95 research outputs found
Known unknowns: assessing the impact of instrumental calibration uncertainty on LISA science
The primary scientific results of the future space-based gravitational wave interferometer LISA will come from the parameter inference of a large variety of gravitational wave sources. However, the presence of calibration errors could potentially degrade the measurement precision of the system parameters. Here, we assess the impact of calibration uncertainties on parameter estimation for individual sources, focusing on massive black holes, extreme-mass-ratio inspirals (EMRIs), galactic binaries, and stellar origin black hole binaries. Using a Fisher matrix formalism, we investigate how the measurement precision of source parameters degrades as a function of the size of the assumed calibration uncertainties. If we require that parameter measurements are degraded by no more than a factor of two relative to their value in the absence of calibration error, we find that calibration errors should be smaller than a few tenths of a percent in amplitude and in phase. We also investigate the possibility of using verification binaries and EMRIs to constrain calibration uncertainties. Verification binaries can constrain amplitude calibration uncertainties at the level of a few percent, while both source types can provide constrain phase calibration at the level of a few
Quality over Quantity: Optimizing pulsar timing array analysis for stochastic and continuous gravitational wave signals
The search for gravitational waves using Pulsar Timing Arrays (PTAs) is acomputationally expensive complex analysis that involves source-specific noisestudies. As more pulsars are added to the arrays, this stage of PTA analysiswill become increasingly challenging. Therefore, optimizing the number ofincluded pulsars is crucial to reduce the computational burden of dataanalysis. Here, we present a suite of methods to rank pulsars for use withinthe scope of PTA analysis. First, we use the maximization of thesignal-to-noise ratio as a proxy to select pulsars. With this method, we targetthe detection of stochastic and continuous gravitational wave signals. Next, wepresent a ranking that minimizes the coupling between spatial correlationsignatures, namely monopolar, dipolar, and Hellings & Downs correlations.Finally, we also explore how to combine these two methods. We test theseapproaches against mock data using frequentist and Bayesian hypothesis testing.For equal-noise pulsars, we find that an optimal selection leads to an increasein the log-Bayes factor two times steeper than a random selection for thehypothesis test of a gravitational wave background versus a common uncorrelatedred noise process. For the same test but for a realistic EPTA dataset, a subsetof 25 pulsars selected out of 40 can provide a log-likelihood ratio that is of the total, implying that an optimally selected subset of pulsars canyield results comparable to those obtained from the whole array. We expectthese selection methods to play a crucial role in future PTA data combinations.<br
FastEMRIWaveforms: New tools for millihertz gravitational-wave data analysis
We present the FastEMRIWaveforms (FEW) package, a collection of tools to
build and analyze extreme mass ratio inspiral (EMRI) waveforms. Here, we expand
on the Physical Review Letter that introduced the first fast and accurate
fully-relativistic EMRI waveform template model. We discuss the construction of
the overall framework; constituent modules; and the general methods used to
accelerate EMRI waveforms. Because the fully relativistic FEW model waveforms
are for now limited to eccentric orbits in the Schwarzschild spacetime, we also
introduce an improved Augmented Analytic Kludge (AAK) model that describes
generic Kerr inspirals. Both waveform models can be accelerated using graphics
processing unit (GPU) hardware. With the GPU-accelerated waveforms in hand, a
variety of studies are performed including an analysis of EMRI mode content,
template mismatch, and fully Bayesian Markov Chain Monte Carlo-based EMRI
parameter estimation. We find relativistic EMRI waveform templates can be
generated with fewer harmonic modes () without biasing signal
extraction. However, we show for the first time that extraction of a
relativistic injection with semi-relativistic amplitudes can lead to strong
bias and anomalous structure in the posterior distribution for certain regions
of parameter space.Comment: 26 pages, 12 Figures, FastEMRIWaveforms Package:
bhptoolkit.org/FastEMRIWaveforms
Constraining the evolution of Newton's constant with slow inspirals observed from spaceborne gravitational-wave detectors
Spaceborne gravitational-wave (GW) detectors observing at milli-Hz and
deci-Hz frequencies are expected to detect large numbers of quasi-monochromatic
signals. The first and second time-derivative of the GW frequency (
and ) can be measured for the most favourable sources and used to
look for negative post-Newtonian corrections, which can be induced by the
source's environment or modifications of general relativity. We present an
analytical, Fisher-matrix-based approach to estimate how precisely such
corrections can be constrained. We use this method to estimate the bounds
attainable on the time evolution of the gravitational constant with
different classes of quasi-monochromatic sources observable with LISA and
DECIGO, two representative spaceborne detectors for milli-Hz and deci-Hz GW
