1 larger than predicted from Galactic rotation. The observed radial velocity spread implies a Doppler broadening of the gamma-ray line that is consistent with our measurements of the overall line width. We can reproduce the observed characteristics with 26Al sources located along the inner spiral arms, when we add a global blow-out preference into the forward direction away from arms into the inter-arm region, as is expected when massive stars are offset towards the spiral-arm leading edge. With the known connection of superbubbles to the gaseous halo, this implies angular-momentum transfer in the disk-halo system and consequently also radial gas flows. The structure of the interstellar gas above the disk affects how ionizing radiation may escape and ionize intergalactic gas.Peer reviewe

Origin of magnetic moments in defective TiO2 single crystals

In this paper we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman-scattering, and electron spin resonance spectroscopy, a defect complex, \emph{i.e.} Ti$^{3+}$ ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a local (TiO$_{6-x}$) stretching Raman mode. We elucidate that Ti$^{3+}$ ions with one unpaired 3d electron provide the local magnetic moments.Comment: 4 pages, 4 figures, to be published at Phys. Rev.

Role of the exchange and correlation potential into calculating the x-ray absorption spectra of half-metallic alloys: the case of Mn and Cu K-edge XANES in Cu2_2MnM (M = Al, Sn, In) Heusler alloys

This work reports a theoretical study of the x-ray absorption near-edge structure spectra at both the Cu and the Mn K-edge in several Cu$_2$MnM (M= Al, Sn and In) Heusler alloys. Our results show that {\it ab-initio} single-channel multiple-scattering calculations are able of reproducing the experimental spectra. Moreover, an extensive discussion is presented concerning the role of the final state potential needed to reproduce the experimental data of these half-metallic alloys. In particular, the effects of the cluster-size and of the exchange and correlation potential needed in reproducing all the experimental XANES features are discussed.Comment: 15 pages, 5 figure

A model of driven and decaying magnetic turbulence in a cylinder

Using mean-field theory, we compute the evolution of the magnetic field in a cylinder with outer perfectly conducting boundaries, an imposed axial magnetic and electric field. The thus injected magnetic helicity in the system can be redistributed by magnetic helicity fluxes down the gradient of the local current helicity of the small-scale magnetic field. A weak reversal of the axial magnetic field is found to be a consequence of the magnetic helicity flux in the system. Such fluxes are known to alleviate so-called catastrophic quenching of the {\alpha}-effect in astrophysical applications. Application to the reversed field pinch in plasma confinement devices is discussed.Comment: 7 pages, 4 figures, submitted to Phys. Rev.

Optimized bone sampling protocols for the retrieval of ancient DNA from archaeological remains

The methods presented here seek to maximize the chances for the recovery of human DNA from ancient archaeological remains while limiting input sample material. This was done by targeting anatomical sampling locations previously determined to yield the highest amounts of ancient DNA (aDNA) in a comparative analysis of DNA recovery across the skeleton. Prior research has suggested that these protocols maximize the chances for the successful recovery of ancient human and pathogen DNA from archaeological remains. DNA yields were previously assessed by Parker et al. 2020 in a broad survey of aDNA preservation across multiple skeletal elements from 11 individuals recovered from the medieval (radiocarbon dated to a period of circa (ca.) 1040-1400 CE, calibrated 2-sigma range) graveyard at Krakauer Berg, an abandoned medieval settlement near Peißen Germany. These eight sampling spots, which span five skeletal elements (pars petrosa, permanent molars, thoracic vertebra, distal phalanx, and talus) successfully yielded high-quality ancient human DNA, where yields were significantly greater than the overall average across all elements and individuals. Yields were adequate for use in most common downstream population genetic analyses. Our results support the preferential use of these anatomical sampling locations for most studies involving the analyses of ancient human DNA from archaeological remains. Implementation of these methods will help to minimize the destruction of precious archaeological specimens.Introduction Protocol 1. Considerations before sample processing 2. Pretreatment 3. Bone powder generation Representative Results Discussio