936 research outputs found
The geometry of the double-pulsar system J0737-3039 from systematic intensity variations
The recent discovery of J0737-3039A & B-two pulsars in a highly relativistic
orbit around one another - offers an unprecedented opportunity to study the
elusive physics of pulsar radio emission. The system contains a rapidly
rotating pulsar with a spin period of 22.7 ms and a slow companion with a spin
period of 2.77 s, hereafter referred to as 'A' and 'B', respectively. A unique
property of the system is that the pulsed radio flux from B increases
systematically by almost two orders-of-magnitude during two short portions of
each orbit. Here, we describe a geometrical model of the system that
simultaneously explains the intensity variations of B and makes definitive and
testable predictions for the future evolution of the emission properties of
both stars. Our model assumes that B's pulsed radio flux increases when
illuminated by emission from A. This model provides constraints on the spin
axis orientation and emission geometry of A and predicts that its pulse profile
will evolve considerably over the next several years due to geodetic precession
until it disappears entirely in 15-20 years
Observations of three slow glitches in the spin rate of the pulsar B1822-09
Three slow glitches in the rotation rate of the pulsar B1822-09 were revealed
over the 1995-2004 interval. The slow glitches observed are characterized by a
gradual increase in the rotation frequency with a long timescale of several
months, accompanied by a rapid decrease in the magnitude of the frequency first
derivative by 1-2 per cent of the initial value and subsequent exponential
increase back to its initial value on the same timescale. The cumulative
fractional increase in the pulsar rotation rate for the three glitches amounts
to Delta_nu/nu ~ 7 10^{-8}.Comment: 11 pages, 3 figures. Accepted for publication in MNRA
Discovery of 14 radio pulsars in a survey of the Magellanic Clouds
A systematic survey of the Large and Small Magellanic Clouds for radio
pulsars using the Parkes radio telescope and the 20-cm multibeam receiver has
resulted in the discovery of 14 pulsars and the redetection of five of the
eight previously known spin-powered pulsars believed to lie in the Magellanic
Clouds. Of the 14 new discoveries, 12 are believed to lie within Clouds, three
in the Small Cloud and nine in the Large Cloud, bringing the total number of
known spin-powered pulsars in the Clouds to 20. Averaged over all positions
within the survey area, the survey had a limiting flux density of about 0.12
mJy. Observed dispersion measures suggest that the mean free electron density
in the Magellanic Clouds is similar to that in the disk of our Galaxy. The
observed radio luminosities have little or no dependence on pulsar period or
characteristic age and the differential luminosity function is consistent with
a power-law slope of -1 as is observed for Galactic pulsars.Comment: In press, Ap
On the Excess Dispersion in the Polarization Position Angle of Pulsar Radio Emission
The polarization position angles (PA) of pulsar radio emission occupy a
distribution that can be much wider than what is expected from the average
linear polarization and the off-pulse instrumental noise. Contrary to our
limited understanding of the emission mechanism, the excess dispersion in PA
implies that pulsar PAs vary in a random fashion. An eigenvalue analysis of the
measured Stokes parameters is developed to determine the origin of the excess
PA dispersion. The analysis is applied to sensitive, well-calibrated
polarization observations of PSR B1929+10 and PSR B2020+28. The analysis
clarifies the origin of polarization fluctuations in the emission and reveals
that the excess PA dispersion is caused by the isotropic inflation of the data
point cluster formed by the measured Stokes parameters. The inflation of the
cluster is not consistent with random fluctuations in PA, as might be expected
from random changes in the orientation of the magnetic field lines in the
emission region or from stochastic Faraday rotation in either the pulsar
magnetosphere or the interstellar medium. The inflation of the cluster, and
thus the excess PA dispersion, is attributed to randomly polarized radiation in
the received pulsar signal. The analysis also indicates that orthogonal
polarization modes (OPM) occur where the radio emission is heavily modulated.
