34 research outputs found
Gravitational radiation from pulsar glitches
The nonaxisymmetric Ekman flow excited inside a neutron star following a
rotational glitch is calculated analytically including stratification and
compressibility. For the largest glitches, the gravitational wave strain
produced by the hydrodynamic mass quadrupole moment approaches the sensitivity
range of advanced long-baseline interferometers. It is shown that the
viscosity, compressibility, and orientation of the star can be inferred in
principle from the width and amplitude ratios of the Fourier peaks (at the spin
frequency and its first harmonic) observed in the gravitational wave spectrum
in the plus and cross polarizations. These transport coefficients constrain the
equation of state of bulk nuclear matter, because they depend sensitively on
the degree of superfluidity.Comment: 28 page
Continuous-wave gravitational radiation from pulsar glitch recovery
Nonaxisymmetric, meridional circulation inside a neutron star, excited by a
glitch and persisting throughout the post-glitch relaxation phase, emits
gravitational radiation. Here, it is shown that the current quadrupole
contributes more strongly to the gravitational wave signal than the mass
quadrupole evaluated in previous work. We calculate the signal-to-noise ratio
for a coherent search and conclude that a large glitch may be detectable by
second-generation interferometers like the Laser Interferometer
Gravitational-Wave Observatory. It is shown that the viscosity and
compressibility of bulk nuclear matter, as well as the stratification
length-scale and inclination angle of the star, can be inferred from a
gravitational wave detection in principle.Comment: 19 pages, 4 figures, accepted for publication in MNRA
Gravitational-wave spin-down and stalling lower limits on the electrical resistivity of the accreted mountain in a millisecond pulsar
The electrical resistivity of the accreted mountain in a millisecond pulsar
is limited by the observed spin-down rate of binary radio millisecond pulsars
(BRMSPs) and the spins and X-ray fluxes of accreting millisecond pulsars
(AMSPs). We find (where is the
spin-down age) for BRMSPs and (where
and are the actual and Eddington
accretion rates) for AMSPs. These limits are inferred assuming that the
mountain attains a steady state, where matter diffuses resistively across
magnetic flux surfaces but is replenished at an equal rate by infalling
material. The mountain then relaxes further resistively after accretion ceases.
The BRMSP spin-down limit approaches the theoretical electron-impurity
resistivity at temperatures \ga 10^5 K for an impurity concentration of , while the AMSP stalling limit falls two orders of magnitude below the
theoretical electron-phonon resistivity for temperatures above K. Hence
BRMSP observations are already challenging theoretical resistivity calculations
in a useful way. Next-generation gravitational-wave interferometers will
constrain at a level that will be competitive with electromagnetic
observations.Comment: accepted for publication in ApJ
The effect of realistic equations of state and general relativity on the "snowplow" model for pulsar glitches
Many pulsars are observed to "glitch", i.e. show sudden jumps in their
rotational frequency , some of which can be as large as in a subset of pulsars known as giant
glitchers. Recently Pizzochero (2011) has shown that an analytic model based on
realistic values for the pinning forces in the crust and for the angular
momentum transfer in the star can describe the average properties of giant
glitches, such as the inter-glitch waiting time, the step in frequency and that
in frequency derivative. In this paper we extend the model (originally
developed in Newtonian gravity and for a polytropic equation of state) to
realistic backgrounds obtained by integrating the relativistic equations of
stellar structure and using physically motivated equations of state to describe
matter in the neutron star. We find that this more detailed treatment still
reproduces the main features of giant glitches in the Vela pulsar and allows us
to set constraints on the equation of state. In particular we find that stiffer
equations of state are favoured and that it is unlikely that the Vela pulsar
has a high mass (larger than ).Comment: 15 pages, 8 figures, submitted to MNRA
A study of 315 glitches in the rotation of 102 pulsars
The rotation of more than 700 pulsars has been monitored using the 76-m
Lovell Telescope at Jodrell Bank. Here we report on a new search for glitches
in the observations, revealing 128 new glitches in the rotation of 63 pulsars.
