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[show abstract]
[hide abstract]
ABSTRACT: Next-generation radio arrays, including the SKA and its pathfinders, will
open up new avenues for exciting transient science at radio wavelengths. Their
innovative designs, comprising a large number of small elements, pose several
challenges in digital processing and optimal observing strategies. The Giant
Metre-wave Radio Telescope (GMRT)presents an excellent test-bed for developing
and validating suitable observing modes and strategies for transient
experiments with future arrays. Here we describe the first phase of the ongoing
development of a transient detection system for GMRT that is planned to
eventually function in a commensal mode with other observing programs. It
capitalizes on the GMRT's interferometric and sub-array capabilities, and the
versatility of a new software backend. We outline considerations in the plan
and design of transient exploration programs with interferometric arrays, and
describe a pilot survey that was undertaken to aid in the development of
algorithms and associated analysis software. This survey was conducted at 325
and 610 MHz, and covered 360 deg$^2$ of the sky with short dwell times. It
provides large volumes of real data that can be used to test the efficacies of
various algorithms and observing strategies applicable for transient detection.
We present examples that illustrate the methodologies of detecting
short-duration transients, including the use of sub-arrays for higher
resilience to spurious events of terrestrial origin, localization of candidate
events via imaging and the use of a phased array for improved signal detection
and confirmation. In addition to demonstrating applications of interferometric
arrays for fast transient exploration, our efforts mark important steps in the
roadmap toward SKA-era science.
02/2013;
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M. J. Keith,
W. Coles,
R. M. Shannon,
G. B. Hobbs,
R. N. Manchester, M. Bailes,
N. D. R. Bhat,
S. Burke-Spolaor,
D. J. Champion,
A. Chaudhary,
A. W. Hotan,
J. Khoo,
J. Kocz,
S. Oslowski,
V. Ravi,
J. E. Reynolds,
J. Sarkissian,
W. van Straten,
D. R. B. Yardley
[show abstract]
[hide abstract]
ABSTRACT: Signals from radio pulsars show a wavelength-dependent delay due to
dispersion in the interstellar plasma. At a typical observing wavelength, this
delay can vary by tens of microseconds on five-year time scales, far in excess
of signals of interest to pulsar timing arrays, such as that induced by a
gravitational-wave background. Measurement of these delay variations is not
only crucial for the detection of such signals, but also provides an
unparallelled measurement of the turbulent interstellar plasma at au scales. In
this paper we demonstrate that without consideration of wavelength- independent
red-noise, 'simple' algorithms to correct for interstellar dispersion can
attenuate signals of interest to pulsar timing arrays. We present a robust
method for this correction, which we validate through simulations, and apply it
to observations from the Parkes Pulsar Timing Array. Correction for dispersion
variations comes at a cost of increased band-limited white noise. We discuss
scheduling to minimise this additional noise, and factors, such as
scintillation, that can exacerbate the problem. Comparison with scintillation
measurements confirms previous results that the spectral exponent of electron
density variations in the interstellar medium often appears steeper than
expected. We also find a discrete change in dispersion measure of PSR
J1603-7202 of ~2x10^{-3} cm^{-3}pc for about 250 days. We speculate that this
has a similar origin to the 'extreme scattering events' seen in other sources.
In addition, we find that four pulsars show a wavelength-dependent annual
variation, indicating a persistent gradient of electron density on an au
spatial scale, which has not been reported previously.
