801 research outputs found
Topology and Polarisation of Subbeams Associated With Pulsar 0943+10's ``Drifting''-Subpulse Emission: I. Analysis of Arecibo 430- and 111-MHz Observations
The ``drifting'' subpulses exhibited by some radio pulsars have fascinated
both observers and theorists for 30 years, and have been widely regarded as one
of the most critical and potentially insightful aspects of their emission.
Here, we report on detailed studies of pulsar B0943+10, whose nearly coherent
sequences of ``drifting'' subpulses have permitted us to identify their origin
as a system of subbeams that appear to circulate around the star's magnetic
axis. We introduce several new techniques of analysis, and we find that both
the primary and secondary features in the star's fluctuation spectra are
aliases of their actual values. We have also developed a method of tracing the
underlying pattern responsible for the observed sequences, using a
``cartographic'' transform and its inverse, permitting us to study the
characteristics of the polar-cap emission ``map'' and to confirm that such a
``map'' in turn represents the observed sequence. We apply these techniques to
the study of three different Arecibo observations. The ``B''-mode sequences are
consistent in revealing that the emission pattern consists of 20 subbeams,
which rotate around the magnetic axis in about 37 periods or 41 seconds. Even
in the ``Q'' mode sequence, we find evidence of a compatible circulation time.
The similarity of the subbeam patterns at different radio frequencies strongly
suggests that the radiation is produced within a set of columns, which extend
from close to the stellar surface up though the emission region and reflect
some manner of a ``seeding''phenomenon at their base. The subbeam emission is
then tied neither to the stellar surface nor to the field.Comment: 25 pages with 26 figures; in press in MNRA
Circulating Subbeam Systems and the Physics of Pulsar Emission
The purpose of this paper is to suggest how detailed single-pulse
observations of ``slow'' radio pulsars may be utilized to construct an
empirical model for their emission. It links the observational synthesis
developed in a series of papers by Rankin starting in the 1980s to the more
recent empirical feedback model of Wright (2003a) by regarding the entire
pulsar magnetosphere as a non-steady, non-linear interactive system with a
natural built-in delay. It is argued that the enhanced role of the outer gap in
such a system indicates an evolutionary link to younger pulsars, in which this
region is thought to be highly active, and that pulsar magnetospheres should no
longer be seen as being ``driven'' by events on the neutron star's polar cap,
but as having more in common with planetary magnetospheres and auroral
phenomena.Comment: 15 pages, 3 figure
On the long and short nulls, modes and interpulse emission of radio pulsar B1944+17
We present a single pulse study of pulsar B1944+17, whose non-random nulls
dominate nearly 70% of its pulses and usually occur at mode boundaries. When
not in the null state, this pulsar displays four bright modes of emission,
three of which exhibit drifting subpulses. B1944+17 displays a weak interpulse
whose position relative to the main pulse we find to be frequency independent.
Its emission is nearly 100% polarized, its polarization-angle traverse is very
shallow and opposite in direction to that of the main pulse, and it nulls
approximately two-thirds of the time. Geometric modeling indicates that this
pulsar is a nearly aligned rotator whose alpha value is hardly 2 degrees--i.e.,
its magnetic axis is so closely aligned with its rotation axis that its
sightline orbit remains within its conal beam. The star's nulls appear to be of
two distinct types: those with lengths less than about 8 rotation periods
appear to be pseudonulls--that is, produced by "empty" sightline traverses
through the conal beam system; whereas the longer nulls appear to represent
actual cessations of the pulsar's emission engine
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