168 research outputs found
Probing fundamental physics with pulsars
Pulsars provide a wealth of information about General Relativity, the
equation of state of superdense matter, relativistic particle acceleration in
high magnetic fields, the Galaxy's interstellar medium and magnetic field,
stellar and binary evolution, celestial mechanics, planetary physics and even
cosmology. The wide variety of physical applications currently being
investigated through studies of radio pulsars rely on: (i) finding interesting
objects to study via large-scale and targeted surveys; (ii) high-precision
timing measurements which exploit their remarkable clock-like stability. We
review current surveys and the principles of pulsar timing and highlight
progress made in the rotating radio transients, intermittent pulsars, tests of
relativity, understanding pulsar evolution, measuring neutron star masses and
the pulsar timing array.Comment: 6 pages, 1 figure, to appear in the proceedings of IAU XXVII GA - JD3
- Neutron Stars: Timing in Extreme Environments XXVII IAU General Assembly,
Rio de Janeiro, Brazil, 3-14 August 200
A Study of Single Pulses in the Parkes Multibeam Pulsar Survey
We reprocessed the Parkes Multibeam Pulsar Survey, searching for single
pulses out to a DM of 5000 pc cm with widths of up to one second. We
recorded single pulses from 264 known pulsars and 14 Rotating Radio Transients.
We produced amplitude distributions for each pulsar which we fit with
log-normal distributions, power-law tails, and a power-law function divided by
an exponential function, finding that some pulsars show a deviation from a
log-normal distribution in the form of an excess of high-energy pulses. We
found that a function consisting of a power-law divided by an exponential fit
the distributions of most pulsars better than either log-normal or power-law
functions. For pulsars that were detected in a periodicity search, we computed
the ratio of their single-pulse signal-to-noise ratios to their signal-to-noise
ratios from a Fourier transform and looked for correlations between this ratio
and physical parameters of the pulsars. The only correlation found is the
expected relationship between this ratio and the spin period. Fitting
log-normal distributions to the amplitudes of pulses from RRATs showed similar
behaviour for most RRATs. Here, however, there seem to be two distinct
distributions of pulses, with the lower-energy distribution being consistent
with noise. Pulse-energy distributions for two of the RRATS processed were
consistent with those found for normal pulsars, suggesting that pulsars and
RRATs have a common emission mechanism, but other factors influence the
specific emission properties of each source class.Comment: 11 pages, 6 figures, 3 tables, accepted for publication in MNRA
X-ray and -ray Studies of the Millisecond Pulsar and Possible X-ray Binary/Radio Pulsar Transition Object PSR J1723-2837
We present X-ray observations of the "redback" eclipsing radio millisecond
pulsar and candidate radio pulsar/X-ray binary transition object PSR
J1723-2837. The X-ray emission from the system is predominantly non-thermal and
exhibits pronounced variability as a function of orbital phase, with a factor
of ~2 reduction in brightness around superior conjunction. Such temporal
behavior appears to be a defining characteristic of this variety of peculiar
millisecond pulsar binaries and is likely caused by a partial geometric
occultation by the main-sequence-like companion of a shock within the binary.
There is no indication of diffuse X-ray emission from a bow shock or pulsar
wind nebula associated with the pulsar. We also report on a search for point
source emission and -ray pulsations in Fermi Large Area Telescope data
using a likelihood analysis and photon probability weighting. Although PSR
J1723-2837 is consistent with being a -ray point source, due to the
strong Galactic diffuse emission at its position a definitive association
cannot be established. No statistically significant pulsations or modulation at
the orbital period are detected. For a presumed source detection, the implied
-ray luminosity is 5% of its spin-down power. This indicates
that PSR J1723-2837 is either one of the least efficient -ray producing
millisecond pulsars or, if the detection is spurious, the -ray emission
pattern is not directed towards us.Comment: 10 pages, 6 figures; accepted for publication in the Astrophysical
Journa
Systematic and Stochastic Variations in Pulsar Dispersion Measures
We analyze deterministic and random temporal variations in dispersion measure
(DM) from the full three-dimensional velocities of pulsars with respect to the
solar system, combined with electron-density variations on a wide range of
length scales. Previous treatments have largely ignored the pulsar's changing
distance while favoring interpretations involving the change in sky position
from transverse motion. Linear trends in pulsar DMs seen over 5-10~year
timescales may signify sizable DM gradients in the interstellar medium (ISM)
sampled by the changing direction of the line of sight to the pulsar. We show
that motions parallel to the line of sight can also account for linear trends,
for the apparent excess of DM variance over that extrapolated from
scintillation measurements, and for the apparent non-Kolmogorov scalings of DM
structure functions inferred in some cases. Pulsar motions through atomic gas
may produce bow-shock ionized gas that also contributes to DM variations. We
discuss possible causes of periodic or quasi-periodic changes in DM, including
seasonal changes in the ionosphere, annual variation of the solar elongation
angle, structure in the heliosphere-ISM boundary, and substructure in the ISM.
