2,161 research outputs found
Assessing the Role of Spin Noise in the Precision Timing of Millisecond Pulsars
We investigate rotational spin noise (referred to as timing noise) in
non-accreting pulsars: millisecond pulsars, canonical pulsars, and magnetars.
Particular attention is placed on quantifying the strength and non-stationarity
of timing noise in millisecond pulsars because the long-term stability of these
objects is required to detect nanohertz gravitational radiation. We show that a
single scaling law is sufficient to characterize timing noise in millisecond
and canonical pulsars while the same scaling law underestimates the levels of
timing noise in magnetars. The scaling law, along with a detailed study of the
millisecond pulsar B1937+21, leads us to conclude that timing noise is latent
in most millisecond pulsars and will be measurable in many objects when better
arrival time estimates are obtained over long data spans. The sensitivity of a
pulsar timing array to gravitational radiation is strongly affected by any
timing noise. We conclude that detection of proposed gravitational wave
backgrounds will require the analysis of more objects than previously suggested
over data spans that depend on the spectra of both the gravitational wave
background and of the timing noise. It is imperative to find additional
millisecond pulsars in current and future surveys in order to reduce the
effects of timing noise.Comment: 16 pages and 6 figures. ApJ, accepte
Pulsar timing noise and the minimum observation time to detect gravitational waves with pulsar timing arrays
The sensitivity of pulsar timing arrays to gravitational waves is, at some
level, limited by timing noise. Red timing noise - the stochastic wandering of
pulse arrival times with a red spectrum - is prevalent in slow-spinning pulsars
and has been identified in many millisecond pulsars. Phenomenological models of
timing noise, such as from superfluid turbulence, suggest that the timing noise
spectrum plateaus below some critical frequency, , potentially aiding the
hunt for gravitational waves. We examine this effect for individual pulsars by
calculating minimum observation times, , over which the
gravitational wave signal becomes larger than the timing noise plateau. We do
this in two ways: 1) in a model-independent manner, and 2) by using the
superfluid turbulence model for timing noise as an example to illustrate how
neutron star parameters can be constrained. We show that the superfluid
turbulence model can reproduce the data qualitatively from a number of pulsars
observed as part of the Parkes Pulsar Timing Array. We further show how a value
of , derived either through observations or theory, can be related to
. This provides a diagnostic whereby the usefulness of timing
array pulsars for gravitational-wave detection can be quantified.Comment: Accepted for publication in MNRA
Red Noise in Anomalous X-ray Pulsar Timing Residuals
Anomalous X-ray Pulsars (AXPs), thought to be magnetars, exhibit poorly
understood deviations from a simple spin-down called "timing noise". AXP timing
noise has strong low-frequency components which pose significant challenges for
quantification. We describe a procedure for extracting two quantities of
interest, the intensity and power spectral index of timing noise. We apply this
procedure to timing data from three sources: a monitoring campaign of five
AXPs, observations of five young pulsars, and the stable rotator PSR B1937+21.Comment: submitted to the proceedings of the "40 Years of Pulsars" conferenc
An alternative interpretation of the timing noise in accreting millisecond pulsars
The measurement of the spin frequency in accreting millisecond X-ray pulsars
(AMXPs) is strongly affected by the presence of an unmodeled component in the
pulse arrival times called 'timing noise'. We show that it is possible to
attribute much of this timing noise to a pulse phase offset that varies in
correlation with X-ray flux, such that noise in flux translates into timing
noise. This could explain many of the pulse frequency variations previously
interpreted in terms of true spin up or spin down, and would bias measured spin
frequencies. Spin frequencies improved under this hypothesis are reported for
six AMXPs. The effect would most easily be accounted for by an accretion rate
dependent hot spot location.Comment: Submitted to ApJ Letter
Timing Noise in SGR 1806-20
We have phase connected a sequence of RXTE PCA observations of SGR 1806-20
covering 178 days. We find a simple secular spin-down model does not adequately
fit the data. The period derivative varies gradually during the observations
between 8.1 and 11.7 * 10^-11 s/s (at its highest, ~40% larger than the long
term trend), while the average burst rate as seen with BATSE drops throughout
the time interval. The phase residuals give no compelling evidence for
periodicity, but more closely resemble timing noise as seen in radio pulsars.
The magnitude of the timing noise, however, is large relative to the noise
level typically found in radio pulsars. Combining these results with the noise
levels measured for some AXPs, we find all magnetar candidates have \Delta_8
values larger than those expected from a simple extrapolation of the
correlation found in radio pulsars. We find that the timing noise in SGR
1806-20 is greater than or equal to the levels found in some accreting systems
(e.g., Vela X-1, 4U 1538-52 and 4U 1626-67), but the spin-down of SGR 1806-20
has thus far maintained coherence over 6 years. Alternatively, an orbital model
with a period P_orb = 733 days provides a statistically acceptable fit to the
data. If the phase residuals are created by Doppler shifts from a
gravitationally bound companion, then the allowed parameter space for the mass
function (small) and orbital separation (large) rule out the possibility of
accretion from the companion sufficient to power the persistent emission from
the SGR.Comment: 11 pages, accepted for publication in ApJ Letter
Particle Emission-dependent Timing Noise of Pulsars?
Though pulsars spin regularly, the differences between the observed and
predicted ToA (time of arrival), known as "timing noise", can still reach a few
milliseconds or more. We try to understand the noise in this paper. As proposed
by Xu & Qiao in 2001, both dipole radiation and particle emission would result
in pulsar braking. Accordingly, possible fluctuation of particle current flow
is suggested here to contribute significant ToA variation of pulsars. We find
that the particle emission fluctuation could lead to timing noise which can't
be eliminated in timing process, and that a longer period fluctuation would
arouse a stronger noise. The simulated timing noise profile and amplitude are
in accord with the observed timing behaviors on the timescale of years.Comment: 6 pages, 2 figures. (Accepted by Chin. Phys. Lett.
Binary Pulsar Tests of General Relativity in the Presence of Low-Frequency Noise
The influence of the low-frequency timing noise on the precision of
measurements of the Keplerian and post-Keplerian orbital parameters in binary
pulsars is studied. Fundamental limits on the accuracy of tests of alternative
theories of gravity in the strong-field regime are established. The
gravitational low-frequency timing noise formed by an ensemble of binary stars
is briefly discussed.Comment: 4 pages, contributed paper to the proceedings of the IAU167
colloquium on pulsars, Bonn, August-September 199
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