177 research outputs found
Long term monitoring of mode switching for PSR B0329+54
The mode switching phenomenon of PSR B0329+54 is investigated based on the
long-term monitoring from September 2003 to April 2009 made with the Urumqi 25m
radio telescope at 1540 MHz. At that frequency, the change of relative
intensity between the leading and trailing components is the predominant
feature of mode switching. The intensity ratios between the leading and
trailing components are measured for the individual profiles averaged over a
few minutes. It is found that the ratios follow normal distributions, where the
abnormal mode has a wider typical width than the normal mode, indicating that
the abnormal mode is less stable than the normal mode. Our data show that 84.9%
of the time for PSR B0329+54 was in the normal mode and 15.1% was in the
abnormal mode. From the two passages of eight-day quasi-continuous observations
in 2004, and supplemented by the daily data observed with 15 m telescope at 610
MHz at Jodrell Bank Observatory, the intrinsic distributions of mode timescales
are constrained with the Bayesian inference method. It is found that the gamma
distribution with the shape parameter slightly smaller than 1 is favored over
the normal, lognormal and Pareto distributions. The optimal scale parameters of
the gamma distribution is 31.5 minutes for the abnormal mode and 154 minutes
for the normal mode. The shape parameters have very similar values, i.e.
0.75^{+0.22}_{-0.17} for the normal mode and 0.84^{+0.28}_{-0.22} for the
abnormal mode, indicating the physical mechanisms in both modes may be the
same. No long-term modulation of the relative intensity ratios was found for
both the modes, suggesting that the mode switching was stable. The intrinsic
timescale distributions, for the first time constrained for this pulsar,
provide valuable information to understand the physics of mode switching.Comment: 31 pages,12 figures, Accepted by the Ap
A flexible format for exchanging pulsar data
We describe a data format currently in use amongst European institutions for exchanging and archiving pulsar data. The format is designed to be as flexible as possible with regard to present and future compatibility with different operating systems. One application of the common format is simultaneous multi-frequency observations of single pulses. A data archive containing over 2500 pulse profiles stored in this format is now available via the Internet (see http://www.mpifr-bonn.mpg.de/pulsar/data), together with a small suite of computer programs that can read, write and display the data
Predicting language learners' grades in the L1, L2, L3 and L4: the effect of some psychological and sociocognitive variables
This study of 89 Flemish high-school students' grades for L1 (Dutch), L2 (French), L3 (English) and L4 (German) investigates the effects of three higher-level personality dimensions (psychoticism, extraversion, neuroticism), one lower-level personality dimension (foreign language anxiety) and sociobiographical variables (gender, social class) on the participants' language grades. Analyses of variance revealed no significant effects of the higher-level personality dimensions on grades. Participants with high levels of foreign language anxiety obtained significantly lower grades in the L2 and L3. Gender and social class had no effect. Strong positive correlations between grades in the different languages could point to an underlying sociocognitive dimension. The implications of these findings are discussed
Placing limits on the stochastic gravitational-wave background using European Pulsar Timing Array data
Direct detection of low-frequency gravitational waves (
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 , where 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 as a function
of the unknown spectral slope with a Bayesian algorithm, by modelling
the GWB as a random Gaussian process. For the case , which is
expected if the GWB is produced by supermassive black-hole binaries, we obtain
a 95% confidence upper limit on of , 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.Comment: 14 pages, 8 figures, 3 tables, mnras accepte
The characteristics of millisecond pulsar emission: I. Spectra, pulse shapes and the beaming fraction
We have monitored a large sample of millisecond pulsars using the 100-m
Effelsberg radio telescope in order to compare their radio emission properties
to the slowly rotating population. With some notable exceptions, our findings
suggest that the two groups of objects share many common properties. A
comparison of the spectral indices between samples of normal and millisecond
pulsars demonstrates that millisecond pulsar spectra are not significantly
different from those of normal pulsars. There is evidence, however, that
millisecond pulsars are slightly less luminous and less efficient radio
emitters compared to normal pulsars. We confirm recent suggestions that a
diversity exists among the luminosities of millisecond pulsars with the
isolated millisecond pulsars being less luminous than the binary millisecond
pulsars. There are indications that old millisecond pulsars exhibit somewhat
flatter spectra than the presumably younger ones. We present evidence that
millisecond pulsar profiles are only marginally more complex than those found
among the normal pulsar population. Moreover, the development of the profiles
with frequency is rather slow, suggesting very compact magnetospheres. The
profile development seems to anti-correlate with the companion mass and the
spin period, again suggesting that the amount of mass transfer in a binary
system might directly influence the emission properties. The angular radius of
radio beams of millisecond pulsars does not follow the scaling predicted from a
canonical pulsar model which is applicable for normal pulsars. Instead they are
systematically smaller. The smaller inferred luminosity and narrower emission
beams will need to be considered in future calculations of the birth-rate of
the Galactic population.Comment: 40 pages, 14 figures, accepted for publication in Ap
Generic tests of the existence of the gravitational dipole radiation and the variation of the gravitational constant
We present results from the high precision timing analysis of the
pulsar-white dwarf (WD) binary PSR J1012+5307 using 15 years of multi-telescope
data. Observations were performed regularly by the European Pulsar Timing Array
(EPTA) network, consisting of Effelsberg, Jodrell Bank, Westerbork and
Nan\c{c}ay. All the timing parameters have been improved from the previously
published values, most by an order of magnitude. In addition, a parallax
measurement of mas is obtained for the first time for PSR
J1012+5307, being consistent with the optical estimation from the WD companion.
