86 research outputs found
Cosmic Magnetism with the Square Kilometre Array and its Pathfinders
One of the five key science projects for the Square Kilometre Array (SKA) is
"The Origin and Evolution of Cosmic Magnetism", in which radio polarimetry will
be used to reveal what cosmic magnets look like and what role they have played
in the evolving Universe. Many of the SKA prototypes now being built are also
targeting magnetic fields and polarimetry as key science areas. Here I review
the prospects for innovative new polarimetry and Faraday rotation experiments
with forthcoming facilities such as ASKAP, LOFAR, the ATA, the EVLA, and
ultimately the SKA. Sensitive wide-field polarisation surveys with these
telescopes will provide a dramatic new view of magnetic fields in the Milky
Way, in nearby galaxies and clusters, and in the high-redshift Universe.Comment: 7 pages, including 2 colour figures. To appear in proceedings of IAU
Symposium 259: "Cosmic Magnetic Fields: From Planets, To Stars and Galaxies",
Tenerife, Nov 200
"A Search For The Young and Energetic Pulsar in G328.4+0.2"
The pulsar-powered nebula G328.4+0.2 is one of the largest and most luminous such sources known. The nature of G328.4+0.2 has been a source of controversy - the object s flat radio spectral index has been used to argue that this object is a young pulsar wind nebula (PWN), while others have used radial protrusions in the magnetic field orientation along the source s outer edge to argue that it is an old supernova remnant (SNR). In the first interpretation, the X-ray nebula inside this radio source would be located inside the central "bar" detected in the radio. In the second interpretation, the expectation is that the X-ray PWN would be located at either end of this central "bar". The goals of our XMM observation were to try and detect the pulsar, and to use its location and other properties to distinguish between the above two possibilities
Low Frequency Radio Constraints on the Synchrotron Cosmic Web
We present a search for the synchrotron emission from the synchrotron cosmic
web by cross correlating 180MHz radio images from the Murchison Widefield Array
with tracers of large scale structure (LSS). We use two versions of the radio
image covering degrees with point sources brighter than
0.05 Jy subtracted, with and without filtering of Galactic emission. As tracers
of the LSS we use the Two-Micron-All-Sky-Survey (2MASS) and the Widefield
InfraRed Explorer (WISE) redshift catalogues to produce galaxy number density
maps. The cross correlation functions all show peak amplitudes at zero degrees,
decreasing with varying slopes towards zero correlation over a range of one
degree. The cross correlation signals include components from point source,
Galactic, and extragalactic diffuse emission. We use models of the diffuse
emission from smoothing the density maps with Gaussians of sizes 1-4 Mpc to
find limits on the cosmic web components. From these models we find surface
brightness 99.7 per cent upper limits in the range of 0.09-2.20 mJy beam
(average beam size of 2.6 arcmin), corresponding to 0.01-0.30 mJy
arcmin. Assuming equipartition between energy densities of cosmic rays
and the magnetic field, the flux density limits translate to magnetic field
strength limits of 0.03-1.98 G, depending heavily on the spectral index.
We conclude that for a 3 detection of 0.1 G magnetic field
strengths via cross correlations, image depths of sub-mJy to sub-Jy are
necessary. We include discussion on the treatment and effect of extragalactic
point sources and Galactic emission, and next steps for building on this work.Comment: 25 pages, 18 figures, 4 tables, accepted for publication in MNRA
Bow shocks around pulsars and neutron stars
Pulsar wind nebulae are now well established as important probes both of
neutron stars' relativistic winds and of the surrounding interstellar medium.
Amongst this diverse group of objects, pulsar bow shocks have long been
regarded as an oddity, only seen around a handful of rapidly moving neutron
stars. However, recent efforts at optical, radio and X-ray wavelengths have
identified many new pulsar bow shocks, and these results have consequently
motivated renewed theoretical efforts to model these systems. Here I review the
new results and ideas which have emerged on these spectacular systems, and
explain how bow shocks and "Crab-like" nebulae now form a consistent picture
within our understanding of pulsar winds.Comment: 12 pages, 2 embedded EPS figures, 1 GIF figure. Advances in Space
Research, in pres
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