-
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;
-
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;
-
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;
-
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;
-
F. R. Ferraro,
R. P. Mignani,
C. Pallanca,
E. Dalessandro,
B. Lanzoni,
A. Pellizzoni,
A. Possenti,
M. Burgay,
F. Camilo, N. D'Amico,
A. G. Lyne,
M. Kramer,
R. N. Manchester
[show abstract]
[hide abstract]
ABSTRACT: We present the first optical observations of the unique system J0737-3039
(composed of two pulsars, hereafter PSR-A and PSR-B). Ultra-deep optical
observations, performed with the High Resolution Camera of the Advanced Camera
for Surveys on board the Hubble Space Telescope could not detect any optical
emission from the system down to m_F435W=27.0 and m_F606W=28.3. The estimated
optical flux limits are used to constrain the three-component (two thermal and
one non-thermal) model recently proposed to reproduce the XMM-Newton X-ray
spectrum. They suggest the presence of a break at low energies in the
non-thermal power law component of PSR-A and are compatible with the expected
black-body emission from the PSR-B surface. The corresponding efficiency of the
optical emission from PSR-A's magnetosphere would be comparable to that of
other Myr-old pulsars, thus suggesting that this parameter may not dramatically
evolve over a time-scale of a few Myr.
02/2012;
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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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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;
-
R. van Haasteren,
Y. Levin,
G. H. Janssen,
K. Lazaridis,
M. Kramer B. W. Stappers,
G. Desvignes,
M. B. Purver,
A. G. Lyne,
R. D. Ferdman,
A. Jessner,
I. Cognard,
G. Theureau, N. D'Amico,
A. Possenti,
M. Burgay,
A. Corongiu,
J. W. T. Hessels,
R. Smits,
J. P. W. Verbiest
[show abstract]
[hide abstract]
ABSTRACT: Direct detection of low-frequency gravitational waves ($10^{-9} - 10^{-8}$
Hz) is the main goal of pulsar timing array (PTA) projects. One of the main
targets for the PTAs is to measure the stochastic background of gravitational
waves (GWB) whose characteristic strain is expected to approximately follow a
power-law of the form $h_c(f)=A (f/\hbox{yr}^{-1})^{\alpha}$, where $f$ is the
gravitational-wave frequency. In this paper we use the current data from the
European PTA to determine an upper limit on the GWB amplitude $A$ as a function
of the unknown spectral slope $\alpha$ with a Bayesian algorithm, by modelling
the GWB as a random Gaussian process. For the case $\alpha=-2/3$, which is
expected if the GWB is produced by supermassive black-hole binaries, we obtain
a 95% confidence upper limit on $A$ of $6\times 10^{-15}$, which is 1.8 times
lower than the 95% confidence GWB limit obtained by the Parkes PTA in 2006. Our
approach to the data analysis incorporates the multi-telescope nature of the
European PTA and thus can serve as a useful template for future
intercontinental PTA collaborations.
03/2011;
-
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 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;
-
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 5 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 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 Solar Masses. 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 makes 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.
01/2011;
-
C. Pallanca,
E. Dalessandro,
F. R. Ferraro,
B. Lanzoni,
R. T. Rood,
A. Possenti, N. D'Amico,
P. C. Freire,
I. Stairs,
S. M. Ransom,
S. Begin
[show abstract]
[hide abstract]
ABSTRACT: We report on the optical identification of the companion star to the eclipsing millisecond pulsar PSR J1824-2452H in the galactic globular cluster M28 (NGC 6626). This star is at only 0.2" from the nominal position of the pulsar and it shows optical variability (~ 0.25 mag) that nicely correlates with the pulsar orbital period. It is located on the blue side of the cluster main sequence, ~1.5 mag fainter than the turn-off point. The observed light curve shows two distinct and asymmetric minima, suggesting that the companion star is suffering tidal distortion from the pulsar. This discovery increases the number of non-degenerate MSP companions optically identified so far in globular clusters (4 out of 7), suggesting that these systems could be a common outcome of the pulsar recycling process, at least in dense environments where they can be originated by exchange interactions. Comment: accepted for publication on ApJ, 17 pages, 5 figures
10/2010;
-
M. Pilia,
A. Pellizzoni,
A. Trois,
F. Verrecchia,
P. Esposito,
P. Weltevrede,
S. Johnston,
M. Burgay,
A. Possenti,
E. Del Monte, [......],
E Vallazza,
S. Vercellone,
V. Vittorini,
A. Zambra,
D. Zanello,
C. Pittori,
F. Lucarelli,
P. Giommi,
L. Salotti,
G. F. Bignami
[show abstract]
[hide abstract]
ABSTRACT: We present the results of new Agile observations of PSR B1509-58 performed over a period of 2.5 years following the detection obtained with a subset of the present data. The modulation significance of the lightcurve above 30 MeV is at a 5$\sigma$ confidence level and the lightcurve is similar to those found earlier by Comptel up to 30 MeV: a broad asymmetric first peak reaching its maximum 0.39 +/- 0.02 cycles after the radio peak plus a second peak at 0.94 +/- 0.03. The gamma-ray spectral energy distribution of the pulsed flux detected by Comptel and Agile is well described by a power-law (photon index alpha=1.87+/-0.09) with a remarkable cutoff at E_c=81 +/- 20 MeV, representing the softest spectrum observed among gamma-ray pulsars so far. The pulsar luminosity at E > 1 MeV is $L_{\gamma}=4.2^{+0.5}_{-0.2} \times10^{35}$ erg/s, assuming a distance of 5.2 kpc, which implies a spin-down conversion efficiency to gamma-rays of $\sim 0.03$. The unusual soft break in the spectrum of PSR B1509-58 has been interpreted in the framework of polar cap models as a signature of the exotic photon splitting process in the strong magnetic field of this pulsar. In this interpretation our spectrum constrains the magnetic altitude of the emission point(s) at 3 km above the neutron star surface, implying that the attenuation may not be as strong as formerly suggested because pair production can substitute photon splitting in regions of the magnetosphere where the magnetic field becomes too low to sustain photon splitting. In the case of an outer-gap scenario, or the two pole caustic model, better constraints on the geometry of the emission would be needed from the radio band in order to establish whether the conditions required by the models to reproduce Agile lightcurves and spectra match the polarization measurements. Comment: 17 pages, 2 figures, accepted for publication in ApJ
08/2010;
-
M. J. Keith,
A. Jameson,
W. van Straten,
M. Bailes,
S. Johnston,
M Kramer,
A. Possenti,
S. D. Bates,
N. D. R. Bhat,
M. Burgay,
S. Burke-Spolaor, N. D'Amico,
L. Levin,
P. L. McMahon,
S. Milia,
B. W. Stappers
[show abstract]
[hide abstract]
ABSTRACT: We have embarked on a survey for pulsars and fast transients using the 13-beam Multibeam receiver on the Parkes radio telescope. Installation of a digital backend allows us to record 400 MHz of bandwidth for each beam, split into 1024 channels and sampled every 64 us. Limits of the receiver package restrict us to a 340 MHz observing band centred at 1352 MHz. The factor of eight improvement in frequency resolution over previous multibeam surveys allows us to probe deeper into the Galactic plane for short duration signals such as the pulses from millisecond pulsars. We plan to survey the entire southern sky in 42641 pointings, split into low, mid and high Galactic latitude regions, with integration times of 4200, 540 and 270 s respectively. Simulations suggest that we will discover 400 pulsars, of which 75 will be millisecond pulsars. With ~30% of the mid-latitude survey complete, we have re-detected 223 previously known pulsars and discovered 27 pulsars, 5 of which are millisecond pulsars. The newly discovered millisecond pulsars tend to have larger dispersion measures than those discovered in previous surveys, as expected from the improved time and frequency resolution of our instrument. Comment: Updated author list. 10 pages, 7 figures. For publication in MNRAS
Monthly Notices of the Royal Astronomical Society 06/2010; · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present results of near-infrared spectroscopy of the late-type star coincident with the young pulsar PSR J1740−3052. High-spectral-resolution K-band (∼2.2 μm) observations were obtained in 2003 with the Infrared Spectrometer and Array Camera instrument on the Very Large Telescope and with Phoenix on the Gemini Telescope. We find no consistent evidence of a radial velocity shift in the star compatible with the known pulsar orbit, setting a limit on the minimum mass of the star, if it is the companion, of 60 M⊙. We therefore conclude that the observed star is likely to be a foreground object. No sign of the previously reported Brackett-γ emission was found in this analysis. Our findings support previous suggestions that the companion to PSR J1740−3052 is most likely a massive B-type star that has been obscured by the bright late-type star in the foreground.
