238 research outputs found

### Practical Methods for Continuous Gravitational Wave Detection using Pulsar Timing Data

Gravitational Waves (GWs) are tiny ripples in the fabric of space-time
predicted by Einstein's General Relativity. Pulsar timing arrays (PTAs) are
well poised to detect low frequency ($10^{-9}$ -- $10^{-7}$ Hz) GWs in the near
future. There has been a significant amount of research into the detection of a
stochastic background of GWs from supermassive black hole binaries (SMBHBs).
Recent work has shown that single continuous sources standing out above the
background may be detectable by PTAs operating at a sensitivity sufficient to
detect the stochastic background. The most likely sources of continuous GWs in
the pulsar timing frequency band are extremely massive and/or nearby SMBHBs. In
this paper we present detection strategies including various forms of matched
filtering and power spectral summing. We determine the efficacy and
computational cost of such strategies. It is shown that it is computationally
infeasible to use an optimal matched filter including the poorly constrained
pulsar distances with a grid based method. We show that an Earth-term-matched
filter constructed using only the correlated signal terms is both
computationally viable and highly sensitive to GW signals. This technique is
only a factor of two less sensitive than the computationally unrealizable
optimal matched filter and a factor of two more sensitive than a power spectral
summing technique. We further show that a pairwise matched filter, taking the
pulsar distances into account is comparable to the optimal matched filter for
the single template case and comparable to the Earth-term-matched filter for
many search templates. Finally, using simulated data optimal quality, we place
a theoretical minimum detectable strain amplitude of $h>2\times 10^{-15}$ from
continuous GWs at frequencies on the order $\sim1/T_{\rm obs}$.Comment: submitted to Ap

### Detection of variable frequency signals using a fast chirp transform

The detection of signals with varying frequency is important in many areas of
physics and astrophysics. The current work was motivated by a desire to detect
gravitational waves from the binary inspiral of neutron stars and black holes,
a topic of significant interest for the new generation of interferometric
gravitational wave detectors such as LIGO. However, this work has significant
generality beyond gravitational wave signal detection.
We define a Fast Chirp Transform (FCT) analogous to the Fast Fourier
Transform (FFT). Use of the FCT provides a simple and powerful formalism for
detection of signals with variable frequency just as Fourier transform
techniques provide a formalism for the detection of signals of constant
frequency. In particular, use of the FCT can alleviate the requirement of
generating complicated families of filter functions typically required in the
conventional matched filtering process. We briefly discuss the application of
the FCT to several signal detection problems of current interest

### Constraining the coalescence rate of supermassive black-hole binaries using pulsar timing

Pulsar timing observations are used to place constraints on the rate of
coalescence of supermassive black-hole (SMBH) binaries as a function of mass
and redshift. In contrast to the indirect constraints obtained from other
techniques, pulsar timing observations provide a direct constraint on the
black-hole merger rate. This is possible since pulsar timing is sensitive to
the gravitational waves (GWs) emitted by these sources in the final stages of
their evolution. We find that upper bounds calculated from the recently
published Parkes Pulsar Timing Array data are just above theoretical
predictions for redshifts below 10. In the future, with improved timing
precision and longer data spans, we show that a non-detection of GWs will rule
out some of the available parameter space in a particular class of SMBH binary
merger models. We also show that if we can time a set of pulsars to 10ns timing
accuracy, for example, using the proposed Square Kilometre Array, it should be
possible to detect one or more individual SMBH binary systems

### Detecting gravitational wave memory with pulsar timing

We compare the detectability of gravitational bursts passing through the solar system with those passing near each millisecond pulsar in an N-pulsar timing array. The sensitivity to Earth-passing bursts can exploit the correlation expected in pulse arrival times while pulsar-passing bursts, though uncorrelated between objects, provide an N-fold increase in overall time baseline that can compensate for the lower sensitivity. Bursts with memory from mergers of supermassive black holes produce step functions in apparent spin frequency that are the easiest to detect in pulsar timing. We show that the burst rate and amplitude distribution, while strongly dependent on inadequately known cosmological evolution, may favor detection in the pulsar terms rather than the Earth timing perturbations. Any contamination of timing data by red spin noise makes burst detection more difficult because both signals grow with the length of the time data span T. Furthermore, the different bursts that could appear in one or more data sets of length T 10yr also affect the detectability of the gravitational wave stochastic background that, like spin noise, has a red power spectrum. A burst with memory is a worthwhile target in the timing of multiple pulsars in a globular cluster because it should produce a correlated signal with a time delay of less than about 10years in some cases. Ã‚Â© 2012. The American Astronomical Society. All rights reserved.