In fact, OPM may only occur where the modulation index exceeds a critical value
of about 0.3.Comment: Accepted for publication in Ap
Vela, its X-ray nebula, and the polarization of pulsar radiation
The recent identification of the perpendicular mode of radio polarization as
the primary one in the Vela pulsar by Lai et al. (2001) is interpreted in terms
of the maser mechanism proposed by Luo & Melrose (1995). We suggest that such a
mechanism may also be operative for the parallel mode which opens up the
possibility of accounting for all types of polarization observed in pulsars. We
propose an alternative interpretation of the arcs in the nebular X-radiation
observed by Pavlov et al.(2000) & Helfand et al. (2001) with the Chandra
Observatory, and interpreted by the latter as an equatorial wind. We interpret
the arcs as traces of the particle beams from the two magnetic poles at the
shock front. We also propose that the alignment with the rotation axis of the
jet-like feature bisecting the arcs is an effect of projection on the sky plane
and that there is no physical jet along the axis of rotation.Comment: 7 pages, 3 figures; version 2; accepted for publication in A&
Pair Multiplicities and Pulsar Death
Through a simple model of particle acceleration and pair creation above the
polar caps of rotation-powered pulsars, we calculate the height of the
pair-formation front (PFF) and the dominant photon emission mechanism for the
pulsars in the Princeton catalog. We find that for most low- and moderate-field
pulsars, the height of the pair formation front and the final Lorentz factor of
the primary beam is set by nonresonant inverse Compton scattering (NRICS), in
the Klein-Nishina limit. NRICS is capable of creating pairs over a wide range
of pulsar parameters without invoking a magnetic field more complicated than a
centered dipole, although we still require a reduced radius of curvature for
most millisecond pulsars. For short-period pulsars, the dominant process is
curvature radiation, while for extremely high-field pulsars, it is resonant
inverse Compton scattering (RICS). The dividing point between NRICS dominance
and curvature dominance is very temperature-dependent; large numbers of pulsars
dominated by NRICS at a stellar temperature of K are dominated by
curvature at K. We apply these results to pulsar death-line calculations
and to the issue of particle injection into the Crab Nebula.Comment: 14 pages, 7 figures, to appear in Ap
Glitches in Southern Pulsars
Timing observations of 40 mostly young pulsars using the ATNF Parkes radio
telescope between 1990 January and 1998 December are reported. In total, 20
previously unreported glitches and ten other glitches were detected in 11
pulsars. These included 12 glitches in PSR J13416220, corresponding to a
glitch rate of 1.5 glitches per year. We also detected the largest known
glitch, in PSR J16145047, with
where is the pulse frequency. Glitch parameters were determined
both by extrapolating timing solutions to inter-glitch intervals and by
phase-coherent timing fits across the glitch(es). Analysis of glitch
parameters, both from this work and from previously published results, shows
that most glitches have a fractional amplitude of between
and . There is no consistent relationship between glitch
amplitude and the time since the previous glitch or the time to the following
glitch, either for the ensemble or for individual pulsars. As previously
recognised, the largest glitch activity is seen in pulsars with ages of order
10 years, but for about 30 per cent of such pulsars, no glitches were
detected in the 8-year data span. There is some evidence for a new type of
timing irregularity in which there is a significant increase in pulse frequency
over a few days, accompanied by a decrease in the magnitude of the slowdown
rate. Fits of an exponential recovery to post-glitch data show that for most
older pulsars, only a small fraction of the glitch decays. In some younger
pulsars, a large fraction of the glitch decays, but in others, there is very
little decay.Comment: 19 pages, 20 figures. Accepted for publication in MNRA
Pulsar Radio Emission Altitude from Curvature Radiation
We assume that the relativistic sources moving along the dipolar magnetic
field lines emit curvature radiation. The beamed emission occurs in the
direction of tangents to the field lines, and to receive it, the sight line
must align with the tangent within the beaming angle 1/gamma, where gamma is
the particle Lorentz factor. By solving the viewing geometry in an inclined and
rotating dipole magnetic field, we show that, at any given pulse phase,
observer tends to receive radiation only from the specific heights allowed by
the geometry. We find outer conal components are emitted at higher altitudes
compared to inner components including the core. At any pulse phase, low
frequency emission comes from higher altitudes than high frequency emission. We
have modeled the emission heights of pulse components of PSR B0329+54, and
estimated field line curvature radii and particle Lorentz factors in the
emission regions.Comment: 14 pages, 3 figures. Accepted for Astrophysical Journal, 200
High time-resolution observations of the Vela pulsar
We present high time resolution observations of single pulses from the Vela
pulsar (PSR B0833-45) made with a baseband recording system at observing
frequencies of 660 and 1413 MHz. We have discovered two startling features in
the 1413 MHz single pulse data. The first is the presence of giant micro-pulses
which are confined to the leading edge of the pulse profile. One of these
pulses has a peak flux density in excess of 2500 Jy, more than 40 times the
integrated pulse peak. The second new result is the presence of a large
amplitude gaussian component on the trailing edge of the pulse profile. This
component can exceed the main pulse in intensity but is switched on only
relatively rarely. Fluctutation spectra reveal a possible periodicity in this
feature of 140 pulse periods. Unlike the rest of the profile, this component
has low net polarization and emits predominantly in the orthogonal mode. This
feature appears to be unique to the Vela pulsar. We have also detected
microstructure in the Vela pulsar for the first time. These same features are
present in the 660 MHz data. We suggest that the full width of the Vela pulse
profile might be as large as 10 ms but that the conal edges emit only rarely.Comment: 6 pages, 5 figures, In Press with ApJ Letter
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