2,491 research outputs found
Shocks, Outflows and Bubbles: New Views on Pulsars and their Winds
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
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
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
Radio continuum and polarization study of SNR G57.2+0.8 associated with magnetar SGR1935+2154
We present a radio continuum and linear polarization study of the Galactic
supernova remnant G57.2+0.8, which may host the recently discovered magnetar
SGR1935+2154. The radio SNR shows the typical radio continuum spectrum of a
mature supernova remnant with a spectral index of and
moderate polarized intensity. Magnetic field vectors indicate a tangential
magnetic field, expected for an evolved SNR, in one part of the SNR and a
radial magnetic field in the other. The latter can be explained by an
overlapping arc-like feature, perhaps a pulsar wind nebula, emanating from the
magnetar. The presence of a pulsar wind nebula is supported by the low average
braking index of 1.2, we extrapolated for the magnetar, and the detection of
diffuse X-ray emission around it. We found a distance of 12.5 kpc for the SNR,
which identifies G57.2+0.8 as a resident of the Outer spiral arm of the Milky
Way. The SNR has a radius of about 20 pc and could be as old as 41,000 years.
The SNR has already entered the radiative or pressure-driven snowplow phase of
its evolution. We compared independently determined characteristics like age
and distance for both, the SNR and SGR1935+2154, and conclude that they are
physically related.Comment: accepted by The Astrophysical Journal, 16 pages, 10 figure
A deep search for pulsar wind nebulae using pulsar gating
Using the Australia Telescope Compact Array (ATCA) we have imaged the fields
around five promising pulsar candidates to search for radio pulsar wind nebulae
(PWNe). We have used the ATCA in its pulsar gating mode; this enables an image
to be formed containing only off-pulse visibilities, thereby dramatically
improving the sensitivity to any underlying PWN. Data from the Molonglo
Observatory Synthesis Telescope were also used to provide sensitivity on larger
spatial scales. This survey found a faint new PWN around PSR B0906-49; here we
report on non-detections of PWNe towards PSRs B1046-58, B1055-52, B1610-50 and
J1105-6107. Our radio observations of the field around PSR B1055-52 argue
against previous claims of an extended X-ray and radio PWNe associated with the
pulsar. If these pulsars power unseen, compact radio PWN, upper limits on the
radio flux indicate that less than 1e-6 of their spin-down energy is used to
power this emission. Alternatively PSR B1046-58 and PSR B1610-50 may have
relativistic winds similar to other young pulsars and the unseen PWN is
resolved and fainter than our surface brightness sensitivity threshold. We can
then determine upper limits on the local ISM density of 2.2e-3 cm^-3 and 1e-2
cm^-3, respectively. Furthermore we constrain the spatial velocities of these
pulsars to be less than ~450 km/s and thus rule out the association of PSR
B1610-50 with SNR G332.4+00.1 (Kes 32). Strong limits on the ratio of unpulsed
to pulsed emission are also determined for three pulsars.Comment: 10 pages, 5 figures, MNRAS in pres
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