389 research outputs found

    GW170817 Most Likely Made a Black Hole

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    There are two outstanding issues regarding the neutron-star merger event GW170817: the nature of the compact remnant and the interstellar shock. The mass of the remnant of GW170817, \sim2.7 MM_\odot, implies the remnant could be either a massive, rotating, neutron star, or a black hole. We report Chandra Director's Discretionary Time observations made in 2017 December and 2018 January, and we reanalyze earlier observations from 2017 August and 2017 September, in order to address these unresolved issues. We estimate the X-ray flux from a neutron star remnant and compare that to the measured X-ray flux. If we assume that the spin-down luminosity of any putative neutron star is converted to pulsar wind nebula X-ray emission in the 0.5-8 keV band with an efficiency of 10310^{-3}, for a dipole magnetic field with 3×10113 \times 10^{11} G < BB < 101410^{14} G, a rising X-ray signal would result and would be brighter than that observed by day 107, we therefore conclude that the remnant of GW170817 is most likely a black hole. Independent of any assumptions of X-ray efficiency, however, if the remnant is a rapidly-rotating, magnetized, neutron star, the total energy in the external shock should rise by a factor \sim10210^2 (to \sim105210^{52} erg) after a few years, therefore, Chandra observations over the next year or two that do not show substantial brightening will rule out such a remnant. The same observations can distinguish between two different models for the relativistic outflow, either an angular or radially varying structure.Comment: 10 pages, 4 figures, accepted to ApJ

    A calibration of the stellar mass fundamental plane at z ~ 0.5 using the micro-lensing induced flux ratio anomalies of macro-lensed quasars

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    We measure the stellar mass surface densities of early type galaxies by observing the micro-lensing of macro-lensed quasars caused by individual stars, including stellar remnants, brown dwarfs and red dwarfs too faint to produce photometric or spectroscopic signatures. Instead of observing multiple micro-lensing events in a single system, we combine single epoch X-ray snapshots of ten quadruple systems, and compare the measured relative magnifications for the images with those computed from macro-models. We use these to normalize a stellar mass fundamental plane constructed using a Salpeter IMF with a low mass cutoff of 0.1 solar mass and treat the zeropoint of the surface mass density as a free parameter. Our method measures the graininess of the gravitational potential produced by individual stars, in contrast to methods that decompose a smooth total gravitational potential into two smooth components, one stellar and one dark. We find the median likelihood value for the normalization factor F by which the Salpeter stellar masses must be multiplied is 1.23, with a one sigma confidence range, dominated by small number statistics, of 0.77 < F < 2.10Comment: Revised in response to referee's suggestions and re-submitted to ApJ; changes to the adopted effective radii propagate to a new value of the factor F (by which Salpeter stellar masses must be multiplied) of 1.2

    National security: A propositional study to develop resilience indicators as an aid to personnel vetting

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    Within the National Security domain there is a convergence of security responsibility across the national security agencies, law enforcement and private security sectors. The sensitivity of this environment requires individuals operating in the domain to be honest, trustworthy and loyal. Personnel vetting is a formal process used to determine an individual’s suitability for access to this domain. Notwithstanding this process, significant breaches of trust, security, and corruption still occur. In psychology, resilience is a well researched phenomenon that is considered a multidimensional construct where individual attributes, family aspects and social environment interact in aiding individuals to deal with vulnerability. There are many understandings and definitions of resilience based on theorists’ different perspectives; however, most agree that resilience is represented by a minimum of two aspects. The first is adversity and second, how the individual deals with adversity that demonstrates situational adaptation in a positive manner. The study is a work in progress and proposes the use of a recently developed Lifespan Resilience Scale. This scale will use resilience markers as an aid to National Security by providing vetting agencies with an additional tool for proactive intervention. The Lifespan Resilience Scale is currently undergoing reliability and validity testing within a student population. Once validated within this population, the scale will be adjusted and tested within the vetting environment using cross validated cohorts and expert opinion. Such a tool will assist National Security through better personnel risk management

    X-ray and Optical Study of Low Core Density Globular Clusters NGC6144 and E3

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    We report on the Chandra X-ray Observatory and Hubble Space Telescope observation of two low core density globular clusters, NGC6144 and E3. By comparing the number of X-ray sources inside the half-mass radius to those outside, we found 6 X-ray sources within the half-mass radius of NGC6144, among which 4 are expected to be background sources; 3 X-ray sources are also found within the half-mass radius of E3, of which 3 is expected to be background source. Therefore, we cannot exclude that all our sources are background sources. However, combining the results from X-ray and optical observations, we found that 1-2 sources in NGC6144 and 1 source in E3 are likely to be cataclysmic variables and that 1 source in NGC6144 is an active binary, based on the X-ray and optical properties. The number of faint X-ray sources in NGC6144 and E3 found with Chandra and HST is higher than a prediction based on collision frequency, but is closer to that based on mass. Our observations strongly suggest that the compact binary systems in NGC6144 and E3 are primordial in origin.Comment: 28 pages, 9 figures, 6 tables, Accepted for publication in Ap