36 research outputs found
MeerKAT Pulsar Timing Array parallaxes and proper motions
We have determined positions, proper motions, and parallaxes of
millisecond pulsars (MSPs) from years of MeerKAT radio telescope
observations. Our timing and noise analyses enable us to measure
significant parallaxes ( of them for the first time) and significant
proper motions. Eight pulsars near the ecliptic have an accurate proper motion
in ecliptic longitude only. PSR~J09556150 has a good upper limit on its very
small proper motion (0.4 mas yr). We used pulsars with accurate
parallaxes to study the MSP velocities. This yields MSP transverse
velocities, and combined with MSPs in the literature (excluding those in
Globular Clusters) we analyse MSPs in total. We find that MSPs have, on
average, much lower velocities than normal pulsars, with a mean transverse
velocity of only km s (MSPs) compared with km s
(normal pulsars). We found no statistical differences between the velocity
distributions of isolated and binary millisecond pulsars. From Galactocentric
cylindrical velocities of the MSPs, we derive 3-D velocity dispersions of
, , = , , km
s. We measure a mean asymmetric drift with amplitude km
s, consistent with expectation for MSPs, given their velocity
dispersions and ages. The MSP velocity distribution is consistent with binary
evolution models that predict very few MSPs with velocities km s
and a mild anticorrelation of transverse velocity with orbital period
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
The NANOGrav 12.5-Year Data Set: Dispersion Measure Mis-Estimation with Varying Bandwidths
Noise characterization for pulsar-timing applications accounts for
interstellar dispersion by assuming a known frequency-dependence of the delay
it introduces in the times of arrival (TOAs). However, calculations of this
delay suffer from mis-estimations due to other chromatic effects in the
observations. The precision in modeling dispersion is dependent on the observed
bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs
due to mis-estimations in the modeling of dispersion when using varying
bandwidths at the Green Bank Telescope. We use a set of broadband observations
of PSR J1643-1224, a pulsar with an excess of chromatic noise in its timing
residuals. We artificially restricted these observations to a narrowband
frequency range, then used both data sets to calculate residuals with a timing
model that does not include short-scale dispersion variations. By fitting the
resulting residuals to a dispersion model, and comparing the ensuing fitted
parameters, we quantify the dispersion mis-estimations. Moreover, by
calculating the autocovariance function of the parameters we obtained a
characteristic timescale over which the dispersion mis-estimations are
correlated. For PSR J1643-1224, which has one of the highest dispersion
measures (DM) in the NANOGrav pulsar timing array, we find that the
infinite-frequency TOAs suffer from a systematic offset of ~22 microseconds due
to DM mis-estimations, with correlations over ~1 month. For lower-DM pulsars,
the offset is ~7 microseconds. This error quantification can be used to provide
more robust noise modeling in NANOGrav's data, thereby increasing sensitivity
and improving parameter estimation in gravitational wave searches.Comment: 15 pages, 7 figure
The NANOGrav 12.5-Year Data Set:Dispersion Measure Misestimations with Varying Bandwidths
Noise characterization for pulsar-timing applications accounts for interstellar dispersion by assuming a known frequency dependence of the delay it introduces in the times of arrival (TOAs). However, calculations of this delay suffer from misestimations due to other chromatic effects in the observations. The precision in modeling dispersion is dependent on the observed bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs due to misestimations in the modeling of dispersion when using varying bandwidths at the Green Bank Telescope. We use a set of broadband observations of PSR J1643−1224, a pulsar with unusual chromatic timing behavior. We artificially restricted these observations to a narrowband frequency range, then used both the broad- and narrowband data sets to calculate residuals with a timing model that does not account for time variations in the dispersion. By fitting the resulting residuals to a dispersion model and comparing the fits, we quantify the error introduced in the timing parameters due to using a reduced frequency range. Moreover, by calculating the autocovariance function of the parameters, we obtained a characteristic timescale over which the dispersion misestimates are correlated. For PSR J1643−1224, which has one of the highest dispersion measures (DM) in the NANOGrav pulsar timing array, we find that the infinite-frequency TOAs suffer from a systematic offset of ∼22 μs due to incomplete frequency sampling, with correlations over about one month. For lower-DM pulsars, the offset is ∼7 μs. This error quantification can be used to provide more robust noise modeling in the NANOGrav data, thereby increasing the sensitivity and improving the parameter estimation in gravitational wave searches
Multimessenger Gravitational-wave Searches with Pulsar Timing Arrays:Application to 3C 66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 109 M o˙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over "blind"pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences
