Spontaneous Transport Barriers Quench Turbulent Resistivity in 2D MHD

This Letter identifies the physical mechanism for the quench of turbulent resistivity in 2D MHD. Without an imposed, ordered magnetic field, a multi-scale, blob-and-barrier structure of magnetic potential forms spontaneously. Magnetic energy is concentrated in thin, linear barriers, located at the interstices between blobs. The barriers quench the transport and kinematic decay of magnetic energy. The local transport bifurcation underlying barrier formation is linked to the inverse cascade of $\langle A^2\rangle$ and negative resistivity, which induce local bistability. For small scale forcing, spontaneous layering of the magnetic potential occurs, with barriers located at the interstices between layers. This structure is effectively a magnetic staircase

Fluid Models for Kinetic Effects on Coherent Nonlinear Alfven Waves. II. Numerical Solutions

The influence of various kinetic effects (e.g. Landau damping, diffusive and collisional dissipation, and finite Larmor radius terms) on the nonlinear evolution of finite amplitude Alfvenic wave trains in a finite-beta environment is systematically investigated using a novel, kinetic nonlinear Schrodinger (KNLS) equation. The dynamics of Alfven waves is sensitive to the sense of polarization as well as the angle of propagation with respect to the ambient magnetic field. Numerical solution for the case with Landau damping reveals the formation of dissipative structures, which are quasi-stationary, S-polarized directional (and rotational) discontinuities which self-organize from parallel propagating, linearly polarized waves. Parallel propagating circularly polarized packets evolve to a few circularly polarized Alfven harmonics on large scales. Stationary arc-polarized rotational discontinuities form from obliquely propagating waves. Collisional dissipation, even if weak, introduces enhanced wave damping when beta is very close to unity. Cyclotron motion effects on resonant particle interactions introduce cyclotron resonance into the nonlinear Alfven wave dynamics.Comment: 38 pages (including 23 figures and 1 table

Galaxies Probing Galaxies in PRIMUS - I. Sample, Spectroscopy, and Characteristics of the z~0.5 MgII-Absorbing Circumgalactic Medium

Spectroscopy of background QSO sightlines passing close to foreground galaxies is a potent technique for studying the circumgalactic medium (CGM). QSOs are effectively point sources, however, limiting their potential to constrain the size of circumgalactic gaseous structures. Here we present the first large Keck/LRIS and VLT/FORS2 spectroscopic survey of bright (B_AB < 22.3) background galaxies whose lines of sight probe MgII 2796, 2803 absorption from the CGM around close projected foreground galaxies at transverse distances 10 kpc < R_perp < 150 kpc. Our sample of 72 projected pairs, drawn from the PRIsm MUlti-object Survey (PRIMUS), includes 48 background galaxies which do not host bright AGN, and both star-forming and quiescent foreground galaxies with stellar masses 9.0 < log M_*/M_sun < 11.2 at redshifts 0.35 < z_f/g < 0.8. We detect MgII absorption associated with these foreground galaxies with equivalent widths 0.25 Ang 2sigma significance in 20 individual background sightlines passing within R_perp < 50 kpc, and place 2sigma upper limits on W_2796 of <0.5 Ang in an additional 11 close sightlines. Within R_perp < 50 kpc, W_2796 is anticorrelated with R_perp, consistent with analyses of MgII absorption detected along background QSO sightlines. Subsamples of these foreground hosts divided at log M_*/M_sun = 9.9 exhibit statistically inconsistent W_2796 distributions at 30 kpc < R_perp < 50 kpc, with the higher-M_* galaxies yielding a larger median W_2796 by 0.9 Ang. Finally, we demonstrate that foreground galaxies with similar stellar masses exhibit the same median W_2796 at a given R_perp to within <0.2 Ang toward both background galaxies and toward QSO sightlines drawn from the literature. Analysis of these datasets constraining the spatial coherence scale of circumgalactic MgII absorption is presented in a companion paper.Comment: 36 pages, 18 figures, 5 tables. Accepted to Ap

Unraveling the Infrared Transient VVV-WIT-06: The Case for the Origin as a Classical Nova

Indexación: Scopus.E.Y.H. acknowledges the support provided by the National Science Foundation under Grant No. AST-1613472 and by the Florida Space Grant Consortium. L.G. acknowledges support from the FINCA visitor programme. The research work at the Physical Research Laboratory is funded by the Department of Space, Government of India. Facility: Magellan: Baade(FIRE).The enigmatic near-infrared transient VVV-WIT-06 underwent a large-amplitude eruption of unclear origin in 2013 July. Based on its light curve properties and late-time post-outburst spectra, various possibilities have been proposed in the literature for the origin of the object, namely a Type I supernova, a classical nova (CN), or a violent stellar merger event. We show that, of these possibilities, an origin in a CN outburst convincingly explains the observed properties of VVV-WIT-06. We estimate that the absolute K-band magnitude of the nova at maximum was M k = -8.2 ±0.5, its distance d = 13.35 ±2.18 kpc, and the extinction A v = 15.0 ±0.55 mag. © 2018. The American Astronomical Society. All rights reserved.https://iopscience.iop.org/article/10.3847/1538-4357/aae5d

