362 research outputs found
Resolving discrete pulsar spin-down states with current and future instrumentation
An understanding of pulsar timing noise offers the potential to improve the
timing precision of a large number of pulsars as well as facilitating our
understanding of pulsar magnetospheres. For some sources, timing noise is
attributable to a pulsar switching between two different spin-down rates
. Such transitions may be common but difficult to resolve using
current techniques. In this work, we use simulations of -variable
pulsars to investigate the likelihood of resolving individual
transitions. We inject step-changes in the value of with a wide
range of amplitudes and switching timescales. We then attempt to redetect these
transitions using standard pulsar timing techniques. The pulse arrival-time
precision and the observing cadence are varied. Limits on
detectability based on the effects such transitions have on the timing
residuals are derived. With the typical cadences and timing precision of
current timing programs, we find we are insensitive to a large region of
parameter space which encompasses small, short timescale
switches. We find, where the rotation and emission states are correlated, that
using changes to the pulse shape to estimate transition epochs, can
improve detectability in certain scenarios. The effects of cadence on detectability are discussed and we make comparisons with a known
population of intermittent and mode-switching pulsars. We conclude that for
short timescale, small switches, cadence should not be compromised when new
generations of ultra-sensitive radio telescopes are online.Comment: 19 pages, 11 figure
Constraints on viewing geometries from radio observations of -ray-loud pulsars using a novel method
We present radio intensity and polarisation profiles of 28
-ray-detected pulsars with the aim of putting constraints on their
viewing geometries using data from the Parkes telescope. Constraints are formed
both from the goodness-of-fit of the position angles to the Rotating Vector
Model and from the beam opening angle considering aberration and retardation
effects. Uncertainties on the relevant parameters are systematically taken into
account in order to produce a more robust constraint, using a new approach.
Surprisingly, we find that the distribution of the magnetic inclination angle
() in this subset of pulsars peaks at low values, contrary to the
predictions of -ray models. We find a lack of correlation between these
and a set of values which were derived using -ray light
curves, suggesting a problem in the interpretation of the data in one or both
of these domains. Finally, we also show that the distribution of
pulsars with multiple radio components is no different to that of
single-component pulsars.Comment: 23 pages, 31 figures Submitted to MNRA
Long-term Observations of Three Nulling Pulsars
We present an analysis of approximately 200 hours of observations of the
pulsars J16345107, J17174054 and J18530505, taken over the course of
14.7 yr. We show that all of these objects exhibit long term nulls and
radio-emitting phases (i.e. minutes to many hours), as well as considerable
nulling fractions (NFs) in the range . PSR J17174054 is
also found to exhibit short timescale nulls () and burst phases
() during its radio-emitting phases. This behaviour acts to
modulate the NF, and therefore the detection rate of the source, over
timescales of minutes. Furthermore, PSR J18530505 is shown to exhibit a weak
emission state, in addition to its strong and null states, after sufficient
pulse integration. This further indicates that nulls may often only represent
transitions to weaker emission states which are below the sensitivity
thresholds of particular observing systems. In addition, we detected a
peak-to-peak variation of in the spin-down rate of PSR
J17174054, over timescales of hundreds of days. However, no long-term
correlation with emission variation was found.Comment: 10 pages, 8 figures, accepted for publication in MNRA
On the Apparent Nulls and Extreme Variability of PSR J1107-5907
We present an analysis of the emission behaviour of PSR J1107-5907, a source
known to exhibit separate modes of emission, using observations obtained over
approximately 10 yr. We find that the object exhibits two distinct modes of
emission; a strong mode with a broad profile and a weak mode with a narrow
profile. During the strong mode of emission, the pulsar typically radiates very
energetic emission over sequences of ~200-6000 pulses (~60 s-24 min), with
apparent nulls over time-scales of up to a few pulses at a time. Emission
during the weak mode is observed outside of these strong-mode sequences and
manifests as occasional bursts of up to a few clearly detectable pulses at a
time, as well as low-level underlying emission which is only detected through
profile integration. This implies that the previously described null mode may
in fact be representative of the bottom-end of the pulse intensity distribution
for the source. This is supported by the dramatic pulse-to-pulse intensity
modulation and rarity of exceptionally bright pulses observed during both modes
of emission. Coupled with the fact that the source could be interpreted as a
rotating radio transient (RRAT)-like object for the vast majority of the time,
if placed at a further distance, we advance that this object likely represents
a bridge between RRATs and extreme moding pulsars. Further to these emission
properties, we also show that the source is consistent with being a
near-aligned rotator and that it does not exhibit any measurable spin-down rate
variation. These results suggest that nulls observed in other intermittent
objects may in fact be representative of very weak emission without the need
for complete cessation. As such, we argue that longer (> 1 h) observations of
pulsars are required to discern their true modulation properties.Comment: 15 pages, 10 figures, accepted for publication in MNRA
The subpulse modulation properties of pulsars at 92 cm and the frequency dependence of subpulse modulation
A large sample of pulsars has been observed to study their subpulse
modulation at an observing wavelength (when achievable) of both 21 and 92 cm
using the Westerbork Synthesis Radio Telescope. In this paper we present the
92-cm data and a comparison is made with the already published 21-cm results.
We analysed 191 pulsars at 92 cm using fluctuation spectra. The sample of
pulsars is as unbiased as possible towards any particular pulsar
characteristics. For 15 pulsars drifting subpulses are discovered for the first
time and 26 of the new drifters found in the 21-cm data are confirmed. We
discovered nulling for 8 sources and 8 pulsars are found to intermittently emit
single pulses that have pulse energies similar to giant pulses. It is estimated
that at least half of the total population of pulsars have drifting subpulses
when observations with a high enough signal-to-noise ratio would be available.
It could well be that the drifting subpulse mechanism is an intrinsic property
of the emission mechanism itself, although for some pulsars it is difficult or
impossible to detect. Drifting subpulses are in general found at both
frequencies, although the chance of detecting drifting subpulses is possibly
slightly higher at 92 cm. It appears that the youngest pulsars have the most
disordered subpulses and the subpulses become more and more organized into
drifting subpulses as the pulsar ages. The correlations with the modulation
indices are argued to be consistent with the picture in which the radio
emission can be divided in a drifting subpulse signal plus a quasi-steady
signal which becomes, on average, stronger at high observing frequencies. The
measured values of P3 at the two frequencies are highly correlated, but there
is no evidence for a correlation with other pulsar parameters.Comment: 30 pages, 10 figures, accepted for publication in A&A, astro-ph
version is missing 191 figures due to file size restrictions. Please download
the appendix from
http://www.astron.nl/~stappers/wiki/doku.php?id=resources:publication
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