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

A next-generation liquid xenon observatory for dark matter and neutrino physics

The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector

Dimensional weighting of primary and secondary target-defining dimensions in visual search for singleton conjunction targets

Two experiments investigated dimension-based attentional processing in a complex singleton conjunction search task. In Experiment 1, observers had to discern the presence of a singleton target defined by a conjunction of size (fixed primary dimension) with either color or motion direction (secondary dimension). Similar to findings in singleton feature search, changes (vs. repetitions) of the secondary dimension across trials resulted in reaction time (RT) costs—which were, however, increased by a factor of 3–5 compared to singleton feature search. In Experiment 2, the coding of search-critical, dimensional saliency signals was investigated by additionally presenting targets redundantly defined in both secondary dimensions, with redundant-target signals being either spatially coincident or separate (i.e., one vs. two target items). Redundant-target RTs significantly violated Miller’s (Cognit Psychol 14:247–279, 1982) race model inequality only when redundant signals were spatially coincident (i.e., bound to a single object), indicating coactive processing of target information in the two secondary dimensions. These findings suggest that the coding and combining of signals from different visual dimensions operates in parallel. Increased change costs in singleton conjunction search are likely to reflect a reduced amount of weight available for processing the secondary target-defining dimensions, due to a large amount of weight being bound by the primary dimension