frequencies. We find that the most constraining source among a simulated
population of LISA galactic binaries could yield , while the best currently known verification binary will
reach . We also perform Monte-Carlo
simulations using quasi-monochromatic waveforms to check the validity of our
Fisher-matrix approach, as well as inspiralling waveforms to analyse binaries
that do not satisfy the quasi-monochromatic assumption. We find that our
analytical Fisher matrix produces good order-of-magnitude constraints even for
sources well beyond its regime of validity. Monte-Carlo investigations also
show that chirping stellar-mass compact binaries detected by DECIGO-like
detectors at cosmological distances of tens of Mpc can yield constraints as
tight as .Comment: 10 pages, 3 figure
Constraining the evolution of Newton's constant with slow inspirals observed from spaceborne gravitational-wave detectors
Spaceborne gravitational-wave (GW) detectors observing at milli-Hz and deci-Hz frequencies are expected to detect large numbers of quasi-monochromatic signals. The first and second time-derivative of the GW frequency ( and ) can be measured for the most favourable sources and used to look for negative post-Newtonian corrections, which can be induced by the source's environment or modifications of general relativity. We present an analytical, Fisher-matrix-based approach to estimate how precisely such corrections can be constrained. We use this method to estimate the bounds attainable on the time evolution of the gravitational constant with different classes of quasi-monochromatic sources observable with LISA and DECIGO, two representative spaceborne detectors for milli-Hz and deci-Hz GW frequencies. We find that the most constraining source among a simulated population of LISA galactic binaries could yield , while the best currently known verification binary will reach . We also perform Monte-Carlo simulations using quasi-monochromatic waveforms to check the validity of our Fisher-matrix approach, as well as inspiralling waveforms to analyse binaries that do not satisfy the quasi-monochromatic assumption. We find that our analytical Fisher matrix produces good order-of-magnitude constraints even for sources well beyond its regime of validity. Monte-Carlo investigations also show that chirping stellar-mass compact binaries detected by DECIGO-like detectors at cosmological distances of tens of Mpc can yield constraints as tight as
Probing Accretion Physics with Gravitational Waves
Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer
the opportunity to probe the environments of active galactic nuclei (AGN)
through the torques that accretion disks induce on the binary. Within a
Bayesian framework, we study how well such environmental effects can be
measured using gravitational wave observations from the Laser Interferometer
Space Antenna (LISA). We focus on the torque induced by planetary-type
migration on quasicircular inspirals, and use different prescriptions for
geometrically thin and radiatively efficient disks. We find that LISA could
detect migration for a wide range of disk viscosities and accretion rates, for
both and disk prescriptions. For a typical EMRI with masses
, we find that LISA could distinguish between migration
in and disks and measure the torque amplitude with
relative precision. Provided an accurate torque model, we also show how to turn
gravitational-wave measurements of the torque into constraints on the disk
properties. Furthermore, we show that, if an electromagnetic counterpart is
identified, the multimessenger observations of the AGN EMRI system will yield
direct measurements of the disk viscosity. Finally, we investigate the impact
of neglecting environmental effects in the analysis of the gravitational-wave
signal, finding 3 biases in the primary mass and spin, and showing that
ignoring such effects can lead to false detection of a deviation from general
relativity. This work demonstrates the scientific potential of gravitational
observations as probes of accretion-disk physics, accessible so far through
electromagnetic observations only
Fast and Fourier: Extreme Mass Ratio Inspiral Waveforms in the Frequency Domain
Extreme Mass Ratio Inspirals (EMRIs) are one of the key sources for future
space-based gravitational wave interferometers. Measurements of EMRI
gravitational waves are expected to determine the characteristics of their
sources with sub-percent precision. However, their waveform generation is
challenging due to the long duration of the signal and the high harmonic
content. Here, we present the first ready-to-use Schwarzschild eccentric EMRI
waveform implementation in the frequency domain for use with either graphics
processing units (GPUs) or central processing units (CPUs). We present the
overall waveform implementation and test the accuracy and performance of the
frequency domain waveforms against the time domain implementation. On GPUs, the
frequency domain waveform takes in median seconds to generate and is
twice as fast to compute as its time domain counterpart when considering
massive black hole masses and initial
eccentricities . On CPUs, the median waveform evaluation time is
seconds, and it is five times faster in the frequency domain than in the time
domain. Using a sparser frequency array can further speed up the waveform
generation, reaching up to seconds. This enables us to perform, for the
first time, EMRI parameter inference with fully relativistic waveforms on CPUs.
