Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Localization and broadband follow-up of the gravitational-wave transient GW150914

A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams

Homies with Aspirations and Positive Peer Network Ties: Associations with Reduced Frequent Substance Use among Gang-Affiliated Latino Youth

In marginalized urban neighborhoods across the USA, Latino youth are disproportionately represented among the growing number of youth gangs. Substance use among gang-involved youth poses both immediate and long-term health risks and can threaten educational engagement, future socioeconomic stability, and desistance. Conventional assessments of gang-affiliated youth and their peer network overlook the possibility that positive peer ties may exist and can foster health promoting behavior norms. Drawing on a positive deviance framework, in this study, we examine the relationship between positive peer network characteristics tied to post-secondary educational aspirations and frequent alcohol and marijuana use among Latino, gang-affiliated youth from a neighborhood in San Francisco. Using generalized estimating equations regression models across 72 peer network clusters (162 youth), we found that having close friends who plan to go to a 4-year college was associated with a lower odds of frequent marijuana and alcohol use (OR 0.27, p = 0.02; OR 0.29, p = 0.14, respectively) and that this association persisted when adjusting for risk characteristics (OR 0.19, p < 0.01; OR 0.25, p = 0.12). Public health can advance gang intervention efforts by identifying protective and risk factors associated with non-criminal health outcomes to inform participatory research approaches and asset-based interventions that contribute to building healthy communities

The Social Environment and Childbearing Expectations: Implications for Strength-Based Sexual Health Interventions for Latino Youth

In the United States, adolescent childbearing is disproportionately higher among Latino youth, a growing population facing substantial social exclusion. Exploring the relationship between the social environment and sexual health outcomes among Latino youth may offer insights into the development of novel interventions. In this study, Latino youth in partnerships were recruited from neighborhood venues in San Francisco and completed in-depth interviews. Youth reported a desire to complete higher education goals prior to starting a family to improve future opportunities and further personal development. Youth stated that social network members, family and partners, were supportive of their individual childbearing expectations. Social environment barriers tied to poverty, immigration status, and gang violence hindered educational attainment. Some differences were noted by gender and immigrant generation. Building on protective social ties and creating avenues in poor, urban neighborhoods for Latino youth to fully access educational opportunities may counter early childbearing and improve sexual health

Localization and broadband follow-up of the gravitational-wave transient GW150914

A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams