Search for Eccentric Binary Neutron Star Mergers in the first and second observing runs of Advanced LIGO

We present a search for gravitational waves from merging binary neutron stars which have non-negligible eccentricity as they enter the LIGO observing band. We use the public Advanced LIGO data which covers the period from 2015 through 2017 and contains $\sim164$ days of LIGO-Hanford and LIGO-Livingston coincident observing time. The search was conducted using matched-filtering using the PyCBC toolkit. We find no significant binary neutron star candidates beyond GW170817, which has previously been reported by searches for binaries in circular orbits. We place a 90% upper limit of $\sim1700$ mergers $\textrm{Gpc}^{-3} \textrm{Yr}^{-1}$ for eccentricities $\lesssim 0.43$ at a dominant-mode gravitational-wave frequency of 10 Hz. The absence of a detection with these data is consistent with theoretical predictions of eccentric binary neutron star merger rates. Using our measured rate we estimate the sensitive volume of future gravitational-wave detectors and compare this to theoretical rate predictions. We find that, in the absence of a prior detection, the rate limits set by six months of Cosmic Explorer observations would constrain all current plausible models of eccentric binary neutron star formation

Dynamic Normalization for Compact Binary Coalescence Searches in Non-Stationary Noise

The output of gravitational-wave interferometers, such as LIGO and Virgo, can be highly non-stationary. Broadband detector noise can affect the detector sensitivity on the order of tens of seconds. Gravitational-wave transient searches, such as those for colliding black holes, estimate this noise in order to identify gravitational-wave events. During times of non-stationarity we see a higher rate of false events being reported. To accurately separate signal from noise, it is imperative to incorporate the changing detector state into gravitational-wave searches. We develop a new statistic which estimates the variation of the interferometric detector noise. We use this statistic to re-rank candidate events identified during LIGO-Virgo's second observing run by the PyCBC search pipeline. This results in a 7% improvement in the sensitivity volume for low mass binaries, particularly binary neutron stars mergers

Tracking Route Progression in the Posterior Parietal Cortex

SummaryQuick and efficient traversal of learned routes is critical to the survival of many animals. Routes can be defined by both the ordering of navigational epochs, such as continued forward motion or execution of a turn, and the distances separating them. The neural substrates conferring the ability to fluidly traverse complex routes are not well understood, but likely entail interactions between frontal, parietal, and rhinal cortices and the hippocampus. This paper demonstrates that posterior parietal cortical neurons map both individual and multiple navigational epochs with respect to their order in a route. In direct contrast to spatial firing patterns of hippocampal neurons, parietal neurons discharged in a place- and direction-independent fashion. Parietal route maps were scalable and versatile in that they were independent of the size and spatial configuration of navigational epochs. The results provide a framework in which to consider parietal function in spatial cognition

From One to Many: A Deep Learning Coincident Gravitational-Wave Search

Gravitational waves from the coalescence of compact-binary sources are now routinely observed by Earth bound detectors. The most sensitive search algorithms convolve many different pre-calculated gravitational waveforms with the detector data and look for coincident matches between different detectors. Machine learning is being explored as an alternative approach to building a search algorithm that has the prospect to reduce computational costs and target more complex signals. In this work we construct a two-detector search for gravitational waves from binary black hole mergers using neural networks trained on non-spinning binary black hole data from a single detector. The network is applied to the data from both observatories independently and we check for events coincident in time between the two. This enables the efficient analysis of large quantities of background data by time-shifting the independent detector data. We find that while for a single detector the network retains $91.5\%$ of the sensitivity matched filtering can achieve, this number drops to $83.9\%$ for two observatories. To enable the network to check for signal consistency in the detectors, we then construct a set of simple networks that operate directly on data from both detectors. We find that none of these simple two-detector networks are capable of improving the sensitivity over applying networks individually to the data from the detectors and searching for time coincidences

Prospects for detecting gravitational waves from eccentric subsolar mass compact binaries

