252 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
Nonthermal X-ray emission from young Supernova Remnants
The cosmic-ray spectrum up to the knee ( eV) is attributed to
acceleration processes taking place at the blastwaves which bound supernova
remnants. Theoretical predictions give a similar estimate for the maximum
energy which can be reached at supernova remnant shocks by particle
acceleration. Electrons with energies of the order eV should
give a nonthermal X-ray component in young supernova remnants. Recent
observations of SN1006 and G347.3-0.5 confirm this prediction. We present a
method which uses hydrodynamical simulations to describe the evolution of a
young remnant. These results are combined with an algorithm which
simultaneously calculates the associated particle acceleration. We use the test
particle approximation, which means that the back-reaction on the dynamics of
the remnant by the energetic particles is neglected. We present synchrotron
maps in the X-ray domain, and present spectra of the energies of the electrons
in the supernova remnant. Some of our results can be compared directly with
earlier semi-analytical work on this subject by Reynolds [1].Comment: 4 pages, 2 figures, contribution proceedings of poster presented at
the 11th Annual Astrophysics Conference in Maryland, to appear in Young
Supernova Remnants, ed. by S. S. Holt and U. Hwang (AIP
Pulsar wind nebulae in supernova remnants
A spherically symmetric model is presented for the interaction of a pulsar
wind with the associated supernova remnant. This results in a pulsar wind
nebula whose evolution is coupled to the evolution of the surrounding supernova
remnant. This evolution can be divided in three stages. The first stage is
characterised by a supersonic expansion of the pulsar wind nebula into the
freely expanding ejecta of the progenitor star. In the next stage the pulsar
wind nebula is not steady; the pulsar wind nebula oscillates between
contraction and expansion due to interaction with the reverse shock of the
supernova remnant: reverberations which propagate forward and backward in the
remnant. After the reverberations of the reverse shock have almost completely
vanished and the supernova remnant has relaxed to a Sedov solution, the
expansion of the pulsar wind nebula proceeds subsonically. In this paper we
present results from hydrodynamical simulations of a pulsar wind nebula through
all these stages in its evolution. The simulations were carried out with the
Versatile Advection Code.Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysic
Interaction of a magnetized pulsar wind with its surroundings. MHD simulations of Pulsar Wind Nebulae
Magnetohydrodynamical simulations are presented of a magnetized pulsar wind
interacting directly with the interstellar medium, or, in the case of a
surrounding supernova remnant, with the associated freely expanding ejecta of
the progenitor star. In both cases the simulations show that the pulsar wind
nebula will be elongated due to the dynamical influence of the toroidal
magnetic fields, which confirm predictions from a semi-analytical model
presented by Begelman & Li. The simulations follow the expansion of the pulsar
wind nebula when the latter is bounded by a strong shock and show that the
expansion can be modeled with a standard power-law expansion rate. By
performing different simulations with different magnetization parameters, I
show that the latter weakly correlates with the elongation of the pulsar wind
nebula. The results from the simulations are applied to determine the nature of
the expansion rate of the pulsar wind nebula 3C58. It is shown that there is
both observational and theoretical evidence which supports the scenario in
which the pulsar wind nebula 3C58 has caught up with the reverse shock of the
associated (but undetected) supernova remnant.Comment: 9 pages, 8 figures, accepted for A&
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