11/2012;
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R. N. Manchester,
G. Hobbs, M. Bailes,
W. A. Coles,
W. van Straten,
M. J. Keith,
R. M. Shannon,
N. D. R. Bhat,
A. Brown,
S. G. Burke-Spolaor, [......],
S. Oslowski,
V. Ravi,
J. R. Reynolds,
J. M. Sarkissian,
J. P. W. Verbiest,
Z. L. Wen,
W. E. Wilson,
D. Yardley,
W. M. Yan,
X. P. You
[show abstract]
[hide abstract]
ABSTRACT: A "pulsar timing array" (PTA), in which observations of a large sample of
pulsars spread across the celestial sphere are combined, allows investigation
of "global" phenomena such as a background of gravitational waves or
instabilities in atomic timescales that produce correlated timing residuals in
the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an
implementation of the PTA concept based on observations with the Parkes 64-m
radio telescope. A sample of 20 millisecond pulsars is being observed at three
radio-frequency bands, 50cm (~700 MHz), 20cm (~1400 MHz) and 10cm (~3100 MHz),
with observations at intervals of 2 - 3 weeks. Regular observations commenced
in early 2005. This paper describes the systems used for the PPTA observations
and data processing, including calibration and timing analysis. The strategy
behind the choice of pulsars, observing parameters and analysis methods is
discussed. Results are presented for PPTA data in the three bands taken between
2005 March and 2011 March. For ten of the 20 pulsars, rms timing residuals are
less than 1 microsec for the best band after fitting for pulse frequency and
its first time derivative. Significant "red" timing noise is detected in about
half of the sample. We discuss the implications of these results on future
projects including the International Pulsar Timing Array (IPTA) and a PTA based
on the Square Kilometre Array. We also present an "extended PPTA" data set that
combines PPTA data with earlier Parkes timing data for these pulsars.
10/2012;
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A. Corongiu,
M. Burgay,
A. Possenti,
F. Camilo,
N. D'Amico,
A. G. Lyne,
R. N. Manchester,
J. M. Sarkissian, M. Bailes,
S. Johnston,
M. Kramer,
W. van Straten
[show abstract]
[hide abstract]
ABSTRACT: PSR J1910-5959A is a binary pulsar with a helium white dwarf companion
located about 6 arcmin from the center of the globular cluster NGC6752. Based
on 12 years of observations at the Parkes radio telescope, the relativistic
Shapiro delay has been detected in this system. We obtain a companion mass Mc =
0.180+/-0.018Msun (1sigma) implying that the pulsar mass lies in the range
1.1Msun <= Mp <= 1.5Msun. We compare our results with previous optical
determinations of the companion mass, and examine prospects for using this new
measurement for calibrating the mass-radius relation for helium white dwarfs
and for investigating their evolution in a pulsar binary system. Finally we
examine the set of binary systems hosting a millisecond pulsar and a low mass
helium white dwarf for which the mass of both stars has been measured. We
confirm that the correlation between the companion mass and the orbital period
predicted by Tauris & Savonije reproduces the observed values but find that the
predicted Mp - Pb correlation over-estimates the neutron star mass by about
0.5Msun in the orbital period range covered by the observations. Moreover, a
few systems do not obey the observed Mp - Pb correlation. We discuss these
results in the framework of the mechanisms that inhibit the accretion of matter
by a neutron star during its evolution in a low-mass X-ray binary.
10/2012;
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[show abstract]
[hide abstract]
ABSTRACT: Pulsars in close binary systems have provided some of the most stringent
tests of strong-field gravity to date. The pulsar--white-dwarf binary system
J1141-6545 is specifically interesting due to its gravitational asymmetry which
makes it one of the most powerful probes of tensor-scalar theories of gravity.
We give an overview of current gravitational tests provided by the J1141-6545
binary system and comment on how anomalous accelerations, geodetic precession
and timing instabilities may be prevented from limiting future tests of gravity
to come from this system.
09/2012;
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S. D. Bates, M. Bailes,
B. R. Barsdell,
N. D. R. Bhat,
M. Burgay,
S. Burke-Spolaor,
D. J. Champion,
P. Coster,
N. D'Amico,
A. Jameson, [......],
M. Kramer,
L. Levin,
A. Lyne,
S. Milia,
C. Ng,
C. Nietner,
A. Possenti,
B. Stappers,
D. Thornton,
W. van Straten
[show abstract]
[hide abstract]
ABSTRACT: We present 75 pulsars discovered in the mid-latitude portion of the High Time
Resolution Universe survey, 54 of which have full timing solutions. All the
pulsars have spin periods greater than 100 ms, and none of those with timing
solutions are in binaries. Two display particularly interesting behaviour; PSR
J1054-5944 is found to be an intermittent pulsar, and PSR J1809-0119 has
glitched twice since its discovery.
In the second half of the paper we discuss the development and application of
an artificial neural network in the data-processing pipeline for the survey. We
discuss the tests that were used to generate scores and find that our neural
network was able to reject over 99% of the candidates produced in the data
processing, and able to blindly detect 85% of pulsars. We suggest that
improvements to the accuracy should be possible if further care is taken when
training an artificial neural network; for example ensuring that a
representative sample of the pulsar population is used during the training
process, or the use of different artificial neural networks for the detection
of different types of pulsars.