Monthly Notices of the Royal Astronomical Society 06/2010; 406(3):1848 - 1852. · 4.90 Impact Factor
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R D Ferdman,
R van Haasteren,
C G Bassa,
M Burgay,
I Cognard,
A Corongiu, N D'Amico,
G Desvignes,
J W T Hessels,
G H Janssen, [......],
K Lazaridis,
Y Levin,
A G Lyne,
M Pilia,
A Possenti,
M Purver,
B Stappers,
S Sanidas,
R Smits,
G Theureau
[show abstract]
[hide abstract]
ABSTRACT: The European Pulsar Timing Array (EPTA) is a multi-institutional, multi-telescope collaboration, with the goal of using high-precision pulsar timing to directly detect gravitational waves. In this paper we discuss the EPTA member telescopes, current achieved timing precision and near-future goals. We report a preliminary upper limit to the amplitude of a gravitational wave background. We also discuss the Large European Array for Pulsars, in which the five major European telescopes involved in pulsar timing will be combined to provide a coherent array that will give similar sensitivity to the Arecibo radio telescope, and larger sky coverage.
Classical and Quantum Gravity 04/2010; 27(8):084014. · 3.32 Impact Factor
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B. P. Abbott,
R. Abbott,
F. Acernese,
R. Adhikari,
P. Ajith,
B. Allen,
G. Allen,
M. Alshourbagy,
R. S. Amin,
S. B. Anderson, [......],
G. B. Hobbs,
M. Kramer,
A. G. Lyne,
R. N. Manchester,
F. E. Marshall,
J. Middleditch,
A. Possenti,
S. M. Ransom,
I. H. Stairs,
and B. Stappers
[show abstract]
[hide abstract]
ABSTRACT: We present a search for gravitational waves from 116 known millisecond and young pulsars using data from the fifth science run of the LIGO detectors. For this search, ephemerides overlapping the run period were obtained for all pulsars using radio and X-ray observations. We demonstrate an updated search method that allows for small uncertainties in the pulsar phase parameters to be included in the search. We report no signal detection from any of the targets and therefore interpret our results as upper limits on the gravitational wave signal strength. The most interesting limits are those for young pulsars. We present updated limits on gravitational radiation from the Crab pulsar, where the measured limit is now a factor of 7 below the spin-down limit. This limits the power radiated via gravitational waves to be less than ~2% of the available spin-down power. For the X-ray pulsar J0537 – 6910 we reach the spin-down limit under the assumption that any gravitational wave signal from it stays phase locked to the X-ray pulses over timing glitches, and for pulsars J1913+1011 and J1952+3252 we are only a factor of a few above the spin-down limit. Of the recycled millisecond pulsars, several of the measured upper limits are only about an order of magnitude above their spin-down limits. For these our best (lowest) upper limit on gravitational wave amplitude is 2.3 × 10–26 for J1603 – 7202 and our best (lowest) limit on the inferred pulsar ellipticity is 7.0 × 10–8 for J2124 – 3358.
The Astrophysical Journal 03/2010; 713(1):671. · 6.02 Impact Factor
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A Pellizzoni,
A Trois,
M Tavani,
M Pilia,
A Giuliani,
G Pucella,
P Esposito,
S Sabatini,
G Piano,
A Argan, [......],
F Verrecchia,
V Vittorini,
A Zambra,
D Zanello,
P Giommi,
S Colafrancesco,
A Antonelli,
L Salotti, N D'Amico,
G F Bignami
[show abstract]
[hide abstract]
ABSTRACT: Pulsars are known to power winds of relativistic particles that can produce bright nebulae by interacting with the surrounding medium. These pulsar wind nebulae are observed by their radio, optical, and x-ray emissions, and in some cases also at TeV (teraelectron volt) energies, but the lack of information in the gamma-ray band precludes drawing a comprehensive multiwavelength picture of their phenomenology and emission mechanisms. Using data from the AGILE satellite, we detected the Vela pulsar wind nebula in the energy range from 100 MeV to 3 GeV. This result constrains the particle population responsible for the GeV emission and establishes a class of gamma-ray emitters that could account for a fraction of the unidentified galactic gamma-ray sources.
