162 research outputs found
The role of the Weibel instability at the reconnection jet front in relativistic pair plasma reconnection
The role of the Weibel instability is investigated for the first time in the
context of the large-scale magnetic reconnection problem. A late-time evolution
of magnetic reconnection in relativistic pair plasmas is demonstrated by
particle-in-cell (PIC) simulations. In the outflow regions, powerful
reconnection jet piles up the magnetic fields and then a tangential
discontinuity appears there. Further downstream, it is found that the
two-dimensional extension of the relativistic Weibel instability generates
electro-magnetic fields, which are comparable to the anti-parallel or piled-up
fields. In a microscopic viewpoint, the instability allows plasma's multiple
interactions with the discontinuity. In a macroscopic viewpoint, the
instability leads to rapid expansion of the current sheet and then the
reconnection jet front further propagates into the downstream. Possible
application to the three-dimensional case is briefly discussed.Comment: 25 pages, 9 figures; References and typos are fixe
Self-regulation of the reconnecting current layer in relativistic pair plasma reconnection
We investigate properties of the reconnecting current layer in relativistic
pair plasma reconnection. We found that the current layer self-regulates its
thickness when the current layer runs out current carriers, and so relativistic
reconnection retains a fast reconnection rate. Constructing a steady state
Sweet-Parker model, we discuss conditions for the current sheet expansion.
Based on the energy argument, we conclude that the incompressible assumption is
invalid in relativistic Sweet-Parker reconnection. The guide field cases are
more incompressible than the anti-parallel cases, and we find a more
significant current sheet expansion.Comment: Accepted for publication in Astrophysical Journal (to appear in vol.
685
Relativistic Particle Acceleration in a Folded Current Sheet
Two-dimensional particle simulations of a relativistic Harris current sheet
of pair plasmashave demonstrated that the system is unstable to the
relativistic drift kink instability (RDKI) and that a new kind of acceleration
process takes place in the deformed current sheet. This process contributes to
the generation of non-thermal particles and contributes to the fast magnetic
dissipation in the current sheet structure. The acceleration mechanism and a
brief comparison with relativistic magnetic reconnection are presented.Comment: 11 preprint pages, including 3 .eps figure
Covariant form of the ideal magnetohydrodynamic "connection theorem" in a relativistic plasma
The magnetic connection theorem of ideal Magnetohydrodynamics by Newcomb
[Newcomb W.A., Ann. Phys., 3, 347 (1958)] and its covariant formulation are
rederived and reinterpreted in terms of a "time resetting" projection that
accounts for the loss of simultaneity in different reference frames between
spatially separated events.Comment: 3 pages- 0 figures EPL, accepted in pres
Particle-in-cell simulations of shock-driven reconnection in relativistic striped winds
By means of two- and three-dimensional particle-in-cell simulations, we
investigate the process of driven magnetic reconnection at the termination
shock of relativistic striped flows. In pulsar winds and in magnetar-powered
relativistic jets, the flow consists of stripes of alternating magnetic field
polarity, separated by current sheets of hot plasma. At the wind termination
shock, the flow compresses and the alternating fields annihilate by driven
magnetic reconnection. Irrespective of the stripe wavelength "lambda" or the
wind magnetization "sigma" (in the regime sigma>>1 of magnetically-dominated
flows), shock-driven reconnection transfers all the magnetic energy of
alternating fields to the particles, whose average Lorentz factor increases by
a factor of sigma with respect to the pre-shock value. In the limit
lambda/(r_L*sigma)>>1, where r_L is the relativistic Larmor radius in the wind,
the post-shock particle spectrum approaches a flat power-law tail with slope
around -1.5, populated by particles accelerated by the reconnection electric
field. The presence of a current-aligned "guide" magnetic field suppresses the
acceleration of particles only when the guide field is stronger than the
alternating component. Our findings place important constraints on the models
of non-thermal radiation from Pulsar Wind Nebulae and relativistic jets.Comment: 25 pages, 14 figures, movies available at
https://www.cfa.harvard.edu/~lsironi/sironi_movies.tar ; in press, special
issue of Computational Science and Discovery on selected research from the
22nd International Conference on Numerical Simulation of Plasma
Three Dimensional Evolution of a Relativistic Current Sheet : Triggering of Magnetic Reconnection by the Guide Field
The linear and non-linear evolution of a relativistic current sheet of pair
() plasmas is investigated by three-dimensional particle-in-cell
simulations. In a Harris configuration, it is obtained that the magnetic energy
is fast dissipated by the relativistic drift kink instability (RDKI). However,
when a current-aligned magnetic field (the so-called "guide field") is
introduced, the RDKI is stabilized by the magnetic tension force and it
separates into two obliquely-propagating modes, which we call the relativistic
drift-kink-tearing instability (RDKTI). These two waves deform the current
sheet so that they trigger relativistic magnetic reconnection at a crossover
thinning point. Since relativistic reconnection produces a lot of non-thermal
particles, the guide field is of critical importance to study the energetics of
a relativistic current sheet.Comment: 12 pages, 4 figures; fixed typos and added a footnote [24
Model-based analyses of trends over time in the age corresponding to the transition phase for Antarctic minke whales in the JARPA research area
This study applies a model-based approach similar to that of Thomson et al. (1999) to the transition phase data obtained from JARPA surveys to examine trends in the age at maturity for the I and P stocks of Antarctic minke whales. The results, which takes into account various potential biases related to examining trend in transition phase data (i.e. truncation and fringe effects, differences between readers, and readers learning over time) suggest that the age at maturity of Antarctic minke whales declined from about 11 years in the late 1940s to 7 years in the late 1960s for both stocks, and these declining trends are statistically significant at the 5% level. The analyses also suggest that the age at maturity increased slightly from the late 1960s to the late 1970s and has stabilized thereafter. These trends are consistent with the results obtained from VPA (Mori et al. 2006), which suggest that for both the I and P stocks, abundance increased from the 1940s to the late 1960s and thereafter has been stable or declined somewhat. This consistency enhances the confidence to be placed in estimates of parameters (such as natural mortality and MSYR) from such VPA analyses that may be of value for management purposes. It also serves to demonstrate the utility of age-at-maturity as an index to monitor stock status, and suggests that continued monitoring of this parameter is desirable both for this purpose and for contributing to the understanding of the dynamics of the Antarctic ecosystem
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