Combining improved 3D velocity information and models for the Galactic
potential the complete evolutionary Galactic path of the system is obtained. A
new intrinsic eccentricity upper limit of is acquired,
one of the smallest calculated for a binary system and a measurement of the
variation of the projected semi-major axis also constrains the system's orbital
orientation for the first time. It is shown that PSR J1012+5307 is an ideal
laboratory for testing alternative theories of gravity. The measurement of the
change of the orbital period of the system of is used to set an upper limit on the dipole gravitational wave
emission that is valid for a wide class of alternative theories of gravity.
Moreover, it is shown that in combination with other binary pulsars PSR
J1012+5307 is an ideal system to provide self-consistent, generic limits, based
only on millisecond pulsar data, for the dipole radiation and the variation of
the gravitational constant .Comment: accepted for publication in MNRAS, 11 pages, 5 figures, 2 table
Revealing the X-ray emission processes of old rotation-powered pulsars: XMM-Newton Observations of PSR B0950+08,PSR B0823+26 and PSR J2043+2740
We have completed part of a program to study the X-ray emission properties of
old rotation-powered pulsars with XMM-Newton in order to probe and identify the
origin of their X-radiation. The X-ray emission from these old pulsars is
largely dominated by non-thermal processes. None of the observed spectra
required adding a thermal component consisting of either a hot polar cap or
surface cooling emission to model the data. The X-ray spectrum of PSR 0950+08
is best described by a single power law of photon-index
1.93^{+0.14}_{-0.12}.Taking optical data from the VLT FORS1 into account a
broken power law model is found to describe the pulsar's broadband spectrum
from the optical to the X-ray band. Temperature upper limits for possible
contributions from a heated polar cap or the whole neutron star surface are
T_{pc} < 0.87 x10^6 K and T_s < 0.48 x 10^6 K, respectively. We also find that
the X-ray emission from PSR 0950+08 is pulsed with two peaks per rotation
period. The phase separation between the two X-ray peaks is ~144 degree. The
main radio peak and the trailing X-ray peak are almost phase aligned. The
fraction of X-ray pulsed photons is ~30%. A phase-resolved spectral analysis
confirms the non-thermal nature of the pulsed emission. Detailed pulse profile
simulations constrain the pulsar's emission geometry to be that of an almost
orthogonal rotator. The spectral emission properties observed for PSR 0823+26
are similar to those of PSR 0950+08. For PSR J2043+2740 we report the first
detection of X-ray emission. A power law spectrum, or a combination of a
thermal and a power law spectrum all yield acceptable descriptions of its X-ray
spectrum. No X-ray pulses are detected from PSR J2043+2740. A pulsed fraction
upper limit is 57%.Comment: Accepted for publication in ApJ on July 15, 2004. The paper with
higher resolution images can be obtained form
ftp://ftp.xray.mpe.mpg.de/people/web/X-ray-emission-from-old-pulsar
The international pulsar timing array project: using pulsars as a gravitational wave detector
The International Pulsar Timing Array project combines observations of
pulsars from both Northern and Southern hemisphere observatories with the main
aim of detecting ultra-low frequency (~10^-9 to 10^-8 Hz) gravitational waves.
Here we introduce the project, review the methods used to search for
gravitational waves emitted from coalescing supermassive binary black-hole
systems in the centres of merging galaxies and discuss the status of the
project.Comment: accepted by Classical and Quantum Gravity. Review talk for the
Amaldi8 conference serie
The binary pulsar PSR J1811-1736: evidence of a low amplitude supernova kick
Aims: The binary pulsar PSR J1811-1736 has been identified, since its
discovery, as a member of a double neutron star system. Observations of such
binary pulsars allow the measurement of general relativistic effects, which in
turn lead to information about the orbiting objects and, in a few cases, to
tests of theories of gravity. Methods: Regular timing observations have been
carried out with three of the largest European radio telescopes involved in
pulsar research. The prospects of continued observations were studied with
simulated timing data. Pulse scattering times were measured using dedicated
observations at 1.4 GHz and at 3.1 GHz, and the corresponding spectral index
has also been determined. The possibility of detecting the yet unseen companion
as a radio pulsar was also investigated. A study of the natal kick received by
the younger neutron star at birth was performed. Results: We present an up to
date and improved timing solution for the binary pulsar PSR J1811-1736. One
post-Keplerian parameter, the relativistic periastron advance, is measured and
leads to the determination of the total mass of this binary system. The pulse
profile at 1.4 GHz is heavily broadened by interstellar scattering, limiting
the timing precision achievable at this frequency and the measurability of
other post-keplerian parameters. Interstellar scattering is unlikely to be the
reason for the continued failure to detect radio pulsations from the companion
of PSR J1811-1736. The probability distribution that we derive for the
amplitude of the kick imparted on the companion neutron star at its birth
indicates that the kick has been of low amplitude.Comment: 8 pages, 4 figures, accepted for publication on A&A. (Abridged
abstract
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