09/2012;
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G. Hobbs,
W. Coles,
R. N. Manchester,
M. J. Keith,
R. M. Shannon,
D. Chen, M. Bailes,
N. D. R. Bhat,
S. Burke-Spolaor,
D. Champion, [......],
Y. Levin,
S. Oslowski,
B. Preisig,
V. Ravi,
J. E. Reynolds,
J. Sarkissian,
W. van Straten,
J. P. W. Verbiest,
D. Yardley,
X. P. You
[show abstract]
[hide abstract]
ABSTRACT: Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA)
project we develop the first pulsar-based timescale that has a precision
comparable to the uncertainties in international atomic timescales. Our
ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the
free atomic timescale Echelle Atomique Libre (EAL). The EPS can be used to
detect fluctuations in atomic timescales and therefore can lead to a new
realisation of Terrestrial Time, TT(PPTA11). We successfully follow features
known to affect the frequency of the International Atomic Timescale (TAI) and
we find marginally significant differences between TT(PPTA11) and TT(BIPM11).
We discuss the various phenomena that lead to a correlated signal in the pulsar
timing residuals and therefore limit the stability of the pulsar timescale.
08/2012;
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W. M. Yan,
R. N. Manchester,
G. Hobbs,
W. van Straten,
J. E. Reynolds,
N. Wang, M. Bailes,
N. D. R. Bhat,
S. Burke-Spolaor,
D. J. Champion,
A. Chaudhary,
W. A. Coles,
A. W. Hotan,
J. Khoo,
S. Oslowski,
J. M. Sarkissian,
D. R. B. Yardley
[show abstract]
[hide abstract]
ABSTRACT: We report on variations in the mean position angle of the 20 millisecond pulsars being observed as part of the Parkes Pulsar
Timing Array (PPTA) project. It is found that the observed variations are dominated by changes in the Faraday rotation occurring
in the Earth’s ionosphere. Two ionospheric models are used to correct for the ionospheric contribution and it is found that
one based on the International Reference Ionosphere gave the best results. Little or no significant long-term variation in
interstellar RM was found with limits typically about 0.1rad m−2 yr−1 in absolute value. In a few cases, apparently significant RM variations over timescales of a few 100 days or more were seen.
These are unlikely to be due to localised magnetised regions crossing the line of sight since the implied magnetic fields
are too high. Most probably they are statistical fluctuations due to random spatial and temporal variations in the interstellar
electron density and magnetic field along the line of sight.
KeywordsPulsars: general–ISM: general–Radio continuum: stars
Astrophysics and Space Science 04/2012; 335(2):485-498. · 1.69 Impact Factor
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S. Johnston,
R. Taylor, M. Bailes,
N. Bartel,
C. Baugh,
M. Bietenholz,
C. Blake,
R. Braun,
J. Brown,
S. Chatterjee, [......],
E. Sadler,
B. Schmidt,
I. Stairs,
L. Staveley-Smith,
J. Stil,
S. Tingay,
A. Tzioumis,
M. Walker,
J. Wall,
M. Wolleben
[show abstract]
[hide abstract]
ABSTRACT: The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium
of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for
the SKA will be addressed through large-area imaging of the Universe at frequencies from 300MHz to a few GHz. The Australian
SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the
development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented
synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at
the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of
the sites selected by the international community as a potential location for the SKA. Following an introductory description
of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP. In summary, the goals of these
programmes are as follows:
–
The detection of a million galaxies in atomic hydrogen emission across 75% of the sky out to a redshift of 0.2 to understand
galaxy formation and gas evolution in the nearby Universe.
–
The detection of synchrotron radiation from 60 million galaxies to determine the evolution, formation and population of galaxies
across cosmic time and enabling key cosmological tests.
–
The detection of polarized radiation from over 500,000 galaxies, allowing a grid of rotation measures at 10′ to explore the
evolution of magnetic fields in galaxies over cosmic time.
–
The understanding of the evolution of the interstellar medium of our own Galaxy and the processes that drive its chemical
and physical evolution.
–
The high-resolution imaging of intense, energetic phenomena by enlarging the Australian and global Very Long Baseline networks.
