Probing QCD approach to thermal equilibrium with ultrahigh energy cosmic rays

The Pierre Auger Collaboration has reported an excess in the number of muons of a few tens of percent over expectations computed using extrapolation of hadronic interaction models tuned to accommodate LHC data. Very recently, we proposed an explanation for the muon excess assuming the formation of a deconfined quark matter (fireball) state in central collisions of ultrarelativistic cosmic rays with air nuclei. At the first stage of its evolution the fireball contains gluons as well as $u$ and $d$ quarks. The very high baryochemical potential inhibits gluons from fragmenting into $u \bar u$ and $d \bar d$, and so they fragment predominantly into $s \bar s$ pairs. In the hadronization which follows this leads to the strong suppression of pions and hence photons, but allows heavy hadrons to be emitted carrying away strangeness. In this manner, the extreme imbalance of hadron to photon content provides a way to enhance the muon content of the air shower. In this communication we study theoretical systematics from hadronic interaction models used to describe the cascades of secondary particles produced in the fireball explosion. We study the predictions of one of the leading LHC-tuned models QGSJET II-04 considered in the Auger analysis.Comment: 7 pages LaTeX, 6 .pdf figure

Circumstellar Interaction Around Type Ib/c Supernovae and the GRB Connection

Radio observations of Type Ib/c supernovae suggest that circumstellar interaction takes place with a wide range of wind densities, comparable to that seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in the shocked region is needed. The X-ray emission observed from some Type Ib/c supernovae is higher than would be expected by the thermal or inverse Compton mechanisms; a synchrotron interpretation requires a flattening of the electron energy spectrum at high energies, as might occur in a cosmic ray dominated shock wave. The wind density variations that are indicated in two supernovae may be due to a binary companion, although variable mass loss from a single star remains a possibility. Other than the optical supernova radiation, the emission from the nearby SN 2006aj/GRB 060218 appears to be powered by a central engine, while that from SN 1998bw/GRB 980425 could be powered by either a central engine or the outer supernova ejecta.Comment: 8 pages, to appear in Circumstellar Media and Late Stages of Massive Stellar Evolution, RevMexA

Magneto-optical imaging of voltage-controlled magnetization reorientation

We study the validity and limitations of a macrospin model to describe the voltage-controlled manipulation of ferromagnetic magnetization in nickel thin film/piezoelectric actuator hybrid structures. To this end, we correlate simultaneously measured spatially resolved magneto-optical Kerr effect imaging and integral magnetotransport measurements at room temperature. Our results show that a macrospin approach is adequate to model the magnetoresistance as a function of the voltage applied to the hybrid, except for a narrow region around the coercive field - where the magnetization reorientation evolves via domain effects. Thus, on length scales much larger than the typical magnetic domain size, the voltage control of magnetization is well reproduced by a simple Stoner-Wohlfarth type macrospin model

Radiative damping in wave guide based FMR measured via analysis of perpendicular standing spin waves in sputtered Permalloy films

The damping $\alpha$ of the spinwave resonances in 75 nm, 120 nm, and 200nm -thick Permalloy films is measured via vector-network-analyzer ferromagnetic-resonance (VNA-FMR) in the out-of-plane geometry. Inductive coupling between the sample and the waveguide leads to an additional radiative damping term. The radiative contribution to the over-all damping is determined by measuring perpendicular standing spin waves (PSSWs) in the Permalloy films, and the results are compared to a simple analytical model. The damping of the PSSWs can be fully explained by three contributions to the damping: The intrinsic damping, the eddy-current damping, and the radiative damping. No other contributions were observed. Furthermore, a method to determine the radiative damping in FMR measurements with a single resonance is suggested

Radio Spectral Index and Expansion of 3C58

We present new observations of the plerionic supernova remnant 3C58 with the VLA at 74 and 327 MHz. In addition, we re-reduced earlier observations at 1.4 and 4.9 GHz taken in 1973 and 1984. Comparing these various images, we find that: 1. the remnant has a flat and relatively uniform spectral index distribution, 2. any expansion of the remnant with time is significantly less than that expected for uniform, undecelerated expansion since the generally accepted explosion date in 1181 A.D., and 3. there is no evidence for a non-thermal synchrotron emission shell generated by a supernova shock wave, with any such emission having a surface brightness of <1 x 10^(-21) W / (m^2 Hz sr) at 327 MHz.Comment: 18 pages, 7 Figures, Latex, Accepted for publication in the Astrophysical Journa