16 research outputs found
The Mock LISA Data Challenges: from Challenge 3 to Challenge 4
The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis
capabilities and to encourage their development. Each round of challenges
consists of one or more datasets containing simulated instrument noise and
gravitational waves from sources of undisclosed parameters. Participants
analyze the datasets and report best-fit solutions for the source parameters.
Here we present the results of the third challenge, issued in Apr 2008, which
demonstrated the positive recovery of signals from chirping Galactic binaries,
from spinning supermassive--black-hole binaries (with optimal SNRs between ~ 10
and 2000), from simultaneous extreme-mass-ratio inspirals (SNRs of 10-50), from
cosmic-string-cusp bursts (SNRs of 10-100), and from a relatively loud
isotropic background with Omega_gw(f) ~ 10^-11, slightly below the LISA
instrument noise.Comment: 12 pages, 2 figures, proceedings of the 8th Edoardo Amaldi Conference
on Gravitational Waves, New York, June 21-26, 200
Comparing Recent Pulsar Timing Array Results on the Nanohertz Stochastic Gravitational-wave Background
The Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational-wave background (GWB). Given that each PTA made different choices in modeling their data, we perform a comparison of the GWB and individual pulsar noise parameters across the results reported from the PTAs that constitute the International Pulsar Timing Array (IPTA). We show that despite making different modeling choices, there is no significant difference in the GWB parameters that are measured by the different PTAs, agreeing within 1σ. The pulsar noise parameters are also consistent between different PTAs for the majority of the pulsars included in these analyses. We bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and PTAs, finding that under this model there is a reduction in the tension in the pulsar noise parameters. As part of this reanalysis, we "extended" each PTA's data set by adding extra pulsars that were not timed by that PTA. Under these extensions, we find better constraints on the GWB amplitude and a higher signal-to-noise ratio for the Hellings–Downs correlations. These extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the IPTA, i.e., the IPTA's Data Release 3, which will involve not just adding in additional pulsars but also including data from all three PTAs where any given pulsar is timed by more than a single PTA
Comparing recent PTA results on the nanohertz stochastic gravitational wave background
The Australian, Chinese, European, Indian, and North American pulsar timing
array (PTA) collaborations recently reported, at varying levels, evidence for
the presence of a nanohertz gravitational wave background (GWB). Given that
each PTA made different choices in modeling their data, we perform a comparison
of the GWB and individual pulsar noise parameters across the results reported
from the PTAs that constitute the International Pulsar Timing Array (IPTA). We
show that despite making different modeling choices, there is no significant
difference in the GWB parameters that are measured by the different PTAs,
agreeing within . The pulsar noise parameters are also consistent
between different PTAs for the majority of the pulsars included in these
analyses. We bridge the differences in modeling choices by adopting a
standardized noise model for all pulsars and PTAs, finding that under this
model there is a reduction in the tension in the pulsar noise parameters. As
part of this reanalysis, we "extended" each PTA's data set by adding extra
pulsars that were not timed by that PTA. Under these extensions, we find better
constraints on the GWB amplitude and a higher signal-to-noise ratio for the
Hellings and Downs correlations. These extensions serve as a prelude to the
benefits offered by a full combination of data across all pulsars in the IPTA,
i.e., the IPTA's Data Release 3, which will involve not just adding in
additional pulsars, but also including data from all three PTAs where any given
pulsar is timed by more than as single PTA.Comment: 21 pages, 9 figures, submitted to Ap
The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
We report multiple lines of evidence for a stochastic signal that is
correlated among 67 pulsars from the 15-year pulsar-timing data set collected
by the North American Nanohertz Observatory for Gravitational Waves. The
correlations follow the Hellings-Downs pattern expected for a stochastic
gravitational-wave background. The presence of such a gravitational-wave
background with a power-law-spectrum is favored over a model with only
independent pulsar noises with a Bayes factor in excess of , and this
same model is favored over an uncorrelated common power-law-spectrum model with
Bayes factors of 200-1000, depending on spectral modeling choices. We have
built a statistical background distribution for these latter Bayes factors
using a method that removes inter-pulsar correlations from our data set,
finding (approx. ) for the observed Bayes factors in the
null no-correlation scenario. A frequentist test statistic built directly as a
weighted sum of inter-pulsar correlations yields (approx. ). Assuming a fiducial
characteristic-strain spectrum, as appropriate for an ensemble of binary
supermassive black-hole inspirals, the strain amplitude is (median + 90% credible interval) at a reference frequency of
1/(1 yr). The inferred gravitational-wave background amplitude and spectrum are
consistent with astrophysical expectations for a signal from a population of
supermassive black-hole binaries, although more exotic cosmological and
astrophysical sources cannot be excluded. The observation of Hellings-Downs
correlations points to the gravitational-wave origin of this signal.Comment: 30 pages, 18 figures. Published in Astrophysical Journal Letters as
part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave
Background. For questions or comments, please email [email protected]
Comparing recent PTA results on the nanohertz stochastic gravitational wave background
