145 research outputs found
Cyclic Spectral Analysis of Radio Pulsars
Cyclic spectral analysis is a signal processing technique designed to deal
with stochastic signals whose statistics vary periodically with time. Pulsar
radio emission is a textbook example of this signal class, known as
cyclostationary signals. In this paper, we discuss the application of cyclic
spectral analysis methods to pulsar data, and compare the results with the
traditional filterbank approaches used for almost all pulsar observations to
date. In contrast to standard methods, the cyclic spectrum preserves phase
information of the radio signal. This feature allows us to determine the
impulse response of the interstellar medium and the intrinsic, unscattered
pulse profile directly from a single observation. We illustrate these new
analysis techniques using real data from an observation of the millisecond
pulsar B1937+21.Comment: Accepted for publication in MNRA
Pulsar data analysis with PSRCHIVE
PSRCHIVE is an open-source, object-oriented, scientific data analysis
software library and application suite for pulsar astronomy. It implements an
extensive range of general-purpose algorithms for use in data calibration and
integration, statistical analysis and modeling, and visualisation. These are
utilised by a variety of applications specialised for tasks such as pulsar
timing, polarimetry, radio frequency interference mitigation, and pulse
variability studies. This paper presents a general overview of PSRCHIVE
functionality with some focus on the integrated interfaces developed for the
core applications.Comment: 21 pages, 5 figures; tutorial presented at IPTA 2010 meeting in
Leiden merged with talk presented at 2011 pulsar conference in Beijing;
includes further research and development on algorithms for RFI mitigation
and TOA bias correctio
The Massive Pulsar PSR J1614-2230: Linking Quantum Chromodynamics, Gamma-ray Bursts, and Gravitational Wave Astronomy
The recent measurement of the Shapiro delay in the radio pulsar PSR
J1614-2230 yielded a mass of 1.97 +/- 0.04 M_sun, making it the most massive
pulsar known to date. Its mass is high enough that, even without an
accompanying measurement of the stellar radius, it has a strong impact on our
understanding of nuclear matter, gamma-ray bursts, and the generation of
gravitational waves from coalescing neutron stars. This single high mass value
indicates that a transition to quark matter in neutron-star cores can occur at
densities comparable to the nuclear saturation density only if the quarks are
strongly interacting and are color superconducting. We further show that a high
maximum neutron-star mass is required if short duration gamma-ray bursts are
powered by coalescing neutron stars and, therefore, this mechanism becomes
viable in the light of the recent measurement. Finally, we argue that the
low-frequency (<= 500 Hz) gravitational waves emitted during the final stages
of neutron-star coalescence encode the properties of the equation of state
because neutron stars consistent with this measurement cannot be centrally
condensed. This will facilitate the measurement of the neutron star equation of
state with Advanced LIGO/Virgo.Comment: Accepted for publication in ApJ
Multimessenger Approaches to Supermassive Black Hole Binary Detection and Parameter Estimation II: Optimal Strategies for a Pulsar Timing Array
Pulsar timing arrays (PTAs) are Galactic-scale gravitational wave (GW)
detectors consisting of precisely-timed pulsars distributed across the sky.
Within the decade, PTAs are expected to detect the nanohertz GWs emitted by
close-separation supermassive black hole binaries (SMBHBs), thereby opening up
the low frequency end of the GW spectrum for science. Individual SMBHBs which
power active galactic nuclei are also promising multi-messenger sources; they
may be identified via theoretically predicted electromagnetic (EM) signatures
and be followed up by PTAs for GW observations. In this work, we study the
detection and parameter estimation prospects of a PTA which targets EM-selected
SMBHBs. Adopting a simulated Galactic millisecond pulsar population, we
envisage three different pulsar timing campaigns which observe three mock
sources at different sky locations. We find that an all-sky PTA which times the
best pulsars is an optimal and feasible approach to observe EM-selected SMBHBs
and measure their source parameters to high precision (i.e., comparable to or
better than conventional EM measurements). We discuss the implications of our
findings in the context of the future PTA experiment with the planned Deep
Synoptic Array-2000 and the multi-messenger studies of SMBHBs such as the
well-known binary candidate OJ 287.Comment: 14 pages, 6 figures, 3 tables; ApJ accepted; data will be available
with the ApJ publicatio
Correcting For Interstellar Scattering Delay In High-Precision Pulsar Timing: Simulation Results
Light travel time changes due to gravitational waves (GWs) may be detected within the next decade through precision timing of millisecond pulsars. Removal of frequency-dependent interstellar medium (ISM) delays due to dispersion and scattering is a key issue in the detection process. Current timing algorithms routinely correct pulse times of arrival (TOAs) for time-variable delays due to cold plasma dispersion. However, none of the major pulsar timing groups correct for delays due to scattering from multi-path propagation in the ISM. Scattering introduces a frequency-dependent phase change in the signal that results in pulse broadening and arrival time delays. Any method to correct the TOA for interstellar propagation effects must be based on multi-frequency measurements that can effectively separate dispersion and scattering delay terms from frequency-independent perturbations such as those due to a GW. Cyclic spectroscopy, first described in an astronomical context by Demorest (2011), is a potentially powerful tool to assist in this multi-frequency decomposition. As a step toward a more comprehensive ISM propagation delay correction, we demonstrate through a simulation that we can accurately recover impulse response functions (IRFs), such as those that would be introduced by multi-path scattering, with a realistic signal-to-noise ratio (S/N). We demonstrate that timing precision is improved when scatter-corrected TOAs are used, under the assumptions of a high S/N and highly scattered signal. We also show that the effect of pulse-to-pulse jitter is not a serious problem for IRF reconstruction, at least for jitter levels comparable to those observed in several bright pulsars
- …