Day 1599

Monday.  Tuesday.  

1907.08298
MaxiMask and MaxiTrack: two new tools for identifying contaminants in astronomical images using convolutional neural networks
Paillassa, Bertin, Bouy

In this work, we propose two convolutional neural network classifiers for detecting contaminants in astronomical images. Once trained, our classifiers are able to identify various contaminants such as cosmic rays, hot and bad pixels, persistence effects, satellite or plane trails, residual fringe patterns, nebulous features, saturated pixels, diffraction spikes and tracking errors in images, encompassing a broad range of ambient conditions such as seeing, image sampling, detector type, optics and stellar density. The first classifier, MaxiMask, performs semantic segmentation and generates bad pixel maps for each contaminant, based on the probability for each pixel to belong to a given contaminant class. The second classifier, MaxiTrack, classifies entire images and mosaics, by computing the probability for the focal plane to be affected by tracking errors. Training and testing data have been gathered from real data originating from various modern CCD and near-infrared cameras, augmented with image simulations. We quantify the performance of both classifiers and show that MaxiMask achieves state-of-the-art performance for the identification of cosmic ray hits. Thanks to a built-in Bayesian update mechanism both classifiers can be tuned to meet specific science goals in various observational contexts.

1907.08530

The Cherenkov Telescope Array

Mazin

The Cherenkov Telescope Array (CTA) is the next generation ground-based observatory for gamma-ray astronomy at very-high energies. It will be capable of detecting gamma rays in the energy range from 20 GeV to more than 300 TeV with unprecedented precision in energy and directional reconstruction. With more than 100 telescopes of three different types it will be located in the northern hemisphere at La Palma, Spain, and in the southern at Paranal, Chile. CTA will be one of the largest astronomical infrastructures in the world with open data access and it will address questions in astronomy, astrophysics and fundamental physics in the next decades. In this presentation we will focus on the status of the CTA construction, the status of the telescope prototypes and highlight some of the physics perspectives.

1907.08564

The glow of annihilating dark matter in Omega Centauri

Brown, et al

Dark matter (DM) is the most abundant material in the Universe, but has so far been detected only via its gravitational effects. Several theories suggest that pairs of DM particles can annihilate into a flash of light at gamma-ray wavelengths. While gamma-ray emission has been observed from environments where DM is expected to accumulate, such as the centre of our Galaxy, other high energy sources can create a contaminating astrophysical gamma-ray background, thus making DM detection difficult. In principle, dwarf galaxies around the Milky Way are a better place to look -- they contain a greater fraction of DM with no astrophysical gamma-ray background -- but they are too distant for gamma-rays to have been seen. A range of observational evidence suggests that Omega Centauri (omega Cen or NGC 5139), usually classified as the Milky Way's largest globular cluster, is really the core of a captured and stripped dwarf galaxy. Importantly, Omega Cen is ten times closer to us than known dwarfs. Here we show that not only does Omega Cen contain DM with density as high as compact dwarf galaxies, but also that it emits gamma-rays with an energy spectrum matching that expected from the annihilation of DM particles with mass 31$\pm$4 GeV (68\% confidence limit). No astrophysical sources have been found that would otherwise explain Omega Cen's gamma-ray emission, despite deep multi-wavelength searches. We anticipate our results to be the starting point for even deeper radio observations of Omega Cen. If multi-wavelength searches continue to find no astrophysical explanations, this pristine, nearby clump of DM will become the best place to study DM interactions through forces other than gravity.

1907.08638

Galaxy-lens determination of $H_0$: constraining density slope in the context of the mass sheet degeneracy

Gomer, Williams

Gravitational lensing offers a a competitive method to measure $H_0$ with the goal of 1% precision. A major obstacle comes in the form of lensing degeneracies, such as the mass sheet degeneracy (MSD), which make it possible for a family of density profiles to reproduce the same lensing observables but return different values of $H_0$. The modeling process artificially selects one choice from this family, potentially biasing the recovered value of $H_0$. The effect is more pronounced when the profile of a given lens is not perfectly described by the lens model, which will always be the case to some extent. To explore this, we quantify the bias and spread by creating quads from two-component mass models and fitting them with a power-law ellipse+shear model. We find that the bias does not correspond to the estimate one would calculate by transforming the profile into a power law near the image radius. We also emulate the effect of including stellar kinematics by performing fits where the slope is constrained to the true value over a range of radii. Constraining the slope to the true value near the image radius can introduce substantial bias (0-8% for our most realistic models). We conclude that lensing degeneracies manifest in a more complicated way than is assumed. If stellar kinematics incorrectly break the MSD, their inclusion may introduce more bias than their omission.

1907.08663

Application Usability Levels: a framework for tracking project product progress

Halford, et al

The space physics community continues to grow and become both more interdisciplinary and more intertwined with commercial and government operations. This has created a need for a framework to easily identify what projects can be used for specific applications and how close the tool is to routine autonomous or on-demand implementation and operation. We propose the Application Usability Level (AUL) framework and publicizing AULs to help the community quantify the progress of successful applications, metrics, and validation efforts. This framework will also aid the scientific community by supplying the type of information needed to build off of previously published work and publicizing the applications and requirements needed by the user communities. In this paper, we define the AUL framework, outline the milestones required for progression to higher AULs, and provide example projects utilizing the AUL framework. This work has been completed as part of the activities of the Assessment of Understanding and Quantifying Progress working group which is part of the International Forum for Space Weather Capabilities Assessment.