### Radio Pulse Properties of the Millisecond Pulsar PSR J0437-4715. I. Observations at 20cm

We present a total of 48 minutes of observations of the nearby, bright
millisecond pulsar PSR J0437-4715 taken at the Parkes radio observatory in
Australia. The data were obtained at a central radio frequency of 1380 MHz
using a high-speed tape recorder that permitted coherent Nyquist sampling of 50
MHz of bandwidth in each of two polarizations. Using the high time resolution
available from this voltage recording technique, we have studied a variety of
single-pulse properties, most for the first time in a millisecond pulsar. We
find no evidence for "diffractive" quantization effects in the individual pulse
arrival times or amplitudes as have been reported for this pulsar at lower
radio frequency using coarser time resolution (Ables et al. 1997). Overall, we
find that the single pulse properties of PSR J0437-4715 are similar to those of
the common slow-rotating pulsars, even though this pulsar's magnetosphere and
surface magnetic field are several orders of magnitude smaller than those of
the general population. The pulsar radio emission mechanism must therefore be
insensitive to these fundamental neutron star properties.Comment: 24 Postscript pages, 11 eps figures. Accepted for publication in the
Astrophysical Journal. Abbreviated abstract follow

### Search for Electromagnetic Counterparts to LIGO-Virgo Candidates: Expanded Very Large Array

This paper summarizes a search for radio wavelength counterparts to candidate
gravitational wave events. The identification of an electromagnetic counterpart
could provide a more complete understanding of a gravitational wave event,
including such characteristics as the location and the nature of the
progenitor. We used the Expanded Very Large Array (EVLA) to search six galaxies
which were identified as potential hosts for two candidate gravitational wave
events. We summarize our procedures and discuss preliminary results.Comment: 4 pages; to appear in the New Horizons in Time Domain Astronomy,
Proceedings of IAU Symposium 285, eds. R. E. M. Griffin, R. J. Hanisch & R.
Seama

### Pulsar timing and spacetime curvature

We analyze the effect of weak field gravitational waves on the timing of pulsars, with particular attention to gauge invariance, that is, to the effects that are independent of the choice of coordinates. We find (1) the Doppler shift cannot be separated into gauge invariant gravitational wave and kinetic contributions; (2) a gauge invariant separation can be made for the time derivative of the Doppler shift in which the gravitational wave contribution is directly related to the Riemann tensor, and the kinetic contribution is that for special relativity; (3) the gaugedependent effects in the Doppler shift play no role in the program of gravitational wave detection via pulsar timing. The direct connection shown between pulsar timing and the Riemann tensor of the gravitational waves will be of importance in discussions of gravitational waves from alternative (non-Einsteinian) theories of gravitation

### A coherent method for the detection and parameter estimation of continuous gravitational wave signals using a pulsar timing array

The use of a high precision pulsar timing array is a promising approach to detecting gravitational waves in the very low frequency regime (10-6-10-9 Hz) that is complementary to ground-based efforts (e.g., LIGO, Virgo) at high frequencies (Ã¢Ë†Â¼10-103 Hz) and space-based ones (e.g., LISA) at low frequencies (10-4-10-1 Hz). One of the target sources for pulsar timing arrays is individual supermassive black hole binaries which are expected to form in galactic mergers. In this paper, a likelihood-based method for detection and parameter estimation is presented for a monochromatic continuous gravitational wave signal emitted by such a source. The so-called pulsar terms in the signal that arise due to the breakdown of the long-wavelength approximation are explicitly taken into account in this method. In addition, the method accounts for equality and inequality constraints involved in the semi-analytical maximization of the likelihood over a subset of the parameters. The remaining parameters are maximized over numerically using Particle Swarm Optimization. Thus, the method presented here solves the monochromatic continuous wave detection and parameter estimation problem without invoking some of the approximations that have been used in earlier studies

### Electromagnetic Strong Plasma Turbulence

The first large-scale simulations of continuously driven, two-dimensional electromagnetic strong plasma turbulence are performed, for electron thermal speeds 0.01câ©½vâ©½0.57c, by integrating the Zakharov equations for coupled Langmuir and transverse (T) waves near the plasma frequency. Turbulence scalings and wave number spectra are calculated, a transition is found from a mix of trapped and free T eigenstates for vâ©¾0.1c to just free eigenstates for vâ©½0.1c, and wave energy densities are observed to undergo slow quasiperiodic oscillations

### Single Pulse Characteristics of the Millisecond Radio Pulsar PSR B1937+21 at 430 MHz

The single-pulse characteristics of the millisecond pulsar PSR B1937+21 are studied using the recently installed Caltech baseband recorder at the Arecibo Radio Observatory in Puerto Rico. This is the first such analysis of this object that includes both average intensity pulses as well as "giant pulses." Pulse ensemble-averaging techniques are developed in order to study the characteristics of PSR B1937+21's single pulses since the high time resolution signal-to-noise ratio is less than unity. This analysis reveals that the non-giant pulse radio emission is extremely stable. All observed fluctuations are consistent with diffractive interstellar scattering. Such intrinsic stability has yet to be observed in other radio pulsars

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