98 research outputs found

    Shocks, Outflows and Bubbles: New Views on Pulsars and their Winds

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    A typical young pulsar slows down at an imperceptible rate, its spin period increasing by less than 10 microseconds over the course of a year. However, the inertia of a pulsar is so extreme that to effect this tiny change in rotation rate, the star must dissipate about 10^46 ergs of kinetic energy. Observations of pulsars and their surroundings demonstrate that this ``spin-down energy'' is expelled into the pulsar's surroundings in spectacular fashion, in the form of a relativistic wind of charged particles and magnetic fields. In this review I highlight some recent observational results on pulsar winds at radio, X-ray and optical wavelengths, and explain what we can learn from these data about shock structure, particle acceleration and the interstellar medium.Comment: 8 pages, 4 embedded EPS figures, uses ws-procs9x6.cls. To appear in proceddings of "Texas in Tuscany" (XXI Symposium on Relativistic Astrophysics

    Cosmic Magnetism with the Square Kilometre Array and its Pathfinders

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    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"

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    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

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    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 21.76×21.7621.76\times 21.76 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 beam1^{-1} (average beam size of 2.6 arcmin), corresponding to 0.01-0.30 mJy arcmin2^{-2}. 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 μ\muG, depending heavily on the spectral index. We conclude that for a 3σ\sigma detection of 0.1 μ\muG magnetic field strengths via cross correlations, image depths of sub-mJy to sub-μ\muJy 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

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    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