163 research outputs found
A multiwavlength study of PSR B0628-28: The first overluminous rotation-powered pulsar?
The ROSAT source RX J0630.8-2834 was suggested by positional coincidence to
be the X-ray counterpart of the old field pulsar PSR B0628-28. This
association, however, was regarded to be unlikely based on the computed
energetics of the putative X-ray counterpart. In this paper we report on
multiwavelength observations of PSR B0628-28 made with the ESO/NTT observatory
in La Silla, the Jodrell Bank radio observatory and XMM-Newton. Although the
optical observations do not detect any counterpart of RX J0630.8-2834 down to a
limiting magnitude of V=26.1 mag and B=26.3 mag, XMM-Newton observations
finally confirmed it to be the pulsar's X-ray counterpart by detecting X-ray
pulses with the radio pulsar's spin-period. The X-ray pulse profile is
characterized by a single broad peak with a second smaller peak leading the
main pulse component by ~144 degree. The fraction of pulsed photons is (38 +-
7)% with no strong energy dependence in the XMM-Newton bandpass. The pulsar's
X-ray spectrum is well described by a single component power law with photon
index 2.63^{+0.23}_{-0.15}, indicating that the pulsar's X radiation is
dominated by non-thermal emission processes. A low level contribution of
thermal emission from residual cooling or from heated polar caps, cannot be
excluded. The pulsar's spin-down to X-ray energy conversion efficiency is
obtained to be ~16% for the radio dispersion measure inferred pulsar distance.
If confirmed, PSR B0628-28 would be the first X-ray overluminous
rotation-powered pulsar identified among all ~1400 radio pulsars known today.Comment: Accepted for publication in ApJ. Find a paper copy with higher
resolution images at
ftp://ftp.xray.mpe.mpg.de/people/web/astro-ph-0505488_rev2.pd
Polarized radio emission from a magnetar
We present polarization observations of the radio emitting magnetar AXP
J1810-197. Using simultaneous multi-frequency observations performed at 1.4,
4.9 and 8.4 GHz, we obtained polarization information for single pulses and the
average pulse profile at several epochs. We find that in several respects this
magnetar source shows similarities to the emission properties of normal radio
pulsars while simultaneously showing striking differences. The emission is
nearly 80-95% polarized, often with a low but significant degree of circular
polarization at all frequencies which can be much greater in selected single
pulses. The position angle swing has a low average slope of only 1 deg/deg,
deviating significantly from an S-like swing as often seen in radio pulsars
which is usually interpreted in terms of a rotating vector model and a dipolar
magnetic field. The observed position angle is consistent at all frequencies
while showing significant secular variations. On average the interpulse is less
linearly polarized but shows a higher degree of circular polarization. Some
epochs reveal the existence of non-orthogonal emission modes in the main pulse
and systematic wiggles in the PA swing, while the interpulse shows a large
variety of position angle values. We interprete many of the emission properties
as propagation effects in a non-dipolar magnetic field configuration where
emission from different multipole components is observed.Comment: accepted for publication in MNRAS, 15 pages, 11 figures. Figure 9 in
reduced quality, full resolution preprint at
ftp://ftp.jb.man.ac.uk/pub/mk/preprint/ksj+07.pdf, typos fixe
Precision timing of PSR J1012+5307 and strong-field GR tests
We report on the high precision timing analysis of the pulsar-white dwarf
binary PSR J1012+5307. Using 15 years of multi-telescope data from the European
Pulsar Timing Array (EPTA) network, a significant measurement of the variation
of the orbital period is obtained. Using this ideal strong-field gravity
laboratory we derive theory independent limits for both the dipole radiation
and the variation of the gravitational constant.Comment: 3 pages, Proceedings of the 12th Marcel Grossmann Meeting on General
Relativity (MG 12
The Geometry of PSR B0031-07
PSR B0031-07 is well known to exhibit three different modes of drifting
sub-pulses (mode A, B and C). It has recently been shown that in a
multifrequency observation, consisting of 2700 pulses, all driftmodes were
visible at low frequencies, while at 4.85 GHz only mode-A drift or non-drifting
emission was detected. This suggests that modes A and B are emitted in
sub-beams, rotating at a fixed distance from the magnetic axis, with the mode-B
sub-beams being closer to the magnetic axis than the mode-A sub-beams. Diffuse
emission between the sub-beams can account for the non-drifting emission. Using
the results of an analysis of simultaneous multifrequency observations of PSR
B0031-07, we set out to construct a geometrical model that includes emission
from both sub-beams and diffuse emission and describes the regions of the radio
emission of PSR B0031-07 at each emission frequency for driftmodes A and B.
