5,211 research outputs found
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
The `Periodic Nulls' of Radio Pulsar J1819+1305
We present a single-pulse study of the four-component pulsar J1819+1305,
whose ``null'' pulses bunch at periodic intervals of around 57 times the
rotation period. The emission bursts between the null bunches exhibit
characteristic modulations at two shorter periodicities of approximately 6.2
and 3 times the rotation period, the former found largely in the two outer
components, and the latter only in the first component. Many bursts commence
with bright emission in second component, exhibit positive six-period drift
across the full profile width, and end with 3-period modulation in the leading
component. The 57-period cycle can be modelled geometrically as a sparsely
filled subbeam carousel with nulls appearing whenever our line of sight
intersects a circulating empty region. This interpretation is compatible with
other recent evidence for periodic, carousel-related nulling and appears to
support the physics of a polar-gap emission model for ``drifting'' subpulses,
but the subtle structure of the emission bursts defies an easy explanation.Comment: 8 pages, 9 figure
Drifting, moding, and nulling: another look at pulsar B1918+19
Arecibo observations of the conal triple pulsar B1918+19 at 0.327- and
1.4-GHz are used to analyse its subpulse behaviour in detail. We confirm the
presence of three distinct drift modes (A,B,C) plus a disordered mode (N) and
show that they follow one another in specific cycles. Interpreting the pulsar's
profile as resulting from a sightline traverse which cuts across an outer cone
and tangentially grazes an inner cone, we demonstrate that the phase modulation
of the inner cone is locked to the amplitude modulation of the outer cone in
all the drift modes. The 9% nulls are found to be largely confined to the
dominant B and N modes, and, in the N mode, create alternating bunches of nulls
and emission in a quasi-periodic manner with an averaged fluctuation rate of
about 12 rotation periods (). We explore the assumption that the apparent
drift is the first alias of a faster drift of subbeams equally spaced around
the cones. This is shown to imply that all modes A, B and C have a common
circulation time of 12 and differ only in the number of subbeams. This
timescale is on the same order as predicted by the classic {\bf E}{\bf
B} drift and also coincides with the N-mode modulation. We therefore arrive at
a picture where the circulation speed remains roughly invariant while the
subbeams progressively diminish in number from modes A to B to C, and are then
re-established during the N mode. We suggest that aliasing combined with
subbeam loss may be responsible for apparently dramatic changes in drift rates
in other pulsars
Is pulsar B0656+14 a very nearby RRAT source?
The recently discovered RRAT sources are characterized by very bright radio
bursts which, while being periodically related, occur infrequently. We find
bursts with the same characteristics for the known pulsar B0656+14. These
bursts represent pulses from the bright end of an extended smooth pulse-energy
distribution and are shown to be unlike giant pulses, giant micropulses or the
pulses of normal pulsars. The extreme peak-fluxes of the brightest of these
pulses indicates that PSR B0656+14, were it not so near, could only have been
discovered as an RRAT source. Longer observations of the RRATs may reveal that
they, like PSR B0656+14, emit weaker emission in addition to the bursts.Comment: 4 pages, 4 figures, accepted by ApJ
'Notches' in the Profiles of Bright Pulsars
We discuss the discovery of `notch-like' features in the mean pulse profile
of the nearby, bright pulsar B0950+08. We compare these low-level features with
those previously seen in the pulse profiles of pulsars J0437-4715 and B1929+10.
While J0437-4715 is a binary millisecond pulsar and B0950+08 and B1929+10 are
isolated, slow pulsars, all three pulsars are nearby and very bright.
Furthermore, all three have detectable emission over an unusually wide range of
pulse phase. We describe the similar properties of the notch features seen in
all three pulsars and discuss possible interpretations.Comment: 5 pages, 9 figures, submitted to MNRAS. See also astro-ph/031146
A deep campaign to characterize the synchronous radio/X-ray mode switching of PSR B0943+10
We report on simultaneous X-ray and radio observations of the mode-switching
pulsar PSR B0943+10 obtained with the XMM-Newton satellite and the LOFAR, LWA
and Arecibo radio telescopes in November 2014. We confirm the synchronous
X-ray/radio switching between a radio-bright (B) and a radio-quiet (Q) mode, in
which the X-ray flux is a factor ~2.4 higher than in the B-mode. We discovered
X-ray pulsations, with pulsed fraction of 38+/-5% (0.5-2 keV), during the
B-mode, and confirm their presence in Q-mode, where the pulsed fraction
increases with energy from ~20% up to ~65% at 2 keV. We found marginal evidence
for an increase in the X-ray pulsed fraction during B-mode on a timescale of
hours. The Q-mode X-ray spectrum requires a fit with a two-component model
(either a power-law plus blackbody or the sum of two blackbodies), while the
B-mode spectrum is well fit by a single blackbody (a single power-law is
rejected). With a maximum likelihood analysis, we found that in Q-mode the
pulsed emission has a thermal blackbody spectrum with temperature ~3.4x10^6 K
and the unpulsed emission is a power-law with photon index ~2.5, while during
B-mode both the pulsed and unpulsed emission can be fit by either a blackbody
or a power law with similar values of temperature and photon index. A Chandra
image shows no evidence for diffuse X-ray emission. These results support a
scenario in which both unpulsed non-thermal emission, likely of magnetospheric
origin, and pulsed thermal emission from a small polar cap (~1500 m^2) with a
strong non-dipolar magnetic field (~10^{14} G), are present during both radio
modes and vary in intensity in a correlated way. This is broadly consistent
with the predictions of the partially screened gap model and does not
necessarily imply global magnetospheric rearrangements to explain the mode
switching.Comment: To be published on The Astrophysical Journa
An Idealized Pulsar Magnetosphere: the Relativistic Force-Free Approximation
The non-dissipative relativistic force-free condition should be a good
approximation to describe the electromagnetic field in much of the pulsar
magnetosphere, but we may plausibly expect it to break down in singular
domains. Self-consistent magnetospheric solutions are found with field lines
closing both at and within the light-cylinder. In general, the detailed
properties of the solutions may be affected critically by the physics
determining the appropriate choice of equatorial boundary condition beyond the
light-cylinder.Comment: 31 pages, 3 figure
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