35 research outputs found
Post-Newtonian-accurate pulsar timing array signals induced by inspiralling eccentric binaries: accuracy, computational cost, and single-pulsar search
Pulsar Timing Array (PTA) experiments are expected to be sensitive to
gravitational waves (GWs) emitted by individual supermassive black hole
binaries (SMBHBs) inspiralling along eccentric orbits. We compare the
computational cost of different methods of computing the PTA signals induced by
relativistic eccentric SMBHBs, namely approximate analytic expressions, Fourier
series expansion, post-circular expansion, and numerical integration. We show
that the fastest method for evaluating PTA signals is by using the approximate
analytic expressions, which provides up to ~50 times improvement in
computational speed over the alternative methods. We investigate the accuracy
of the approximate analytic expressions by employing a mismatch metric valid
for PTA signals. We show that this method is accurate within the region of the
binary parameter space that is of interest to PTA experiments. We introduce a
spline-based method to further accelerate the PTA signal evaluations for
narrowband PTA datasets. The efficient methods for computing the eccentric
SMBHB-induced PTA signals were implemented in the GWecc.jl package and can be
readily accessed from the popular ENTERPRISE package to search for such signals
in PTA datasets. Further, we simplify the eccentric SMBHB PTA signal expression
for the case of a single-pulsar search and demonstrate our computationally
efficient methods by performing a single-pulsar search in the 12.5-year
NANOGrav narrowband dataset of PSR J1909-3744 using the simplified expression.
These results will be crucial for searching for eccentric SMBHBs in large PTA
datasets.Comment: Accepted for publication in Classical and Quantum Gravit
Solving post-Newtonian accurate Kepler Equation
We provide an elegant way of solving analytically the third post-Newtonian
(3PN) accurate Kepler equation, associated with the 3PN-accurate generalized
quasi-Keplerian parametrization for compact binaries in eccentric orbits. An
additional analytic solution is presented to check the correctness of our
compact solution and we perform comparisons between our PN-accurate analytic
solution and a very accurate numerical solution of the PN-accurate Kepler
equation. We adapt our approach to compute crucial 3PN-accurate inputs that
will be required to compute analytically both the time and frequency domain
ready-to-use amplitude-corrected PN-accurate search templates for compact
binaries in inspiralling eccentric orbits.Comment: 20 pages, 4 figure
Noise analysis of the Indian Pulsar Timing Array data release I
The Indian Pulsar Timing Array (InPTA) collaboration has recently made its first official data release (DR1) for a sample of 14 pulsars using 3.5 years of uGMRT observations. We present the results of single-pulsar noise analysis for each of these 14 pulsars using the InPTA DR1. For this purpose, we consider white noise, achromatic red noise, dispersion measure (DM) variations, and scattering variations in our analysis. We apply Bayesian model selection to obtain the preferred noise models among these for each pulsar. For PSR J1600â3053, we find no evidence of DM and scattering variations, while for PSR J1909â3744, we find no significant scattering variations. Properties vary dramatically among pulsars. For example, we find a strong chromatic noise with chromatic index ⌠2.9 for PSR J1939+2134, indicating the possibility of a scattering index that doesnât agree with that expected for a Kolmogorov scattering medium consistent with similar results for millisecond pulsars in past studies. Despite the relatively short time baseline, the noise models broadly agree with the other PTAs and provide, at the same time, well-constrained DM and scattering variations
High Precision Measurements of Interstellar Dispersion Measure with the upgraded GMRT
Pulsar radio emission undergoes dispersion due to the presence of free
electrons in the interstellar medium (ISM). The dispersive delay in the arrival
time of pulsar signal changes over time due to the varying ISM electron column
density along the line of sight. Correcting for this delay accurately is
crucial for the detection of nanohertz gravitational waves using Pulsar Timing
Arrays. In this work, we present in-band and inter-band DM estimates of four
pulsars observed with uGMRT over the timescale of a year using two different
template alignment methods. The DMs obtained using both these methods show only
subtle differences for PSR 1713+0747 and J19093744. A considerable offset is
seen in the DM of PSR J1939+2134 and J21450750 between the two methods. This
could be due to the presence of scattering in the former and profile evolution
in the latter. We find that both methods are useful but could have a systematic
offset between the DMs obtained. Irrespective of the template alignment methods
followed, the precision on the DMs obtained is about pc cm
using only BAND3 and pc cm after combining data from BAND3 and
BAND5 of the uGMRT. In a particular result, we have detected a DM excess of
about pc cm on 24 February 2019 for PSR J21450750.
This excess appears to be due to the interaction region created by fast solar
wind from a coronal hole and a coronal mass ejection (CME) observed from the
Sun on that epoch. A detailed analysis of this interesting event is presented.Comment: 11 pages, 6 figures, 2 tables. Accepted by A&
Multi-band Extension of the Wideband Timing Technique
The wideband timing technique enables the high-precision simultaneous
estimation of Times of Arrival (ToAs) and Dispersion Measures (DMs) while
effectively modeling frequency-dependent profile evolution. We present two
novel independent methods that extend the standard wideband technique to handle
simultaneous multi-band pulsar data incorporating profile evolution over a
larger frequency span to estimate DMs and ToAs with enhanced precision. We
implement the wideband likelihood using the libstempo python interface to
perform wideband timing in the tempo2 framework. We present the application of
these techniques to the dataset of fourteen millisecond pulsars observed
simultaneously in Band 3 (300 - 500 MHz) and Band 5 (1260 - 1460 MHz) of the
upgraded Giant Metrewave Radio Telescope (uGMRT) as a part of the Indian Pulsar
Timing Array (InPTA) campaign. We achieve increased ToA and DM precision and
sub-microsecond root mean square post-fit timing residuals by combining
simultaneous multi-band pulsar observations done in non-contiguous bands for
the first time using our novel techniques.Comment: Submitted to MNRA
Noise analysis of the Indian Pulsar Timing Array data release I
The Indian Pulsar Timing Array (InPTA) collaboration has recently made its
first official data release (DR1) for a sample of 14 pulsars using 3.5 years of
uGMRT observations. We present the results of single-pulsar noise analysis for
each of these 14 pulsars using the InPTA DR1. For this purpose, we consider
white noise, achromatic red noise, dispersion measure (DM) variations, and
scattering variations in our analysis. We apply Bayesian model selection to
obtain the preferred noise models among these for each pulsar. For PSR
J16003053, we find no evidence of DM and scattering variations, while for
PSR J19093744, we find no significant scattering variations. Properties vary
dramatically among pulsars. For example, we find a strong chromatic noise with
chromatic index 2.9 for PSR J1939+2134, indicating the possibility of a
scattering index that doesn't agree with that expected for a Kolmogorov
scattering medium consistent with similar results for millisecond pulsars in
past studies. Despite the relatively short time baseline, the noise models
broadly agree with the other PTAs and provide, at the same time,
well-constrained DM and scattering variations.Comment: Accepted for publication in PRD, 30 pages, 17 figures, 4 table