Multi-messenger astronomy of gravitational-wave sources with flexible wide-area radio transient surveys

We explore opportunities for multi-messenger astronomy using gravitational waves (GWs) and prompt, transient low-frequency radio emission to study highly energetic astrophysical events. We review the literature on possible sources of correlated emission of gravitational waves and radio transients, highlighting proposed mechanisms that lead to a short-duration, high-flux radio pulse originating from the merger of two neutron stars or from a superconducting cosmic string cusp. We discuss the detection prospects for each of these mechanisms by low-frequency dipole array instruments such as LWA1, LOFAR and MWA. We find that a broad range of models may be tested by searching for radio pulses that, when de-dispersed, are temporally and spatially coincident with a LIGO/Virgo GW trigger within a \usim 30 second time window and \usim 200 \mendash 500 \punits{deg}^{2} sky region. We consider various possible observing strategies and discuss their advantages and disadvantages. Uniquely, for low-frequency radio arrays, dispersion can delay the radio pulse until after low-latency GW data analysis has identified and reported an event candidate, enabling a \emph{prompt} radio signal to be captured by a deliberately targeted beam. If neutron star mergers do have detectable prompt radio emissions, a coincident search with the GW detector network and low-frequency radio arrays could increase the LIGO/Virgo effective search volume by up to a factor of \usim 2. For some models, we also map the parameter space that may be constrained by non-detections.Comment: 31 pages, 4 figure

Observations of Giant Pulses from Pulsar PSR B0950+08 using LWA1

We report the detection of giant pulse emission from PSR B0950+08 in 24 hours of observations made at 39.4 MHz, with a bandwidth of 16 MHz, using the first station of the Long Wavelength Array, LWA1. We detected 119 giant pulses from PSR B0950+08 (at its dispersion measure), which we define as having SNRs at least 10 times larger than for the mean pulse in our data set. These 119 pulses are 0.035% of the total number of pulse periods in the 24 hours of observations. The rate of giant pulses is about 5.0 per hour. The cumulative distribution of pulse strength $S$ is a steep power law, $N(>S)\propto S^{-4.7}$, but much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a dispersion measure range from 1 to 90 pc cm$^{-3}$, in the beam tracking PSR B0950+08. The giant pulses have a narrower temporal width than the mean pulse (17.8 ms, on average, vs. 30.5 ms). The pulse widths are consistent with a previously observed weak dependence on observing frequency, which may be indicative of a deviation from a Kolmogorov spectrum of electron density irregularities along the line of sight. The rate and strength of these giant pulses is less than has been observed at $\sim$100 MHz. Additionally, the mean (normal) pulse flux density we observed is less than at $\sim$100 MHz. These results suggest this pulsar is weaker and produces less frequent giant pulses at 39 MHz than at 100 MHz.Comment: 27 pages, 12 figures, typos correcte

Observations of Giant Pulses from Pulsar B0950+08 Using LWA1

We report the detection of giant pulse (GP) emission from PSR B0950+08 in 24 hours of observations made at 39.4 MHz, with a bandwidth of 16 MHz, using the first station of the Long Wavelength Array. We detected 119 GPs from PSR B0950+08 (at its dispersion measure (DM)), which we define as having a signal-to-noise ratio at least 10 times larger than for the mean pulse in our data set. These 119 pulses are 0.035% of the total number of pulse periods in the 24 hours of observations. The rate of GPs is about 5.0 per hour. The cumulative distribution of pulse strength S is a steep power law, _N(>S) ∝ S^(-4.7), but much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a DM range from 1 to 90 pc cm^(−3), in the beam tracking PSR B0950+08. The GPs have a narrower temporal width than the mean pulse (17.8 ms, on average, versus 30.5 ms). The pulse widths are consistent with a previously observed weak dependence on observing frequency, which may be indicative of a deviation from a Kolmogorov spectrum of electron density irregularities along the line of sight. The rate and strength of these GPs is less than has been observed at ~100 MHz. Additionally, the mean (normal) pulse flux density we observed is less than at ~100 MHz. These results suggest this pulsar is weaker and produces less frequent GPs at 39 MHz than at 100 MHz

Context-Dependent Encoding of Fear and Extinction Memories in a Large-Scale Network Model of the Basal Amygdala