Future EMRI models which encompass wider source characteristics (particularly
black hole spin and generic orbit geometries) will require significantly more
harmonics. Frequency-domain models will be essential analysis tools for these
astrophysically realistic and important signals.Comment: 23 pages, 6 figure
Regulation, governance and agglomeration: making links in city-region research
This paper provides an overview and synthesis of debates pertaining to the development of city-regions and their applicability to the UK space economy. The purpose is to make links to advance both interna- tional academic debates and realpolitik policy knowledge concerns. The paper, firstly, traces the multifari- ous and at times disconnected academic discussions around the concepts of regionalism, city-regionalism and localism in the UK. Secondly, it considers the contemporary academic debates on the city-region, focusing in particular on those applicable to the current UK policy context. Given that city-regions are increasingly seen as the principal (and often unquestioned) consolidating spatial scale for economic and social development, the paper, thirdly, probes on the silent and missing aspects of the prescribed city-re- gion approach, connecting and contributing in turn to concerns with building inclusive-growth
Practical approaches to analyzing PTA data: Cosmic strings with six pulsars
We search for a stochastic gravitational wave background (SGWB) generated by
a network of cosmic strings using six millisecond pulsars from Data Release 2
(DR2) of the European Pulsar Timing Array (EPTA). We perform a Bayesian
analysis considering two models for the network of cosmic string loops, and
compare it to a simple power-law model which is expected from the population of
supermassive black hole binaries. Our main strong assumption is that the
previously reported common red noise process is a SGWB. We find that the
one-parameter cosmic string model is slightly favored over a power-law model
thanks to its simplicity. If we assume a two-component stochastic signal in the
data (supermassive black hole binary population and the signal from cosmic
strings), we get a upper limit on the string tension of () for the two cosmic string models we consider. In extended
two-parameter string models, we were unable to constrain the number of kinks.
We test two approximate and fast Bayesian data analysis methods against the
most rigorous analysis and find consistent results. These two fast and
efficient methods are applicable to all SGWBs, independent of their source, and
will be crucial for analysis of extended data sets.Comment: 13 pages, 5 figure
The second data release from the European Pulsar Timing Array I. The dataset and timing analysis
Pulsar timing arrays offer a probe of the low-frequency gravitational wave
spectrum (1 - 100 nanohertz), which is intimately connected to a number of
markers that can uniquely trace the formation and evolution of the Universe. We
present the dataset and the results of the timing analysis from the second data
release of the European Pulsar Timing Array (EPTA). The dataset contains
high-precision pulsar timing data from 25 millisecond pulsars collected with
the five largest radio telescopes in Europe, as well as the Large European
Array for Pulsars. The dataset forms the foundation for the search for
gravitational waves by the EPTA, presented in associated papers. We describe
the dataset and present the results of the frequentist and Bayesian pulsar
timing analysis for individual millisecond pulsars that have been observed over
the last ~25 years. We discuss the improvements to the individual pulsar
parameter estimates, as well as new measurements of the physical properties of
these pulsars and their companions. This data release extends the dataset from
EPTA Data Release 1 up to the beginning of 2021, with individual pulsar
datasets with timespans ranging from 14 to 25 years. These lead to improved
constraints on annual parallaxes, secular variation of the orbital period, and
Shapiro delay for a number of sources. Based on these results, we derived
astrophysical parameters that include distances, transverse velocities, binary
pulsar masses, and annual orbital parallaxes.Comment: 29 pages, 9 figures, 13 tables, Astronomy & Astrophysics in pres
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