Agazie G, Antoniadis J, Anumarlapudi A, et al. Comparing recent PTA results on the nanohertz stochastic gravitational wave background. 2023.The Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational wave background (GWB). Given that each PTA made different choices in modeling their data, we perform a comparison of the GWB and individual pulsar noise parameters across the results reported from the PTAs that constitute the International Pulsar Timing Array (IPTA). We show that despite making different modeling choices, there is no significant difference in the GWB parameters that are measured by the different PTAs, agreeing within . The pulsar noise parameters are also consistent between different PTAs for the majority of the pulsars included in these analyses. We bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and PTAs, finding that under this model there is a reduction in the tension in the pulsar noise parameters. As part of this reanalysis, we "extended" each PTA's data set by adding extra pulsars that were not timed by that PTA. Under these extensions, we find better constraints on the GWB amplitude and a higher signal-to-noise ratio for the Hellings and Downs correlations. These extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the IPTA, i.e., the IPTA's Data Release 3, which will involve not just adding in additional pulsars, but also including data from all three PTAs where any given pulsar is timed by more than as single PTA
The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background
The NANOGrav 15 yr data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such low-frequency gravitational waves, here we analyze the signal as coming from a population of supermassive black hole (SMBH) binaries distributed throughout the Universe. We show that astrophysically motivated models of SMBH binary populations are able to reproduce both the amplitude and shape of the observed low-frequency gravitational-wave spectrum. While multiple model variations are able to reproduce the GWB spectrum at our current measurement precision, our results highlight the importance of accurately modeling binary evolution for producing realistic GWB spectra. Additionally, while reasonable parameters are able to reproduce the 15 yr observations, the implied GWB amplitude necessitates either a large number of parameters to be at the edges of expected values or a small number of parameters to be notably different from standard expectations. While we are not yet able to definitively establish the origin of the inferred GWB signal, the consistency of the signal with astrophysical expectations offers a tantalizing prospect for confirming that SMBH binaries are able to form, reach subparsec separations, and eventually coalesce. As the significance grows over time, higher-order features of the GWB spectrum will definitively determine the nature of the GWB and allow for novel constraints on SMBH populations
The NANOGrav 15-year Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background
The NANOGrav 15-year data set shows evidence for the presence of a
low-frequency gravitational-wave background (GWB). While many physical
processes can source such low-frequency gravitational waves, here we analyze
the signal as coming from a population of supermassive black hole (SMBH)
binaries distributed throughout the Universe. We show that astrophysically
motivated models of SMBH binary populations are able to reproduce both the
amplitude and shape of the observed low-frequency gravitational-wave spectrum.
While multiple model variations are able to reproduce the GWB spectrum at our
current measurement precision, our results highlight the importance of
accurately modeling binary evolution for producing realistic GWB spectra.
Additionally, while reasonable parameters are able to reproduce the 15-year
observations, the implied GWB amplitude necessitates either a large number of
parameters to be at the edges of expected values, or a small number of
parameters to be notably different from standard expectations. While we are not
yet able to definitively establish the origin of the inferred GWB signal, the
consistency of the signal with astrophysical expectations offers a tantalizing
prospect for confirming that SMBH binaries are able to form, reach sub-parsec
separations, and eventually coalesce. As the significance grows over time,
higher-order features of the GWB spectrum will definitively determine the
nature of the GWB and allow for novel constraints on SMBH populations.Comment: Accepted by Astrophysical Journal Letters as part of Focus on
NANOGrav's 15-year Data Set and the Gravitational Wave Background. For
questions or comments, please email [email protected]
The NANOGrav 15-year Data Set: Search for Signals from New Physics
The 15-year pulsar timing data set collected by the North American Nanohertz
Observatory for Gravitational Waves (NANOGrav) shows positive evidence for the
presence of a low-frequency gravitational-wave (GW) background. In this paper,
we investigate potential cosmological interpretations of this signal,
specifically cosmic inflation, scalar-induced GWs, first-order phase
transitions, cosmic strings, and domain walls. We find that, with the exception
of stable cosmic strings of field theory origin, all these models can reproduce
the observed signal. When compared to the standard interpretation in terms of
inspiraling supermassive black hole binaries (SMBHBs), many cosmological models
seem to provide a better fit resulting in Bayes factors in the range from 10 to
100. However, these results strongly depend on modeling assumptions about the
cosmic SMBHB population and, at this stage, should not be regarded as evidence
for new physics. Furthermore, we identify excluded parameter regions where the
predicted GW signal from cosmological sources significantly exceeds the
NANOGrav signal. These parameter constraints are independent of the origin of
the NANOGrav signal and illustrate how pulsar timing data provide a new way to
constrain the parameter space of these models. Finally, we search for
deterministic signals produced by models of ultralight dark matter (ULDM) and
dark matter substructures in the Milky Way. We find no evidence for either of
these signals and thus report updated constraints on these models. In the case
of ULDM, these constraints outperform torsion balance and atomic clock
constraints for ULDM coupled to electrons, muons, or gluons.Comment: 74 pages, 31 figures, 4 tables; published in Astrophysical Journal
Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational
Wave Background. For questions or comments, please email
[email protected]