Combining these new data with those already published we present a database
containing 315 glitches in 102 pulsars. The database was used to study the
glitch activity among the pulsar population, finding that it peaks for pulsars
with a characteristic age tau_c ~ 10kyr and decreases for longer values of
tau_c, disappearing for objects with tau_c > 20Myr. The glitch activity is also
smaller in the very young pulsars (tau_c <~ 1kyr). The cumulative effect of
glitches, a collection of instantaneous spin up events, acts to reduce the
regular long term spindown rate |nudot| of the star. The percentage of |nudot|
reversed by glitch activity was found to vary between 0.5% and 1.6% for pulsars
with spindown rates |nudot| between 10^(-14) and 3.2*10^(-11) Hz/s, decreasing
to less than 0.01% at both higher and lower spindown rates. These ratios are
interpreted in terms of the amount of superfluid involved in the generation of
glitches. In this context the activity of the youngest pulsar studied, the Crab
pulsar, may be explained by quake-like activity within the crust. Pulsars with
low spindown rates seem to exhibit mostly small glitches, matching well the
decrease of their crustal superfluid.
Through the analysis of glitch sizes it was found that the particular
glitching behaviour of PSR J0537-6910 and the Vela pulsar may be shared by most
Vela-like pulsars. These objects present most of their glitches with
characteristic frequency and frequency derivative jumps, occurring at regular
intervals of time. Their behaviour is different from other glitching pulsars of
similar characteristic age.Comment: 26 pages, 17 figures, 6 tables. Accepted for publication in MNRA
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
The STRESS-NL database: A resource for human acute stress studies across the Netherlands
Stress initiates a cascade of (neuro)biological, physiological, and behavioral changes, allowing us to respond to a challenging environment. The human response to acute stress can be studied in detail in controlled settings, usually in a laboratory environment. To this end, many studies employ acute stress paradigms to probe stress-related outcomes in healthy and patient populations. Though valuable, these studies in themselves often have relatively limited sample sizes. We established a data-sharing and collaborative interdisciplinary initiative, the STRESS-NL database, which combines (neuro)biological, physiological, and behavioral data across many acute stress studies in order to accelerate our understanding of the human acute stress response in health and disease (www.stressdatabase.eu). Researchers in the stress field from 12 Dutch research groups of 6 Dutch universities created a database to achieve an accurate inventory of (neuro)biological, physiological, and behavioral data from laboratory-based human studies that used acute stress tests. Currently, the STRESS-NL database consists of information on 5529 individual participants (2281 females and 3348 males, age range 6-99 years, mean age 27.7 ± 16 years) stemming from 57 experiments described in 42 independent studies. Studies often did not use the same stress paradigm; outcomes were different and measured at different time points. All studies currently included in the database assessed cortisol levels before, during and after experimental stress, but cortisol measurement will not be a strict requirement for future study inclusion. Here, we report on the creation of the STRESS-NL database and infrastructure to illustrate the potential of accumulating and combining existing data to allow meta-analytical, proof-of-principle analyses. The STRESS-NL database creates a framework that enables human stress research to take new avenues in explorative and hypothesis-driven data analyses with high statistical power. Future steps could be to incorporate new studies beyond the borders of the Netherlands; or build similar databases for experimental stress studies in rodents. In our view, there are major scientific benefits in initiating and maintaining such international efforts
Modelling pulsar glitches with realistic pinning forces: a hydrodynamical approach
Although pulsars are one of the most stable clocks in the universe, many of
them are observed to 'glitch', i.e. to suddenly increase their spin frequency
(\nu) with fractional increases that range from \Delta\nu/\nu \approx 10^{-11}
to 10^{-5}. In this paper we focus on the 'giant' glitches, i.e. glitches with
fractional increases in the spin rate of the order of \Delta\nu/{\nu} \approx
10^{-6}, that are observed in a sub class of pulsars including the Vela. We
show that giant glitches can be modelled with a two-fluid hydrodynamical
approach. The model is based on the formalism for superfluid neutron stars of
Andersson and Comer (2006) and on the realistic pinning forces of Grill and
Pizzochero (2011). We show that all stages of Vela glitches, from the rise to
the post-glitch relaxation, can be reproduced with a set of physically
reasonable parameters and that the sizes and waiting times between giant
glitches in other pulsars are also consistent with our model.Comment: submitted to MNRA