–
The discovery and timing of a thousand new radio pulsars.
–
The characterization of the radio transient sky through detection and monitoring of transient sources such as gamma ray bursts,
radio supernovae and intra-day variables.
The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading
radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter
emphasizes the point, and considers discovery space.
Experimental Astronomy 04/2012; 22(3):151-273. · 1.82 Impact Factor
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L. Levin, M. Bailes,
S. D. Bates,
N. D. R. Bhat,
M. Burgay,
S. Burke-Spolaor,
N. D'Amico,
S. Johnston,
M. J. Keith,
M. Kramer,
S. Milia,
A. Possenti,
B. Stappers,
W. van Straten
[show abstract]
[hide abstract]
ABSTRACT: Here we report on observations of the radio magnetar PSR J1622-4950 at
frequencies from 1.4 to 17 GHz. We show that although its flux density is
varying up to a factor of ~10 within a few days, it has on average decreased by
a factor of 2 over the last 700 days. At the same time, timing analysis
indicates a trend of decreasing spin-down rate over our entire data set, again
of about a factor of 2 over 700 days, but also an erratic variability in the
spin-down rate within this time span. Integrated pulse profiles are often close
to 100 per cent linearly polarized, but large variations in both the profile
shape and fractional polarization are regularly observed. Furthermore, the
behaviour of the position angle of the linear polarization is very complex -
offsets in both the absolute position angle and the phase of the position angle
sweep are often seen and the occasional presence of orthogonal mode jumps
further complicates the picture. However, model fitting indicates that the
magnetic and rotation axes are close to aligned. Finally, a single pulse
analysis has been carried out at four observing frequencies, demonstrating that
the wide pulse profile is built up of narrow spikes of emission, with widths
that scale inversely with observing frequency. All three of the known radio
magnetars seem to have similar characteristics, with highly polarized emission,
time-variable flux density and pulse profiles, and with spectral indices close
to zero.
04/2012;
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S. Burke-Spolaor,
S. Johnston, M. Bailes,
S. D. Bates,
N. D. R. Bhat,
M. Burgay,
D. J. Champion,
N. D'Amico,
M. J. Keith,
M. Kramer,
L. Levin,
S. Milia A. Possenti,
B. Stappers,
W. van Straten
[show abstract]
[hide abstract]
ABSTRACT: We report on the pulse-to-pulse energy distributions and phase-resolved
modulation properties for catalogued pulsars in the southern High Time
Resolution Universe intermediate-latitude survey. We selected the 315 pulsars
detected in a single-pulse search of this survey, allowing a large sample
unbiased regarding any rotational parameters of neutron stars. We found that
the energy distribution of many pulsars is well-described by a log-normal
distribution, with few deviating from a small range in log-normal scale and
location parameters. Some pulsars exhibited multiple energy states
corresponding to mode changes, and implying that some observed "nulling" may
actually be a mode-change effect. PSRJ1900-2600 was found to emit weakly in its
previously-identified "null" state. We found evidence for another state-change
effect in two pulsars, which show bimodality in their nulling time scales; that
is, they switch between a continuous-emission state and a single-pulse-emitting
state. Large modulation occurs in many pulsars across the full integrated
profile, with increased sporadic bursts at leading and trailing sub-beam edges.
Some of these high-energy outbursts may indicate the presence of "giant pulse"
phenomena. We found no correlation with modulation and pulsar period, age, or
other parameters. Finally, the deviation of integrated pulse energy from its
average value was generally quite small, despite the significant phase-resolved
modulation in some pulsars; we interpret this as tenuous evidence of energy
regulation between distinct pulsar sub-beams.