We assess the solar cycle's role on the amplitude of ionospheric and solar-wind
variations. Interstellar refraction can produce cyclic timing variations from
the error in transforming arrival times to the solar system barycenter. We
apply our methods to DM time series and DM gradient measurements in the
literature and assess consistency with a Kolmogorov medium. Finally, we discuss
the implications of DM modeling in precision pulsar timing experiments.Comment: 24 pages, 17 figures, published in Ap
No detectable radio emission from the magnetar-like pulsar in Kes 75
The rotation-powered pulsar PSR J1846-0258 in the supernova remnant Kes 75
was recently shown to have exhibited magnetar-like X-ray bursts in mid-2006.
Radio emission has not yet been observed from this source, but other
magnetar-like sources have exhibited transient radio emission following X-ray
bursts. We report on a deep 1.9 GHz radio observation of PSR J1846-0258 with
the 100-m Green Bank Telescope in late 2007 designed to search for radio
pulsations or bursts from this target. We have also analyzed three shorter
serendipitous 1.4 GHz radio observations of the source taken with the 64-m
Parkes telescope during the 2006 bursting period. We detected no radio emission
from PSR J1846-0258 in either the Green Bank or Parkes datasets. We place an
upper limit of 4.9 \mu Jy on coherent pulsed emission from PSR J1846-0258 based
on the 2007 November 2 observation, and an upper limit of 27 \mu Jy around the
time of the X-ray bursts. Serendipitously, we observed radio pulses from the
nearby RRAT J1846-02, and place a 3\sigma confidence level upper limit on its
period derivative of 1.7 * 10^{-13}, implying its surface dipole magnetic field
is less than 2.6 * 10^{13} G.Comment: 15 pages, 2 figures, submitted to Ap
A Simultaneous Dual-Frequency Scintillation Arc Survey of Six Bright Canonical Pulsars Using the Upgraded Giant Metrewave Radio Telescope
We use the Upgraded Giant Metrewave Radio Telescope to measure scintillation
arc properties in six bright canonical pulsars with simultaneous dual frequency
coverage. These observations at frequencies from 300 to 750 MHz allowed for
detailed analysis of arc evolution across frequency and epoch. We perform more
robust determinations of arc curvature, scattering delay, and scintillation
timescale frequency-dependence, and comparison between arc curvature and
pseudo-curvature than allowed by single-frequency-band-per-epoch measurements,
which we find to agree with theory and previous literature. We find a strong
correlation between arc asymmetry and arc curvature, which we have replicated
using simulations, and attribute to a bias in the Hough transform approach to
scintillation arc analysis. Possible evidence for an approximately week long
timescale over which a given scattering screen dominates signal propagation was
found by tracking visible scintillation arcs in each epoch in PSR J1136+1551.
The inclusion of a 155 minute observation allowed us to resolve the scale of
scintillation variations on short timescales, which we find to be directly tied
to the amount of ISM sampled over the observation. Some of our pulsars showed
either consistent or emerging asymmetries in arc curvature, indicating
instances of refraction across their lines of sight. Significant features in
various pulsars, such as multiple scintillation arcs in PSR J1136+1551 and flat
arclets in PSR J1509+5531, that have been found in previous works, were also
detected. The multiple band capability of the upgraded GMRT shows excellent
promise for future pulsar scintillation work
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