An Auger test of the Cen A model of highest energy cosmic rays

If, as recently proposed by Farrar and Piran, Cen A is the source of cosmic rays detected above the Greisen-Zatsepin-Kuz'min cutoff, neutrons are $\approx 700$ more probable than protons to be observed along its line of sight. This is because the proton flux is rendered nearly isotropic by ${\cal O}(\mu$G) intergalactic magnetic fields. With the anticipated aperture of the Southern Auger Observatory, one may expect on the order of 10 neutron events/year above $10^{20}$ eV in the line of sight of Cen A

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

End of the cosmic neutrino energy spectrum

There may be a high-energy cutoff of neutrino events in IceCube data. In particular, IceCube does not observe either continuum events above 2 PeV, or the Standard Model Glashow-resonance events expected at 6.3 PeV. There are also no higher energy neutrino signatures in the ANITA and Auger experiments. This absence of high-energy neutrino events motivates a fundamental restriction on neutrino energies above a few PeV. We postulate a simple scenario to terminate the neutrino spectrum that is Lorentz-invariance violating, but with a limiting neutrino velocity that is always smaller than the speed of light. If the limiting velocity of the neutrino applies also to its associated charged lepton, then a significant consequence is that the two-body decay modes of the charged pion are forbidden above two times the maximum neutrino energy, while the radiative decay modes are suppressed at higher energies. Such stabilized pions may serve as cosmic ray primaries.Comment: 6 pages. Version to appear in PL

The X-ray Spectrum and Light Curve of Supernova 1995N

We report on multi-epoch X-ray observations of the Type IIn (narrow emission line) supernova SN 1995N with the ROSAT and ASCA satellites. The January 1998 ASCA X-ray spectrum is well fitted by a thermal bremsstrahlung (kT~10 keV, N_H~6e20 cm^-2) or power-law (alpha~1.7, N_H~1e21 cm^-2) model. The X-ray light curve shows evidence for significant flux evolution between August 1996 and January 1998: the count rate from the source decreased by 30% between our August 1996 and August 1997 ROSAT observations, and the X-ray luminosity most likely increased by a factor of ~2 between our August 1997 ROSAT and January 1998 ASCA observations, although evolution of the spectral shape over this interval is not ruled out. The high X-ray luminosity, L_X~1e41 erg/sec, places SN 1995N in a small group of Type IIn supernovae with strong circumstellar interaction, and the evolving X-ray luminosity suggests that the circumstellar medium is distributed inhomogeneously.Comment: MNRAS accepted. 6 pages, 2 figures; uses mn.sty and psfi

OH Zeeman Magnetic Field Detections Toward Five Supernova Remnants Using the VLA

We have observed the OH (1720 MHz) line in five galactic SNRs with the VLA to measure their magnetic field strengths using the Zeeman effect. We detected all 12 of the bright ($S_{\nu} > 200$ mJy) OH (1720 MHz) masers previously detected by Frail et al. (1996) and Green et al. (1997) and measured significant magnetic fields (i.e. $> 3\sigma$) in ten of them. Assuming that the ``thermal'' Zeeman equation can be used to estimate $\mid\vec{B}\mid$ for OH masers, our estimated fields range from 0.2 to 2 mG. These magnetic field strengths are consistent with the hypothesis that ambient molecular cloud magnetic fields are compressed via the SNR shock to the observed values. Magnetic fields of this magnitude exert a considerable influence on the properties of the cloud with the magnetic pressures ($10^{-7} - 10^{-9}$ erg cm$^{-3}$) exceeding the pressure in the ISM or even the thermal pressure of the hot gas interior to the remnant. This study brings the number of galactic SNRs with OH (1720 MHz) Zeeman detections to ten.Comment: 23 pages, 14 figures, accepted to ApJ, for higher resolution images of Figs 4,11, and 12 see http://www.pa.uky.edu/~brogan/brog_publ.htm

Magnetic interference patterns in 0-Pi SIFS Josephson junctions: effects of asymmetry between 0 and Pi regions

We present a detailed analysis of the dependence of the critical current I_c on the magnetic field B of 0, Pi, and 0-Pi superconductor-insulator-ferromagnet-superconductor Josephson junctions. I_c(B) of the 0 and Pi junction closely follows a Fraunhofer pattern, indicating a homogeneous critical current density j_c(x). The maximum of I_c(B) is slightly shifted along the field axis, pointing to a small remanent in-plane magnetization of the F-layer along the field axis. I_c(B) of the 0-Pi junction exhibits the characteristic central minimum. I_c however has a finite value here, due to an asymmetry of j_c in the 0 and Pi part. In addition, this I_c(B) exhibits asymmetric maxima and bumped minima. To explain these features in detail, flux penetration being different in the 0 part and the Pi part needs to be taken into account. We discuss this asymmetry in relation to the magnetic properties of the F-layer and the fabrication technique used to produce the 0-Pi junctions

G328.4+0.2 : A large and luminous Crab-like supernova remnant

We report on radio continuum and HI observations of the radio source G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing significant linear polarization and an almost flat spectral index. These results lead us to conclude that G328.4+0.2 is a Crab-like, or ``plerionic'', supernova remnant (SNR), presumably powered by an unseen central pulsar. HI absorption towards G328.4+0.2 puts a lower limit on its distance of 17.4 +/- 0.9 kpc, making it the largest (D=25 pc) and most luminous (L_R = 3e35 erg/s) Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than the Crab Nebula, but powered by a pulsar which is fast spinning (P<20 ms) and which has a comparatively low magnetic field (B<1e12 G). We propose G328.4+0.2, G74.9+1.2 and N157B as a distinct group of large-diameter, high-luminosity Crab-like SNRs, all powered by fast-spinning low-field pulsars.Comment: 7 pages, 3 embedded EPS figures, uses emulateapj.sty. Accepted to ApJ. Abstract corrected so that distance is now in kpc, not pc