6,017 research outputs found
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
Radio Detection of SN 1986E in NGC 4302
Radio observations of SN 1986E have shown a clear detection of emission at 6
cm wavelength about 8 months after optical discovery. Combined with a number of
new upper limits and a study of the possible models, it appears that SN 1986E
was probably a fairly normal Type IIL supernova, somewhat similar to SN 1980K,
with radio emission at roughly expected levels. This detection continues the
correlation between radio detection and late time optical emission.Comment: 14 pages, LaTeX (AASTeX), 2 PostScript figures, to appear in ApJ
(Letters
High Energy Cosmic Rays from Neutrinos
We discuss recent models in which neutrinos, which are assumed to have mass
in the eV range, originate the highest energy cosmic rays by interaction with
the enhanced density in the galactic halo of the relic cosmic neutrino
background. We make an analytical calculation of the required neutrino fluxes
to show that the parameter space for these models is constrained by horizontal
air shower searches and by the total number of background neutrinos, so that
only models which have fairly unnatural halo sizes and enhanced densities are
allowed.Comment: 14 pages, 3 ps figures. To appear in Phys. Rev.
Double fermiophobic Higgs boson production at the LHC and LC
We consider the phenomenology of a fermiophobic Higgs boson (h_f) at the
Large Hadron Collider (LHC) and a e+e- Linear Collider (LC). At both machines
the standard production mechanisms which rely on the coupling h_fVV (V=W,Z) can
be very suppressed at large tan beta. In such cases the complementary channels
pp to H^\pm h_f, A^0 h_f and e+e- to A^0 h_f offer promising cross-sections.
Together with the potentially large branching ratios for H^\pm to h_fW* and A^0
to h_fZ*, these mechanisms would give rise to double h_f production, leading to
signatures of gamma gamma gamma gamma, gamma gamma VV and VVVV.Comment: 19 pages, 9 figures, expanded discussion, fig.1 changed slightly,
version to appear in Phys.Rev.
Form and function in hillslope hydrology : Characterization of subsurface ow based on response observations
Acknowledgements. We are grateful to Marcel Delock, Lisei Köhn, and Marvin Reich for their support during fieldwork, as well as Markus Morgner and Jean Francois Iffly for technical support, Britta Kattenstroth for hydrometeorological data acquisition and isotope sampling, and Barbara Herbstritt and Begoña Lorente Sistiaga for laboratory work. Laurent Pfister and Jean-Francois Iffly from the Luxembourg Institute of Science and Technology (LIST) are acknowledged for organizing the permissions for the experiments and providing discharge data for Weierbach 1 and Colpach. We also want to thank Frauke K. Barthold and the two anonymous reviewers, whose thorough remarks greatly helped to improve the manuscript. This study is part of DFG-funded CAOS project âFrom Catchments as Organised Systems to Models based on Dynamic Functional Unitsâ (FOR 1598). The article processing charges for this open-access publication were covered by a Research Centre of the Helmholtz Association.Peer reviewedPublisher PD
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
Decay of High-Energy Astrophysical Neutrinos
Existing limits on the non-radiative decay of one neutrino to another plus a
massless particle (e.g., a singlet Majoron) are very weak. The best limits on
the lifetime to mass ratio come from solar neutrino observations, and are
\tau/m \agt 10^{-4} s/eV for the relevant mass eigenstate(s). For lifetimes
even several orders of magnitude longer, high-energy neutrinos from distant
astrophysical sources would decay. This would strongly alter the flavor ratios
from the expected
from oscillations alone, and should be readily visible in the near future in
detectors such as IceCube.Comment: 4 pages, 1 figure. References added. Version to appear in PR
Resonant conversions of extremely high energy neutrinos in dark matter halos
We study the effect of adiabatically resonant conversion in galactic halos of
neutrinos at the highest energies ( - eV), when the
source is in the center of a galaxy. Using the standard neutrino
properties and the standard cosmological scenario for the hot dark part of
matter, we find that interesting conversions may take place just for neutrino
parameters relevant to the solar and atmospheric neutrino problem. The effect
is due to the large enhancement in the density in galactic halos and to
the form of the effective matter potential both below and above the pole of the
resonance.Comment: 8 pages, revtex, some comments and references added, to appear in
Phys. Rev.
The LWA1 Radio Telescope
LWA1 is a new radio telescope operating in the frequency range 10-88 MHz,
located in central New Mexico. The telescope consists of 258 pairs of
dipole-type antennas whose outputs are individually digitized and formed into
beams. Simultaneously, signals from all dipoles can be recorded using one of
the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable
features of the instrument include high intrinsic sensitivity (about 6 kJy
zenith system equivalent flux density), large instantaneous bandwidth (up to 78
MHz), and 4 independently-steerable beams utilizing digital "true time delay"
beamforming. This paper summarizes the design of LWA1 and its performance as
determined in commissioning experiments. We describe the method currently in
use for array calibration, and report on measurements of sensitivity and
beamwidth.Comment: 9 pages, 14 figures, accepted by IEEE Trans. Antennas & Propagation.
Various minor changes from previous versio
Swift UVOT Observations of Core-Collapse SNe
We review recent UV observations of core-collapse supernovae (SNe) with the
Swift Ultra-violet/Optical Telescope (UVOT) during its first two years.
Rest-frame UV photometry is useful for differentiating SN types by exploiting
the UV-optical spectral shape and more subtle UV features. This is useful for
the real-time classification of local and high-redshift SNe using only
photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a
UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after
the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV
observations are also useful for constraining the temperature and ionization
structure of SNe IIP. Rest-frame UV observations of all types are important for
understanding the extinction, temperature, and bolometric luminosity of SNe and
to interpret the observations of high redshift SNe observed at optical
wavelengths.Comment: Figures are enlarged and colorized from print versio
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