During their violent merger, two neutron stars can shed a few percent of their mass. As this ejecta expands, it collides with the surrounding interstellar gas, producing a slowly-fading radio flare ...that lasts for years. Radio flares uniquely probe the neutron star merger populations as many events from past decades could still be detectable. Nonetheless, no radio flare observation has been reported to date. Here we show that the radio transient FIRST J1419+3940, first observed in 1993 and still detectable, could have originated from a neutron star merger. We carry out numerical simulations of neutron star merger ejecta to demonstrate that the observed radio light curve is well reproduced by a merger model with astrophysically expected parameters. We examine the observed radio data, as well as the host galaxy, to find clues that could differentiate the transient's neutron star merger origin from the alternative explanation---the afterglow of an off-axis long gamma-ray burst. Near-future observations could find further evidence for the FIRST J1419+3940 radio transient's origin. We show that existing radio surveys likely already recorded multiple radio flares, informing us of the origin and properties of neutrons tar mergers and their role in the nucleosynthesis of the heaviest elements in the Universe.
We present a machine-learning approach for estimating galaxy cluster masses from Chandra mock images. We utilize a Convolutional Neural Network (CNN), a deep machine learning tool commonly used in ...image recognition tasks. The CNN is trained and tested on our sample of 7,896 Chandra X-ray mock observations, which are based on 329 massive clusters from the IllustrisTNG simulation. Our CNN learns from a low resolution spatial distribution of photon counts and does not use spectral information. Despite our simplifying assumption to neglect spectral information, the resulting mass values estimated by the CNN exhibit small bias in comparison to the true masses of the simulated clusters (-0.02 dex) and reproduce the cluster masses with low intrinsic scatter, 8% in our best fold and 12% averaging over all. In contrast, a more standard core-excised luminosity method achieves 15-18% scatter. We interpret the results with an approach inspired by Google DeepDream and find that the CNN ignores the central regions of clusters, which are known to have high scatter with mass.
The course developed in this article is in response to the common approach to analytical chemistry which resembles an abbreviated course for technicians: students are "black box" operators rather ...than students of chemistry.
On February 10, 1993 an Air Force F-16 dropped an INS/GPS modified GBU-15 from an altitude of 35000 ft and a down range distance of 88000 ft in adverse weather. The guided weapon impacted within 6 ...meters of the target, demonstrating the potential of INS/GPS technology to significantly improve air-to-surface munitions strategies and tactics. This landmark flight was successfully followed by 5 additional drops with varying altitudes, downrange distances and weather conditions. OCD was designated an Air Force high gear program, allowing streamlined acquisition and reporting procedures, in response to Operation Desert Storm experience highlighting the need for attacking high-value targets from high altitude in adverse weather. OCD met it's objective to build and demonstrate an INS/GPS weapon in an operationally representative environment. Results of the demonstration show there is low technical risk associated with development of INS/GPS munitions considered for the Joint Direct Attack Munitions (JDAM) program. This paper provides additional details on program objectives, system implementation, and test results. The focus of this paper is on the implementation and performance of the integrated INS/GPS navigation system.< >
The discharge patterns of single afferent fibers from rat pudendal nerve were studied as a function in temperature of the scrotal skin, an area known to function in temperature regulation. In a ...number of respects the population of temperature-sensitive afferents here differ from most previously described; 75% of temperature-sensitive afferents were also sensitive to mechanical stimulation. Of the 25% nonmechanosensitive units, half showed dynamic and static responses to cooling, while most of the remaining fibers gave only static discharges to warming. The most frequent thermal reaction of the mechanosensitive units was a dynamic-static cold response or a pure static warm response. However, fibers were also present with only dynamic or only static cold responses. Of the bimodal units, 20% had a dynamic cold response, but showed a minimal static discharge at intermediate temperatures (about 35 degrees C) and an increased discharge on both warming and cooling from that temperature. One unit had static and dynamic warm responses. Whereas a bursting discharge in the cold has previously been considered to be a distinguishing characteristic of specific cold receptors, in the pudendal afferents a bursting discharge on cooling or at low temperatures is common both in mechanosensitive and specific cold fibers. This observation and the identical discharge patterns and mechanisms underlying the thermosensitivity argue for the view that the mechanosensitive afferents participate in thermal sensation and/or regulation along with the specific temperature receptors. Hellon and Misra (7) have concluded that there is processing of thermal information from the scrotal skin at the level of the first synapse in the cord. However, in this study, we have found peripheral afferents which have most of the discharge properties that led Hellon and Misra to conclude that processing had occurred. The unusual characteristics of thermosensitive afferents of the pudendal nerve suggest that there is probably organ specificity of neuronal discharge properties.
The velocity function is a fundamental observable statistic of the galaxy population, similarly impor- tant as the luminosity function, but much more difficult to measure. In this work we present the ...first directly measured circular velocity function that is representative between 60 < v_circ < 320 km/s for galaxies of all morphological types at a given rotation velocity. For the low mass galaxy population (60 < v_circ < 170 km/s), we use the HIPASS velocity function. For the massive galaxy population (170 < v_circ < 320 km/s), we use stellar circular velocities from the Calar Alto Legacy Integral Field Area Survey (CALIFA). In earlier work we obtained the measurements of circular velocity at the 80% light radius for 226 galaxies and demonstrated that the CALIFA sample can produce volume- corrected galaxy distribution functions. The CALIFA velocity function includes homogeneous velocity measurements of both late and early-type rotation-supported galaxies and has the crucial advantage of not missing gas-poor massive ellipticals that HI surveys are blind to. We show that both velocity functions can be combined in a seamless manner, as their ranges of validity overlap. The resulting observed velocity function is compared to velocity functions derived from cosmological simulations of the z = 0 galaxy population. We find that dark matter-only simulations show a strong mismatch with the observed VF. Hydrodynamic simulations fare better, but still do not fully reproduce observations.
We present for the first time metallicity maps generated using data from the Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies (LIRGs) and discuss the abundance ...gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models which trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.
On February 10, 1993 an Air Force F-16 dropped an INS/GPS modified GBU-15 from an altitude of 35,000 feet and a downrange distance of 88,000 feet in adverse weather. The guided weapon impacted within ...6 meters of the target, demonstrating the potential of INS/GPS technology to significantly improve air-to-surface munitions strategies and tactics. This landmark flight was successfully followed by five additional drops with varying attitudes, downrange distances and weather conditions. OCD was designated an Air Force High Gear program, allowing streamlined acquisition and reporting procedures, in response to Operation Desert Storm experience highlighting the need for attacking high-value targets from high altitude in adverse weather. OCD met it's objective to build and demonstrate an INS/GPS weapon in an operationally representative environment. Results of the demonstration show there is low technical risk associated with development of INS/GPS munitions considered for the Joint Direct Attack Munitions (JDAM) program.< >
