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UVB Radiation Affects the Quality of the Female Sexual Attractiveness Pheromone of the Red-Sided Garter Snake
In this study, pheromone and skin lipid samples collected from red-sided garter snakes (Thamnophis sirtalis parietalis) were exposed directly to either full-spectrum light or full-spectrum plus UVB light. In addition, female and male snakes were exposed to daily doses of either full-spectrum or full-spectrum and UVB light, after which the skin lipids were collected and analyzed. Behavioral studies were conducted on the snakes during exposure. After each experiment, the pheromone and other lipids were weighed and qualitatively and quantitatively analyzed by gas chromatography and mass spectrometry. The results show that UVB radiation reduces the unsaturated:saturated and the high-molecular weight:low-molecular weight methyl ketone ratios of the pheromone, which are correlated with the level of attractiveness of a female snake, in directly exposed samples. The unsaturated:saturated ratio was also decreased in live female snakes. No behavioral differences were observed, indicating that snakes do not attempt to shelter themselves from UVB light and appear to be unaware of UVB differences. These results suggest that an increase in UVB radiation, as has been occurring in the red-sided garter snakes' native range in Canada, could have an effect on the mating behavior of the snakes, leading to changes in the timing of critical life-history events such as breeding and dispersal for feeding
Efficient Gravitational Wave Searches with Pulsar Timing Arrays using Hamiltonian Monte Carlo
Pulsar timing arrays (PTAs) detect low-frequency gravitational waves (GWs) by
looking for correlated deviations in pulse arrival times. Current Bayesian
searches use Markov Chain Monte Carlo (MCMC) methods, which struggle to sample
the large number of parameters needed to model the PTA and GW signals. As the
data span and number of pulsars increase, this problem will only worsen. An
alternative Monte Carlo sampling method, Hamiltonian Monte Carlo (HMC),
utilizes Hamiltonian dynamics to produce sample proposals informed by
first-order gradients of the model likelihood. This in turn allows it to
converge faster to high dimensional distributions. We implement HMC as an
alternative sampling method in our search for an isotropic stochastic GW
background, and show that this method produces equivalent statistical results
to similar analyses run with standard MCMC techniques, while requiring 100-200
times fewer samples. We show that the speed of HMC sample generation scales as
where is the number of
pulsars, compared to for MCMC methods. These
factors offset the increased time required to generate a sample using HMC,
demonstrating the value of adopting HMC techniques for PTAs.Comment: 9 pages, 5 figures, submitted to Physical Review
Bumpy Black Holes in Alternate Theories of Gravity
We generalize the bumpy black hole framework to allow for alternative theory
deformations. We construct two model-independent parametric deviations from the
Kerr metric: one built from a generalization of the quasi-Kerr and bumpy
metrics and one built directly from perturbations of the Kerr spacetime in
Lewis-Papapetrou form. We find the conditions that these "bumps" must satisfy
for there to exist an approximate second-order Killing tensor so that the
perturbed spacetime still possesses three constants of the motion (a deformed
energy, angular momentum and Carter constant) and the geodesic equations can be
written in first-order form. We map these parameterized metrics to each other
via a diffeomorphism and to known analytical black hole solutions in
alternative theories of gravity. The parameterized metrics presented here serve
as frameworks for the systematic calculation of extreme-mass ratio inspiral
waveforms in parameterized non-GR theories and the investigation of the
accuracy to which space-borne gravitational wave detectors can constrain such
deviations.Comment: 17 pages, replaced with version published in Phys. Rev.
The scientific potential of space-based gravitational wave detectors
The millihertz gravitational wave band can only be accessed with a
space-based interferometer, but it is one of the richest in potential sources.
Observations in this band have amazing scientific potential. The mergers
between massive black holes with mass in the range 10 thousand to 10 million
solar masses, which are expected to occur following the mergers of their host
galaxies, produce strong millihertz gravitational radiation. Observations of
these systems will trace the hierarchical assembly of structure in the Universe
in a mass range that is very difficult to probe electromagnetically. Stellar
mass compact objects falling into such black holes in the centres of galaxies
generate detectable gravitational radiation for several years prior to the
final plunge and merger with the central black hole. Measurements of these
systems offer an unprecedented opportunity to probe the predictions of general
relativity in the strong-field and dynamical regime. Millihertz gravitational
waves are also generated by millions of ultra-compact binaries in the Milky
Way, providing a new way to probe galactic stellar populations. ESA has
recognised this great scientific potential by selecting The Gravitational
Universe as its theme for the L3 large satellite mission, scheduled for launch
in ~2034. In this article we will review the likely sources for millihertz
gravitational wave detectors and describe the wide applications that
observations of these sources could have for astrophysics, cosmology and
fundamental physics.Comment: 18 pages, 2 figures, contribution to Gravitational Wave Astrophysics,
the proceedings of the 2014 Sant Cugat Forum on Astrophysics; v2 includes one
additional referenc
The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
Observations indicate that nearly all galaxies contain supermassive black
holes (SMBHs) at their centers. When galaxies merge, their component black
holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves
(GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the
recently-released North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits.
As we did not find strong evidence for GWs in our data, we placed 95\% upper
limits on the strength of GWs from such sources as a function of GW frequency
and sky location. We placed a sky-averaged upper limit on the GW strain of at nHz. We also developed a
technique to determine the significance of a particular signal in each pulsar
using ``dropout' parameters as a way of identifying spurious signals in
measurements from individual pulsars. We used our upper limits on the GW strain
to place lower limits on the distances to individual SMBHBs. At the
most-sensitive sky location, we ruled out SMBHBs emitting GWs with
nHz within 120 Mpc for , and
within 5.5 Gpc for . We also determined that
there are no SMBHBs with emitting
GWs in the Virgo Cluster. Finally, we estimated the number of potentially
detectable sources given our current strain upper limits based on galaxies in
Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris
cosmological simulation project. Only 34 out of 75,000 realizations of the
local Universe contained a detectable source, from which we concluded it was
unsurprising that we did not detect any individual sources given our current
sensitivity to GWs.Comment: 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send
any comments/questions to S. J. Vigeland ([email protected]
Compact Binary Coalescences in the Band of Ground-based Gravitational-Wave Detectors
As the ground-based gravitational-wave telescopes LIGO, Virgo, and GEO 600
approach the era of first detections, we review the current knowledge of the
coalescence rates and the mass and spin distributions of merging neutron-star
and black-hole binaries. We emphasize the bi-directional connection between
gravitational-wave astronomy and conventional astrophysics. Astrophysical input
will make possible informed decisions about optimal detector configurations and
search techniques. Meanwhile, rate upper limits, detected merger rates, and the
distribution of masses and spins measured by gravitational-wave searches will
constrain astrophysical parameters through comparisons with astrophysical
models. Future developments necessary to the success of gravitational-wave
astronomy are discussed.Comment: Replaced with version accepted by CQG
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
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