03/2012;
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M. J. Keith,
S. Johnston, M. Bailes,
S. D. Bates,
N. D. R. Bhat,
M. Burgay,
S. Burke-Spolaor,
N. D’Amico,
A. Jameson,
M. Kramer,
L. Levin,
S. Milia,
A. Possenti,
B. W. Stappers,
W. van Straten,
D. Parent
[show abstract]
[hide abstract]
ABSTRACT: We present the discovery of six millisecond pulsars (MSPs) in the High Time Resolution Universe (HTRU) survey for pulsars and fast transients carried out with the Parkes radio telescope. All six are in binary systems with approximately circular orbits and are likely to have white dwarf companions. PSR J1017−7156 has a high flux density and a narrow pulse width, making it ideal for precision timing experiments. PSR J1446−4701 and PSR J1125−5825 are coincident with gamma-ray sources, and folding the high-energy photons with the radio timing ephemeris shows evidence of pulsed gamma-ray emission. PSR J1502−6752 has a spin period of 26.7 ms, and its low period derivative implies that it is a recycled pulsar. The orbital parameters indicate it has a very low mass function, and therefore a companion mass much lower than usually expected for such a mildly recycled pulsar.In addition we present polarization profiles for all 12 MSPs discovered in the HTRU survey to date. Similar to previous observations of MSPs, we find that many have large widths and a wide range of linear and circular polarization fractions. Their polarization profiles can be highly complex, and although the observed position angles often do not obey the rotating vector model, we present several examples of those that do. We speculate that the emission heights of MSPs are a substantial fraction of the light cylinder radius in order to explain broad emission profiles, which then naturally leads to a large number of cases where emission from both poles is observed.
Monthly Notices of the Royal Astronomical Society 01/2012; 419(2):1752 - 1765. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We demonstrate that the sensitivity of high-precision pulsar timing experiments will be ultimately limited by the broad-band intensity modulation that is intrinsic to the pulsar’s stochastic radio signal. That is, as the peak flux of the pulsar approaches that of the system equivalent flux density, neither greater antenna gain nor increased instrumental bandwidth will improve timing precision. These conclusions proceed from an analysis of the covariance matrix used to characterize residual pulse profile fluctuations following the template-matching procedure for arrival time estimation. We perform such an analysis on 25 h of high-precision timing observations of the closest and brightest millisecond pulsar, PSR J0437−4715. In these data, the standard deviation of the post-fit arrival time residuals is approximately four times greater than that predicted by considering the system equivalent flux density, mean pulsar flux and the effective width of the pulsed emission. We develop a technique based on principal component analysis to mitigate the effects of shape variations on arrival time estimation and demonstrate its validity using a number of illustrative simulations. When applied to our observations, the method reduces arrival time residual noise by approximately 20 per cent. We conclude that, owing primarily to the intrinsic variability of the radio emission from PSR J0437−4715 at 20 cm, timing precision in this observing band better than 30–40 ns in 1 h is highly unlikely, regardless of future improvements in antenna gain or instrumental bandwidth. We describe the intrinsic variability of the pulsar signal as stochastic wide-band impulse modulated self-noise (SWIMS) and argue that SWIMS will likely limit the timing precision of every millisecond pulsar currently observed by pulsar timing array projects as larger and more sensitive antennas are built in the coming decades.
Monthly Notices of the Royal Astronomical Society 11/2011; 418(2):1258 - 1271. · 4.90 Impact Factor
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S. D. Bates, M. Bailes,
N. D. R. Bhat,
M. Burgay,
S. Burke-Spolaor,
N. D’Amico,
A. Jameson,
S. Johnston,
M. J. Keith,
M. Kramer,
L. Levin,
A. Lyne,
S. Milia,
A. Possenti,
B. Stappers,
W. van Straten
[show abstract]
[hide abstract]
ABSTRACT: We present the discovery of five millisecond pulsars found in the mid-Galactic latitude portion of the High Time Resolution Universe (HTRU) survey. The pulsars have rotational periods from ∼2.3 ms to ∼7.5 ms, and all are in binary systems with orbital periods ranging from ∼0.3 to ∼150 d. In four of these systems, the most likely companion is a white dwarf, with minimum masses of ∼0.2 M⊙. The other pulsar, J1731−1847, has a very low mass companion and exhibits eclipses and is thus a member of the ‘black widow’ class of pulsar binaries. These eclipses have been observed in bands centred near frequencies of 700, 1400 and 3000 MHz, from which measurements have been made of the electron density in the eclipse region. These measurements have been used to examine some possible eclipse mechanisms. The eclipse and other properties of this source are used to perform a comparison with the other known eclipsing and ‘black widow’ pulsars.These new discoveries occupy a short-period and high-dispersion measure (DM) region of parameter space, which we demonstrate is a direct consequence of the high time and frequency resolution of the HTRU survey. The large implied distances to our new discoveries make observation of their companions unlikely with both current optical telescopes and the Fermi Gamma-ray Space Telescope. The extremely circular orbits make any advance of periastron measurements highly unlikely. No relativistic Shapiro delays are obvious in any of the systems although the low flux densities would make their detection difficult unless the orbits were fortuitously edge-on.