Sub-solar mass black hole binaries, due to their light mass, would have to be primordial in origin instead of the result of stellar evolution. Soon after formation in the early Universe, primordial black holes can form binaries after decoupling from the cosmic expansion. Alternatively, primordial black holes as dark matter could also form binaries in the late Universe due to dynamical encounters and gravitational-wave braking. A significant feature for this channel is the possibility that some sources retain non-zero eccentricity in the LIGO/Virgo band. Assuming all dark matter is primordial black holes with a delta function mass distribution, $1M_\odot-1M_\odot$ binaries formed in this late Universe channel can be detected by Advanced LIGO and Virgo with at their design sensitivities with a rate of $\mathcal{O}(1)$/year, where $12\%(3\%)$ events have eccentricity at gravitational-wave frequency 10 Hz, $e^\mathrm{10Hz}\geq0.01(0.1)$, and non-detection can constrain the binary formation rate within this model. Third generation detectors would be expected to detect sub-solar mass eccentric binaries as light as $0.01 M_\odot$ within this channel, if they account for the majority of the dark matter. Furthermore, we use simulated gravitational-wave data to study the ability to search for eccentric gravitational-wave signals using quasi-circular waveform template bank with Advanced LIGO design sensitivity. Assuming binaries with a delta function mass of $0.1(1)M_\odot$ and the eccentricity distribution derived from this late Universe formation channel, for a match-filtering targeted search, $41\%(6\%)$ of the signals would be missed compared to ideal detection rate due to the mismatch in the gravitational-wave signal from eccentricity

Broad search for gravitational waves from subsolar-mass binaries through LIGO and Virgo's third observing run

We present a search for gravitational waves from the coalescence of binaries which contain at least one subsolar mass component using data from the LIGO and Virgo observatories through the completion of their third observing run. The observation of a merger with a component below $1\,M_{\odot}$ would be a clear sign of either new physics or the existence of a primordial black hole population; these black holes could also contribute to the dark matter distribution. Our search targets binaries where the primary has mass $M_1$ between 0.1-100$\,M_{\odot}$ and the secondary has mass $M_2$ from 0.1-1$\,M_{\odot}$ for $M_1 0.5\,M_\odot$ are also allowed to have orbital eccentricity up to $e_{10} \sim 0.3$. This search region covers from comparable to extreme mass ratio sources up to $10^4:1$. We find no statistically convincing candidates and so place new upper limits on the rate of mergers; our analysis sets the first limits for most subsolar sources with $7\,M_{\odot} 20\,M_{\odot}$ ($M_1 < 7\,M_{\odot}$). Using these limits, we constrain the dark matter fraction to below 0.3 (0.7)$\%$ for 1 (0.5)$\,M_{\odot}$ black holes assuming a monochromatic mass function. Due to the high merger rate of primordial black holes beyond the individual source horizon distance, we also use the lack of an observed stochastic background as a complementary probe to limit the dark matter fraction. We find that although the limits are in general weaker than those from the direct search they become comparable at $0.1 \,M_{\odot}$

Investigating the noise residuals around the gravitational wave event GW150914

We use the Pearson cross-correlation statistic proposed by Liu and Jackson, and employed by Creswell et al., to look for statistically significant correlations between the LIGO Hanford and Livingston detectors at the time of the binary black hole merger GW150914. We compute this statistic for the calibrated strain data released by LIGO, using both the residuals provided by LIGO and using our own subtraction of a maximum-likelihood waveform that is constructed to model binary black hole mergers in general relativity. To assign a significance to the values obtained, we calculate the cross-correlation of both simulated Gaussian noise and data from the LIGO detectors at times during which no detection of gravitational waves has been claimed. We find that after subtracting the maximum likelihood waveform there are no statistically significant correlations between the residuals of the two detectors at the time of GW150914.Comment: 14 pages, 7 figures. Minor text and figure changes in final v3. Notebooks for generating the results are available at https://github.com/gwastro/gw150914_investigatio

Sensitivity of spin-aligned searches for neutron star-black hole systems using future detectors

Current searches for gravitational waves from compact-binary objects are primarily designed to detect the dominant gravitational-wave mode and assume that the binary components have spins which are aligned with the orbital angular momentum. These choices lead to observational biases in the observed distribution of sources. Sources with significant spin-orbit precession or unequal-mass-ratios, which have non-negligible contributions from sub-dominant gravitational-wave modes, may be missed; in particular, this may significantly suppress or bias the observed neutron star -- black hole (NSBH) population. We simulate a fiducial population of NSBH mergers and determine the impact of using searches that only account for the dominant-mode and aligned spin. We compare the impact for the Advanced LIGO design, A+, LIGO Voyager, and Cosmic Explorer observatories. We find that for a fiducial population where the spin distribution is isotropic in orientation and uniform in magnitude, we will miss $\sim 25\%$ of sources with mass-ratio $q > 6$ and up to $\sim 60 \%$ of highly precessing sources $(\chi_p > 0.5)$, after accounting for the approximate increase in background. In practice, the true observational bias can be even larger due to strict signal-consistency tests applied in searches. The observation of low spin, unequal-mass-ratio sources by Advanced LIGO design and Advanced Virgo may in part be due to these selection effects. The development of a search sensitive to high mass-ratio, precessing sources may allow the detection of new binaries whose spin properties would provide key insights into the formation and astrophysics of compact objects