Electrocardiographic features suggestive of a left. ventricular' aneurysm following a high-velocity missile injury

Electrocardiographic features suggestive of a transmural anterior myocardial infarction with resultant left ventricular aneurysm formation were found in a 22-year-old man who had sustained a ballistic missile injury to his chest

Galaxies Probing Galaxies at High Resolution: Co-Rotating Gas Associated with a Milky Way Analog at z=0.4

We present results on gas flows in the halo of a Milky Way-like galaxy at z=0.413 based on high-resolution spectroscopy of a background galaxy. This is the first study of circumgalactic gas at high spectral resolution towards an extended background source (i.e., a galaxy rather than a quasar). Using longslit spectroscopy of the foreground galaxy, we observe spatially extended H alpha emission with circular rotation velocity v=270 km/s. Using echelle spectroscopy of the background galaxy, we detect Mg II and Fe II absorption lines at impact parameter rho=27 kpc that are blueshifted from systemic in the sense of the foreground galaxy's rotation. The strongest absorber EW(2796) = 0.90 A has an estimated column density (N_H>10^19 cm-2) and line-of-sight velocity dispersion (sigma=17 km/s) that are consistent with the observed properties of extended H I disks in the local universe. Our analysis of the rotation curve also suggests that this r=30 kpc gaseous disk is warped with respect to the stellar disk. In addition, we detect two weak Mg II absorbers in the halo with small velocity dispersions (sigma<10 km/s). While the exact geometry is unclear, one component is consistent with an extraplanar gas cloud near the disk-halo interface that is co-rotating with the disk, and the other is consistent with a tidal feature similar to the Magellanic Stream. We can place lower limits on the cloud sizes (l>0.4 kpc) for these absorbers given the extended nature of the background source. We discuss the implications of these results for models of the geometry and kinematics of gas in the circumgalactic medium.Comment: 14 pages, 6 figures, submitted to ApJ, comments welcom

Nonlinear shock acceleration beyond the Bohm limit

We suggest a physical mechanism whereby the acceleration time of cosmic rays by shock waves can be significantly reduced. This creates the possibility of particle acceleration beyond the knee energy at ~10^15eV. The acceleration results from a nonlinear modification of the flow ahead of the shock supported by particles already accelerated to the knee momentum at p ~ p_*. The particles gain energy by bouncing off converging magnetic irregularities frozen into the flow in the shock precursor and not so much by re-crossing the shock itself. The acceleration rate is thus determined by the gradient of the flow velocity and turns out to be formally independent of the particle mean free path (m.f.p.). The velocity gradient is, in turn, set by the knee-particles at p ~ p_* as having the dominant contribution to the CR pressure. Since it is independent of the m.f.p., the acceleration rate of particles above the knee does not decrease with energy, unlike in the linear acceleration regime. The reason for the knee formation at p ~ p_* is that particles with $p > p_*$ are effectively confined to the shock precursor only while they are within limited domains in the momentum space, while other particles fall into ``loss-islands'', similar to the ``loss-cone'' of magnetic traps. This structure of the momentum space is due to the character of the scattering magnetic irregularities. They are formed by a train of shock waves that naturally emerge from unstably growing and steepening magnetosonic waves or as a result of acoustic instability of the CR precursor. These losses steepen the spectrum above the knee, which also prevents the shock width from increasing with the maximum particle energy.Comment: aastex, 13 eps figure

Intrinsic properties of the magnetically collimated water maser jet of W43A

Water maser polarization observations in the precessing jet of W43A have revealed that it is magnetically collimated. Here we present a detailed description of the physical properties of the water maser environment in the jet. We discuss the maser saturation level and beaming angle as well as the intrinsic temperatures and densities. Additionally, we show that the polarization angle of the strongest red-shifted maser feature undergoes a fast rotation of 90 degrees across the maser. Along with the variation of linear polarization fraction, this strongly supports the current theoretical description of maser linear polarization.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter

Axial Symmetry and Rotation in the SiO Maser Shell of IK Tauri

We observed v=1, J=1-0 43-GHz SiO maser emission toward the Mira variable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 x 32 mas with an axial ratio of 1.8:1. The major axis of this elliptical distribution is oriented at position angle of ~59 deg. The line-of-sight velocity structure of the SiO masers has an apparent axis of symmetry consistent with the elongation axis of the maser distribution. Relative to the assumed stellar velocity of 35 km/s, the blue- and red-shifted masers were found to lie to the northwest and southeast of this symmetry axis respectively. This velocity structure suggests a NW-SE rotation of the SiO maser shell with an equatorial velocity, which we determine to be ~3.6 km/s. Such a NW-SE rotation is in agreement with a circumstellar envelope geometry invoked to explain previous water and OH maser observations. In this geometry, water and OH masers are preferentially created in a region of enhanced density along the NE-SW equator orthogonal to the rotation/polar axis suggested by the SiO maser velocities.Comment: 17 Pages, 4 figures (2 color); accepted for publication in Ap