Monthly Notices of the Royal Astronomical Society 09/2011; 416(4):2455 - 2464. · 4.90 Impact Factor
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S. Burke-Spolaor, M. Bailes,
S. Johnston,
S. D. Bates,
N. D. R. Bhat,
M. Burgay,
N. D’Amico,
A. Jameson,
M. J. Keith,
M. Kramer,
L. Levin,
S. Milia,
A. Possenti,
B. Stappers,
W. van Straten
[show abstract]
[hide abstract]
ABSTRACT: We present the search methods and initial results for transient radio signals in the High Time Resolution Universe (HTRU) survey. The HTRU survey’s single-pulse search, the software designed to perform the search and a determination of the HTRU survey’s sensitivity to single pulses are described. Initial processing of a small fraction of the survey has produced 11 discoveries, all of which are sparsely emitting neutron stars, as well as provided confirmation of two previously unconfirmed neutron stars. Most of the newly discovered objects lie in regions surveyed previously, indicating both the improved sensitivity of the HTRU survey observing system and the dynamic nature of the radio sky. The cycles of active and null states in nulling pulsars, rotating radio transients (RRATs) and long-term intermittent pulsars are explored in the context of determining the relationship between these populations and of the sensitivity of a search to the various radio-intermittent neutron star populations. This analysis supports the case that many RRATs are in fact high-null-fraction pulsars (i.e. with a null fraction of ≳0.95) and indicates that intermittent pulsars appear distinct from nulling pulsars in their activity cycle time-scales. We find that in the measured population, there is a deficit of pulsars with typical emission time-scales greater than ∼300 s that is not readily explained by selection effects. The HTRU low-latitude survey will be capable of addressing whether this deficit is physical. We predict that the HTRU survey will explore pulsars with a broad range of nulling fractions (up to and beyond 0.999), and at its completion is likely to increase the currently known RRATs by a factor of more than 2.
Monthly Notices of the Royal Astronomical Society 09/2011; 416(4):2465 - 2476. · 4.90 Impact Factor
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M Bailes,
S D Bates,
V Bhalerao,
N D R Bhat,
M Burgay,
S Burke-Spolaor,
N D'Amico,
S Johnston,
M J Keith,
M Kramer,
S R Kulkarni,
L Levin,
A G Lyne,
S Milia,
A Possenti,
L Spitler,
B Stappers,
W van Straten
[show abstract]
[hide abstract]
ABSTRACT: Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction.
Science 08/2011; 333(6050):1717-20. · 31.20 Impact Factor
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W. M. Yan,
R. N. Manchester,
W. van Straten,
J. E. Reynolds,
G. Hobbs,
N. Wang, M. Bailes,
N. D. R. Bhat,
S. Burke-Spolaor,
D. J. Champion,
W. A. Coles,
A. W. Hotan,
J. Khoo,
S. Oslowski,
J. M. Sarkissian,
J. P. W. Verbiest,
D. R. B. Yardley
[show abstract]
[hide abstract]
ABSTRACT: Polarization profiles are presented for 20 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The observations used the Parkes multibeam receiver with a central frequency of 1369 MHz and the Parkes digital filter bank pulsar signal-processing system PDFB2. Because of the large total observing time, the summed polarization profiles have very high signal-to-noise ratios and show many previously undetected profile features. 13 of the 20 pulsars show emission over more than half of the pulse period. Polarization variations across the profiles are complex, and the observed position angle variations are generally not in accord with the rotating vector model for pulsar polarization. Nevertheless, the polarization properties are broadly similar to those of normal (non-millisecond) pulsars, suggesting that the basic radio emission mechanism is the same in both classes of pulsar. The results support the idea that radio emission from millisecond pulsars originates high in the pulsar magnetosphere, probably close to the emission regions for high-energy X-ray and gamma-ray emission. Rotation measures were obtained for all 20 pulsars, eight of which had no previously published measurements.
