72,055 research outputs found
MHD Interaction of Pulsar Wind Nebulae with SNRs and the ISM
In the late 1960s the discovery of the Crab pulsar in its associated
supernova remnant, launched a new field in supernova remnant research: the
study of pulsar-driven or plerionic supernova remnants. In these type of
remnants, the relativistic wind emitted by the pulsar, blows a pulsar wind
nebula into the interior of its supernova remnant. Now, more then forty years
after the discovery of the Crab pulsar, there are more then fifty plerionic
supernova remnants known, due to the ever-increasing capacity of observational
facilities. I will review our current understanding of the different
evolutionary stages of a pulsar wind nebula as it is interacting with its
associated supernova remnant.Therefore I will discuss both analytical and more
recent numerical (M)HD models.The four main stages of a pulsar wind nebula are:
the supersonic expansion stage, the reverse shock interaction stage, the
subsonic expansion stage and ultimatelythe stage when the head of the bubble is
bounded by a bow shock, due to the supersonic motion of the pulsar. Ultimately
this pulsar wind nebula bow shock will break through its associated remnant,
after which the pulsar-powered bow shock will interact directly with the
interstellar medium. I will discuss recent numerical models from these type of
pulsar wind nebulae and their morphology.Comment: 11 pages, 3 figures, Advances in Space Research, in pres
Why the distance of PSR J0218+4232 does not challenge pulsar emission theories
Recent VLBI measurements of the astrometric parameters of the millisecond
pulsar J0218+4232 by Du et al. have suggested this pulsar is as distant as 6.3
kpc. At such a large distance, the large {\gamma}-ray flux observed from this
pulsar would make it the most luminous {\gamma}-ray pulsar known. This
luminosity would exceed what can be explained by the outer gap and slot-gap
pulsar emission models, potentially placing important and otherwise elusive
constraints on the pulsar emission mechanism. We show that the VLBI parallax
measurement is dominated by the Lutz-Kelker bias. When this bias is corrected
for, the most likely distance for this pulsar is 3.15(+0.85/-0.60) kpc. This
revised distance places the luminosity of PSR J0218+4232 into a range where it
does not challenge any of the standard theories of the pulsar emission
mechanism.Comment: 3 pages, 2 figures, 1 table. Accepted for publication in MNRA
Bow-shock Pulsar Wind Nebulae Passing Through Density Discontinuities
Bow-shock pulsar wind nebulae are a subset of pulsar wind nebulae that form
when the pulsar has high velocity due to the natal kick during the supernova
explosion. The interaction between the relativistic wind from the fast-moving
pulsar and the interstellar medium produces a bow-shock and a trail, which are
detectable in H emission. Among such bow-shock pulsar wind nebulae,
the Guitar Nebula stands out for its peculiar morphology, which consists of a
prominent bow-shock head and a series of bubbles further behind. We present a
scenario in which multiple bubbles can be produced when the pulsar encounters a
series of density discontinuities in the ISM. We tested the scenario using 2-D
and 3-D hydrodynamic simulations. The shape of the guitar nebula can be
reproduced if the pulsar traversed a region of declining low density. We also
show that if a pulsar encounters an inclined density discontinuity, it produces
an asymmetric bow-shock head, consistent with observations of the bow-shock of
the millisecond pulsar J2124-3358.Comment: 12 pages, 11 figures, accepted for publication in MNRA
Hydrodynamic Interaction between the Be Star and the Pulsar in the TeV Binary PSR B1259-63/LS 2883
We study the interaction between the Be star and the pulsar in the TeV binary
PSR B1259-63/LS 2883, using 3-D SPH simulations of the tidal and wind
interactions in this Be-pulsar system. We first run a simulation without pulsar
wind nor Be wind, taking into account only the gravitational effect of the
pulsar on the Be disk. In this simulation, the gas particles are ejected at a
constant rate from the equatorial surface of the Be star, which is tilted in a
direction consistent with multi-waveband observations. We run the simulation
until the Be disk is fully developed and starts to repeat a regular tidal
interaction with the pulsar. Then, we turn on the pulsar wind and the Be wind.
We run two simulations with different wind mass-loss rates for the Be star, one
for a B2V type and the other for a significantly earlier spectral type.
Although the global shape of the interaction surface between the pulsar wind
and the Be wind agrees with the analytical solution, the effect of the pulsar
wind on the Be disk is profound. The pulsar wind strips off an outer part of
the Be disk, truncating the disk at a radius significantly smaller than the
pulsar orbit. Our results, therefore, rule out the idea that the pulsar passes
through the Be disk around periastron, which has been assumed in the previous
studies. It also turns out that the location of the contact discontinuity can
be significantly different between phases when the pulsar wind directly hits
the Be disk and those when the pulsar wind collides with the Be wind. It is
thus important to adequately take into account the circumstellar environment of
the Be star, in order to construct a satisfactory model for this prototypical
TeV binary.Comment: 10 pages, 5 figures, accepted for publication in PAS
Selection of radio pulsar candidates using artificial neural networks
Radio pulsar surveys are producing many more pulsar candidates than can be
inspected by human experts in a practical length of time. Here we present a
technique to automatically identify credible pulsar candidates from pulsar
surveys using an artificial neural network. The technique has been applied to
candidates from a recent re-analysis of the Parkes multi-beam pulsar survey
resulting in the discovery of a previously unidentified pulsar.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society. 9 pages, 7 figures, and 1 tabl
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