The basal nucleus of the amygdala (BA) is involved in the formation of context-dependent conditioned fear and extinction memories. To understand the underlying neural mechanisms we developed a large-scale neuron network model of the BA, composed of excitatory and inhibitory leaky-integrate-and-fire neurons. Excitatory BA neurons received conditioned stimulus (CS)-related input from the adjacent lateral nucleus (LA) and contextual input from the hippocampus or medial prefrontal cortex (mPFC). We implemented a plasticity mechanism according to which CS and contextual synapses were potentiated if CS and contextual inputs temporally coincided on the afferents of the excitatory neurons. Our simulations revealed a differential recruitment of two distinct subpopulations of BA neurons during conditioning and extinction, mimicking the activation of experimentally observed cell populations. We propose that these two subgroups encode contextual specificity of fear and extinction memories, respectively. Mutual competition between them, mediated by feedback inhibition and driven by contextual inputs, regulates the activity in the central amygdala (CEA) thereby controlling amygdala output and fear behavior. The model makes multiple testable predictions that may advance our understanding of fear and extinction memories

Trends in Attitudes to and the Use of HIV Pre-exposure Prophylaxis by Australian Gay and Bisexual Men, 2011–2017: Implications for Further Implementation from a Diffusion of Innovations Perspective

Using repeated, national, online, cross-sectional surveys of Australian gay and bisexual men (GBM), we analysed trends related to HIV pre-exposure prophylaxis (PrEP). Specifically, we analysed trends in PrEP use, willingness to use PrEP, and concern about using PrEP during 2011–2017. We assessed support for GBM using PrEP and willingness to have sex with men taking PrEP between 2015 and 2017. For time-based analyses, we used multivariate logistic regression, controlling for sampling variations over time. We constructed new scales assessing reduced concern about HIV among PrEP users and non-users in 2017, and used multivariate logistic regression to identify independent correlates of PrEP use (vs. non-use). The analyses included 4567 HIV-negative and untested participants (2011–2017). PrEP use increased from 0.5% in 2011 to 25.5% in 2017 (p < 0.001). Willingness to use PrEP increased from 27.9% in 2011 to 36.5% in 2017 (p < 0.001) while concern about using PrEP fell (52.1–36.1%, p < 0.001). Support for GBM using PrEP remained stable (52.5% in 2015, 51.9% in 2017, p = 0.62), and willingness to have sex with men taking PrEP increased from 34.9% in 2015 to 49.0% in 2017 (p < 0.001). In 2017, 22.8% of non-PrEP-users had reduced HIV concern because of PrEP, while 73.6% of PrEP users had reduced HIV concern and greater sexual pleasure because of PrEP. The analysis of PrEP users vs. non-users in 2017 indicated that PrEP users were more sexually active and reported higher risk sexual practices, were more likely to live in New South Wales and Victoria, and to be in full-time employment. They were also more likely to know HIV-positive people and other PrEP users. Diffusion of Innovations theory suggests that future PrEP users in Australia may be less adventurous and require greater reassurance about PrEP’s efficacy and legitimacy, to sustain rollout and address current disparities in uptake

Trends in Attitudes to and the Use of HIV Pre-exposure Prophylaxis by Australian Gay and Bisexual Men, 2011–2017 : Implications for Further Implementation from a Diffusion of Innovations Perspective

Using repeated, national, online, cross-sectional surveys of Australian gay and bisexual men (GBM), we analysed trends related to HIV pre-exposure prophylaxis (PrEP). Specifically, we analysed trends in PrEP use, willingness to use PrEP, and concern about using PrEP during 2011–2017. We assessed support for GBM using PrEP and willingness to have sex with men taking PrEP between 2015 and 2017. For time-based analyses, we used multivariate logistic regression, controlling for sampling variations over time. We constructed new scales assessing reduced concern about HIV among PrEP users and non-users in 2017, and used multivariate logistic regression to identify independent correlates of PrEP use (vs. non-use). The analyses included 4567 HIV-negative and untested participants (2011–2017). PrEP use increased from 0.5% in 2011 to 25.5% in 2017 (p < 0.001). Willingness to use PrEP increased from 27.9% in 2011 to 36.5% in 2017 (p < 0.001) while concern about using PrEP fell (52.1–36.1%, p < 0.001). Support for GBM using PrEP remained stable (52.5% in 2015, 51.9% in 2017, p = 0.62), and willingness to have sex with men taking PrEP increased from 34.9% in 2015 to 49.0% in 2017 (p < 0.001). In 2017, 22.8% of non-PrEP-users had reduced HIV concern because of PrEP, while 73.6% of PrEP users had reduced HIV concern and greater sexual pleasure because of PrEP. The analysis of PrEP users vs. non-users in 2017 indicated that PrEP users were more sexually active and reported higher risk sexual practices, were more likely to live in New South Wales and Victoria, and to be in full-time employment. They were also more likely to know HIV-positive people and other PrEP users. Diffusion of Innovations theory suggests that future PrEP users in Australia may be less adventurous and require greater reassurance about PrEP’s efficacy and legitimacy, to sustain rollout and address current disparities in uptake