Science 02/2010; 327(5966):663-5. · 31.20 Impact Factor
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The LIGO Scientific Collaboration,
The Virgo Collaboration,
B. P. Abbott,
R. Abbott,
F. Acernese,
R. Adhikari,
P. Ajith,
B. Allen,
G. Allen,
M. Alshourbagy, [......],
G. B. Hobbs,
M. Kramer,
A. G. Lyne,
R. N. Manchester,
F. E. Marshall,
J. Middleditch,
A. Possenti,
S. M. Ransom,
I. H. Stairs,
B. Stappers
[show abstract]
[hide abstract]
ABSTRACT: We present a search for gravitational waves from 116 known millisecond and
young pulsars using data from the fifth science run of the LIGO detectors. For
this search ephemerides overlapping the run period were obtained for all
pulsars using radio and X-ray observations. We demonstrate an updated search
method that allows for small uncertainties in the pulsar phase parameters to be
included in the search. We report no signal detection from any of the targets
and therefore interpret our results as upper limits on the gravitational wave
signal strength. The most interesting limits are those for young pulsars. We
present updated limits on gravitational radiation from the Crab pulsar, where
the measured limit is now a factor of seven below the spin-down limit. This
limits the power radiated via gravitational waves to be less than ~2% of the
available spin-down power. For the X-ray pulsar J0537-6910 we reach the
spin-down limit under the assumption that any gravitational wave signal from it
stays phase locked to the X-ray pulses over timing glitches, and for pulsars
J1913+1011 and J1952+3252 we are only a factor of a few above the spin-down
limit. Of the recycled millisecond pulsars several of the measured upper limits
are only about an order of magnitude above their spin-down limits. For these
our best (lowest) upper limit on gravitational wave amplitude is 2.3x10^-26 for
J1603-7202 and our best (lowest) limit on the inferred pulsar ellipticity is
7.0x10^-8 for J2124-3358.
09/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: The timing of radio pulsars provides a tool for studying a wide range of fundamental physical and astrophysical problems. The best results are obtained by regular, frequent timing observations of a large number of sources at various frequencies. We describe a project which aims to improve on all of the above parameters by combining timing data from the pulsar timing programs of 4 European groups to form the so-called EPTA. These data will be used to study, amongst other things, relativistic binaries and gravitational waves.
Chinese Journal of Astronomy and Astrophysics 04/2009; 6(S2):298. · 0.89 Impact Factor
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J. van Leeuwen,
J. M. Cordes,
D. R. Lorimer,
P. C. C. Freire,
F. Camilo,
I. H. Stairs,
D. J. Nice,
D. J. Champion,
R. Ramachandran,
A. J. Faulkner, [......],
F. Crawford,
A. N. Lommen,
D. C. Backer,
M. Kramer,
B. W. Stappers,
G. B. Hobbs,
A. Possenti, N. D'Amico,
C.-A. Faucher-Giguère,
M. Burgay
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ABSTRACT: The recently started Arecibo L-band Feed Array (ALFA) pulsar survey aims to find ~1000 new pulsars. Due to its high time and frequency resolution the survey is especially sensitive to millisecond pulsars, which have the potential to test gravitational theories, detect gravitational waves and probe the neutron-star equation of state. Here we report the results of our preliminary analysis: in the first months we have discovered 21 new pulsars. One of these, PSR J1906+0746, is a young 144-ms pulsar in a highly relativistic 3.98-hr low-eccentricity orbit. The 2.61±0.02 M system is expected to coalesce in ~300 Myr and contributes significantly to the computed cosmic inspiral rate of compact binary systems.
Chinese Journal of Astronomy and Astrophysics 04/2009; 6(S2):311. · 0.89 Impact Factor