The NANOGrav 12.5 yr Data Set: Search for Gravitational Wave Memory
We present the results of a Bayesian search for gravitational wave (GW) memory in the NANOGrav 12.5 yr data set. We find no convincing evidence for any gravitational wave memory signals in this data set. We find a Bayes factor of 2.8 in favor of a model that includes a memory signal and common spatially uncorrelated red noise (CURN) compared to a model including only a CURN. However, further investigation shows that a disproportionate amount of support for the memory signal comes from three dubious pulsars. Using a more flexible red-noise model in these pulsars reduces the Bayes factor to 1.3. Having found no compelling evidence, we go on to place upper limits on the strain amplitude of GW memory events as a function of sky location and event epoch. These upper limits are computed using a signal model that assumes the existence of a common, spatially uncorrelated red noise in addition to a GW memory signal. The median strain upper limit as a function of sky position is approximately 3.3 × 10−14. We also find that there are some differences in the upper limits as a function of sky position centered around PSR J0613−0200. This suggests that this pulsar has some excess noise that can be confounded with GW memory. Finally, the upper limits as a function of burst epoch continue to improve at later epochs. This improvement is attributable to the continued growth of the pulsar timing array
The NANOGrav 12.5 yr Data Set: A Computationally Efficient Eccentric Binary Search Pipeline and Constraints on an Eccentric Supermassive Binary Candidate in 3C 66B
The radio galaxy 3C 66B has been hypothesized to host a supermassive black hole binary (SMBHB) at its center based on electromagnetic observations. Its apparent 1.05 yr period and low redshift (∼0.02) make it an interesting testbed to search for low-frequency gravitational waves (GWs) using pulsar timing array (PTA) experiments. This source has been subjected to multiple searches for continuous GWs from a circular SMBHB, resulting in progressively more stringent constraints on its GW amplitude and chirp mass. In this paper, we develop a pipeline for performing Bayesian targeted searches for eccentric SMBHBs in PTA data sets, and test its efficacy by applying it to simulated data sets with varying injected signal strengths. We also search for a realistic eccentric SMBHB source in 3C 66B using the NANOGrav 12.5 yr data set employing PTA signal models containing Earth term-only as well as Earth+pulsar term contributions using this pipeline. Due to limitations in our PTA signal model, we get meaningful results only when the initial eccentricity e 0 < 0.5 and the symmetric mass ratio η > 0.1. We find no evidence for an eccentric SMBHB signal in our data, and therefore place 95% upper limits on the PTA signal amplitude of 88.1 ± 3.7 ns for the Earth term-only and 81.74 ± 0.86 ns for the Earth+pulsar term searches for e 0 < 0.5 and η > 0.1. Similar 95% upper limits on the chirp mass are (1.98 ± 0.05) × 109 and (1.81 ± 0.01) × 109 M ☉. These upper limits, while less stringent than those calculated from a circular binary search in the NANOGrav 12.5 yr data set, are consistent with the SMBHB model of 3C 66B developed from electromagnetic observations
The NANOGrav 12.5-year data set: A computationally efficient eccentric binary search pipeline and constraints on an eccentric supermassive binary candidate in 3C 66B
The radio galaxy 3C 66B has been hypothesized to host a supermassive black
hole binary (SMBHB) at its center based on electromagnetic observations. Its
apparent 1.05-year period and low redshift () make it an interesting
testbed to search for low-frequency gravitational waves (GWs) using Pulsar
Timing Array (PTA) experiments. This source has been subjected to multiple
searches for continuous GWs from a circular SMBHB, resulting in progressively
more stringent constraints on its GW amplitude and chirp mass. In this paper,
we develop a pipeline for performing Bayesian targeted searches for eccentric
SMBHBs in PTA data sets, and test its efficacy by applying it on simulated data
sets with varying injected signal strengths. We also search for a realistic
eccentric SMBHB source in 3C 66B using the NANOGrav 12.5-year data set
employing PTA signal models containing Earth term-only as well as Earth+Pulsar
term contributions using this pipeline. Due to limitations in our PTA signal
model, we get meaningful results only when the initial eccentricity
and the symmetric mass ratio . We find no evidence for an eccentric
SMBHB signal in our data, and therefore place 95% upper limits on the PTA
signal amplitude of ns for the Earth term-only and
ns for the Earth+Pulsar term searches for . Similar 95%
upper limits on the chirp mass are and
. These upper limits, while less
stringent than those calculated from a circular binary search in the NANOGrav
12.5-year data set, are consistent with the SMBHB model of 3C 66B developed
from electromagnetic observations.Comment: 27 Pages, 10 Figures, 1 Table, Accepted for publication in Ap
The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars
We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. All were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. The timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of significant orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. A companion paper uses these data to constrain the strength of the gravitational-wave background