Monthly Notices of the Royal Astronomical Society 06/2011; 414(3):2087 - 2100. · 4.90 Impact Factor
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G. Hobbs,
D Miller,
R. N. Manchester,
J. Dempsey,
J M Chapman,
J. Khoo,
J. Applegate, M. Bailes,
N. D. R. Bhat,
R. Bridle, [......],
J Morrissey,
M. Pienaar,
J. Reynolds,
G. Ryder,
J. Sarkissian,
A. Stevenson,
A. Treloar,
W. van Straten,
M. Whiting,
G Wilson
[show abstract]
[hide abstract]
ABSTRACT: The Parkes pulsar data archive currently provides access to 144044 data files
obtained from observations carried out at the Parkes observatory since the year
1991. Around 10^5 files are from surveys of the sky, the remainder are
observations of 775 individual pulsars and their corresponding calibration
signals. Survey observations are included from the Parkes 70cm and the
Swinburne Intermediate Latitude surveys. Individual pulsar observations are
included from young pulsar timing projects, the Parkes Pulsar Timing Array and
from the PULSE@Parkes outreach program. The data files and access methods are
compatible with Virtual Observatory protocols. This paper describes the data
currently stored in the archive and presents ways in which these data can be
searched and downloaded.
05/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present observations of PSRs J0437-4715, J0738-4042, J0835-4510,
J0908-4913, J1048-5832, J1622-4950, J1644-4559, J1721-3532 and J1740-3015 at 17
GHz using the Parkes radio telescope. All 9 were detected at 17 GHz,
additionally, we detected PSR J0835-4510 and J1622-4950 at 24 GHz. Polarisation
profiles of each pulsar and the variation with frequency are discussed. In
general, we find that the highly polarised edge components of young pulsars
continue to dominate their profiles at 17 GHz. Older pulsars (>10^5 years)
appear to be almost completely depolarised. Our detection of PSR J0437-4715 is
the highest frequency observation of a millisecond pulsar to date, and implies
a luminosity at 17 GHz of 14 {\mu}Jy kpc^2, and a mean spectral index of 2.2.
We find that the spectral index of the magnetar PSR J1622-4950 is flat between
1.4 and 24 GHz, similar to the other known radio magnetars XTE J1810-197 and 1E
1547.0-5408. The profile is similar to that at 3.1 GHz, and is highly linearly
polarised. Analysis of the frequency evolution of the profile of PSR J0835-4510
show that the profile is made of four components that vary with frequency only
in their amplitude. The width and separation of the components remains fixed
and the spectral index of each component can be determined independently.
05/2011;
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S. Burke-Spolaor, M. Bailes,
S. Johnston,
S. D. Bates,
N. D. R. Bhat,
M. Burgay,
N. D'Amico,
A. Jameson,
M. J. Keith,
M Kramer,
L. Levin,
S. Milia,
A. Possenti,
B. Stappers,
W. van Straten
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ABSTRACT: We present the search methods and initial results for transient radio signals
in the High Time Resolution Universe (HTRU) Survey. The HTRU survey's
single-pulse search, the software designed to perform the search, and a
determination of the HTRU survey's sensitivity to single pulses are described.
Initial processing of a small fraction of the survey has produced 11
discoveries, all of which are sparsely-emitting neutron stars, as well as
provided confirmation of two previously unconfirmed neutron stars. Most of the
newly discovered objects lie in regions surveyed previously, indicating both
the improved sensitivity of the HTRU survey observing system and the dynamic
nature of the radio sky. The cycles of active and null states in nulling
pulsars, rotating radio transients (RRATs), and long-term intermittent pulsars
are explored in the context of determining the relationship between these
populations, and of the sensitivity of a search to the various
radio-intermittent neutron star populations. This analysis supports the case
that many RRATs are in fact high-null-fraction pulsars (i. e. with null
fraction >~0.95), and indicates that intermittent pulsars appear distinct from
nulling pulsars in their activity cycle timescales. We find that in the
measured population, there is a deficit of pulsars with typical emission
timescales greater than ~300 s that is not readily explained by selection
effects. The HTRU low-latitude survey will be capable of addressing whether
this deficit is physical. We predict that the HTRU survey will explore pulsars
with a broad range of nulling fractions (up to and beyond 0.999), and at its
completion is likely to increase the currently known RRATs by a factor of more
than two.
02/2011;