Based on the vertical spacing between driftbands, we have determined the
driftmode of each sequence of drift. To restrict the model, we calculated
average polarisation and intensity characteristics for each driftmode and at
each frequency. The model reproduces the observed polarisation and intensity
characteristics, suggesting that diffuse emission plays an important role in
the emission properties of PSR B0031-07. The model further suggests that the
emission heights of this pulsar range from a few kilometers to a little over 10
kilometers above the pulsar surface. We also find that the relationships
between height and frequency of emission that follow from curvature radiation
and from plasma-frequency emission could not be used to reproduce the observed
frequency dependence of the width of the average intensity profiles.Comment: 15 pages, 9 figures, 8 tables, accepted for publication in A&
Radio emission from a pulsarâs magnetic pole revealed by general relativity
International audienceBinary pulsars are affected by general relativity (GR), causing the spin axis of each pulsar to precess. We present polarimetric radio observations of the pulsar PSR J1906+0746 that demonstrate the validity of the geometrical model of pulsar polarization. We reconstruct the (sky-projected) polarization emission map over the pulsarâs magnetic pole and predict the disappearance of the detectable emission by 2028. Two tests of GR are performed using this system, including the spin precession for strongly self-gravitating bodies. We constrain the relativistic treatment of the pulsar polarization model and measure the pulsar beaming fraction, with implications for the population of neutron stars and the expected rate of neutron star mergers
Multi-telescope timing of PSR J1518+4904
PSR J1518+4904 is one of only 9 known double neutron star systems. These
systems are highly valuable for measuring the masses of neutron stars,
measuring the effects of gravity, and testing gravitational theories. We
determine an improved timing solution for a mildly relativistic double neutron
star system, combining data from multiple telescopes. We set better constraints
on relativistic parameters and the separate masses of the system, and discuss
the evolution of PSR J1518+4904 in the context of other double neutron star
systems. PSR J1518+4904 has been regularly observed for more than 10 years by
the European Pulsar Timing Array (EPTA) network using the Westerbork, Jodrell
Bank, Effelsberg and Nancay radio telescopes. The data were analysed using the
updated timing software Tempo2. We have improved the timing solution for this
double neutron star system. The periastron advance has been refined and a
significant detection of proper motion is presented. It is not likely that more
post-Keplerian parameters, with which the individual neutron star masses and
the inclination angle of the system can be determined separately, can be
measured in the near future. Using a combination of the high-quality data sets
present in the EPTA collaboration, extended with the original GBT data, we have
constrained the masses in the system to m_p1.55 msun (95.4%
confidence), and the inclination angle of the orbit to be less than 47 degrees
(99%). From this we derive that the pulsar in this system possibly has one of
the lowest neutron star masses measured to date. From evolutionary
considerations it seems likely that the companion star, despite its high mass,
was formed in an electron-capture supernova.Comment: 11 pages, 8 figures, accepted by A&
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
Simultaneous multi-frequency single-pulse properties of AXP XTE J1810-197
We have used the 76-m Lovell, 94-m equivalent WSRT and 100-m Effelsberg radio
telescopes to investigate the simultaneous single-pulse properties of the radio
emitting magnetar AXP XTE J1810-197 at frequencies of 1.4, 4.8 and 8.35 GHz
during May and July 2006. We study the magnetar's pulse-energy distributions
which are found to be very peculiar as they are changing on time-scales of days
and cannot be fit by a single statistical model. The magnetar exhibits strong
spiky single giant-pulse-like subpulses, but they do not fit the definition of
the giant pulse or giant micropulse phenomena. Measurements of the
longitude-resolved modulation index reveal a high degree of intensity
fluctuations on day-to-day time-scales and dramatic changes across pulse phase.
We find the frequency evolution of the modulation index values differs
significantly from what is observed in normal radio pulsars. We find that no
regular drifting subpulse phenomenon is present at any of the observed
frequencies at any observing epoch. However, we find a quasi-periodicity of the
subpulses present in the majority of the observing sessions. A correlation
analysis indicates a relationship between components from different
frequencies. We discuss the results of our analysis in light of the emission
properties of normal radio pulsars and a recently proposed model which takes
radio emission from magnetars into consideration.Comment: 15 pages, 11 figures, accepted for publication by MNRA
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