Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session K12: Astrophysics Data Analysis |
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Sponsoring Units: DAP Chair: Hao Zhou, Michigan Tech Room: 250DE |
Sunday, April 17, 2016 1:30PM - 1:42PM |
K12.00001: Development of a Matched Runs Method for VERITAS Andrew Flinders VERITAS is an array of four Imaging Air Cherenkov Telescopes located in southern Arizona. It has been successful in detecting Very High Energy (VHE) radiation from a variety of sources including pulsars, Pulsar Wind Nebulae, Blazars, and High Mass X-Ray Binary systems. Each of these detections been accomplished using either the standard Ring Background Method or the Reflected Region Method in order to determine the appropriate background for the source region. For highly extended sources (\textgreater 1 degree) these background estimation methods become unsuitable due to the possibility of source contamination in the background regions. A new method, called the matched background method, has been implemented for potentially highly extended sources observed by VERITAS. It provides and algorithm for identifying a suitable gamma-ray background estimation from a different field of view than the source region. By carefully matching cosmic-ray event rates between the source and the background sky observations, a suitable gamma-ray background matched data set can be identified. We will describe the matched background method and give examples of its use for several sources including the Crab Nebula and IC443. [Preview Abstract] |
Sunday, April 17, 2016 1:42PM - 1:54PM |
K12.00002: HAWC Energy Reconstruction via Neural Network Samuel Marinelli The High-Altitude Water-Cherenkov (HAWC) $\gamma$-ray observatory is located at 4100 m above sea level on the Sierra Negra mountain in the state of Puebla, Mexico. Its 300 water-filled tanks are instrumented with PMTs that detect Cherenkov light produced by charged particles in atmospheric air showers induced by TeV $\gamma$-rays. The detector became fully operational in March of 2015. With a 2-sr field of view and duty cycle exceeding 90\%, HAWC is a survey instrument sensitive to diverse $\gamma$-ray sources, including supernova remnants, pulsar wind nebulae, active galactic nuclei, and others. Particle-acceleration mechanisms at these sources can be inferred by studying their energy spectra, particularly at high energies. We have developed a technique for estimating primary-$\gamma$-ray energies using an artificial neural network (ANN). Input variables to the ANN are selected to characterize shower multiplicity in the detector, the fraction of the shower contained in the detector, and atmospheric attenuation of the shower. Monte Carlo simulations show that the new estimator has superior performance to the current estimator used in HAWC publications. [Preview Abstract] |
Sunday, April 17, 2016 1:54PM - 2:06PM |
K12.00003: On the energy estimation of gamma rays using a ground parameter Kelly Malone The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is a recently completed, second-generation experiment designed to observe TeV gamma rays and cosmic rays from air showers, located at an altitude of 4100m near Sierra Negra, Mexico. It consists of an array of 300 water Cherenkov detectors, each of which contain 4 PMTs. Due to its $\sim$ 2 sr field of view and $>$90$\%$ duty cycle, it is well suited to observe a variety of transient and extended sources, including diffuse emission from the galactic plane, AGN, gamma-ray bursts, and cosmic ray anisotropy. Measuring the energy spectra of sources from 100 GeV up to $\sim$100 TeV is essential to understand the nature of cosmic accelerators. I will present a method to reconstruct the energy of gamma rays on an event-by-event basis by determining the lateral distribution function and measuring the charge density at an optimum distance from the shower axis. This method improves upon the technique that assigns a mean energy value for all events of a given shower size. This is particularly important above 10 TeV where the typical shower size is comparable to the detector area. [Preview Abstract] |
Sunday, April 17, 2016 2:06PM - 2:18PM |
K12.00004: Percolation analysis for cosmic web with discrete points Jiajun Zhang, Dalong Cheng, Ming-Chung Chu Percolation analysis has long been used to quantify the connectivity of the cosmic web. Unlike most of the previous works using density field on grids, we have studied percolation analysis based on discrete points. Using a Friends-of-Friends (FoF) algorithm, we generate the S-bb relation, between the fractional mass of the largest connected group (S) and the FoF linking length (bb). We propose a new model, the Probability Cloud Cluster Expansion Theory (PCCET) to relate the S-bb relation with correlation functions. We show that the S-bb relation reflects a combination of all orders of correlation functions. We have studied the S-bb relation with simulation and find that the S-bb relation is robust against redshift distortion and incompleteness in observation. From the Bolshoi simulation, with Halo Abundance Matching (HAM), we have generated a mock galaxy catalogue. Good matching of the projected two-point correlation function with observation is confirmed. However, comparing the mock catalogue with the latest galaxy catalogue from SDSS DR12, we have found significant differences in their S-bb relations. This indicates that the mock catalogue cannot accurately recover higher order correlation functions than the two-point correlation function, which reveals the limit of HAM method. [Preview Abstract] |
Sunday, April 17, 2016 2:18PM - 2:30PM |
K12.00005: Discontinuous Galerkin Methods for the Two-Moment Model of Radiation Transport Eirik Endeve, Cory Hauck We are developing computational methods for simulation of radiation transport in astrophysical systems (e.g., neutrino transport in core-collapse supernovae). Here we consider the two-moment model of radiation transport, where the energy density $E$ and flux $\boldsymbol{F}$ --- angular moments of a phase space distribution function --- approximates the radiation field in a computationally tractable manner. We aim to develop multi-dimensional methods that are (i) high-order accurate for computational efficiency, and (ii) robust in the sense that the solution remains in the realizable set $R=\{ (E,\boldsymbol{F}) ~ | ~ E\ge0 ~ \mbox{and} ~ E-|\boldsymbol{F}|\ge0\}$ (i.e., $E$ and $\boldsymbol{F}$ are consistent with moments of an underlying distribution). Our approach is based on the Runge-Kutta discontinuous Galerkin method\footnote{Cockburn \& Shu 2001, J. Sci. Comput. {\bf 16}, 173-261}, which has many attractive properties, including high-order accuracy on a compact stencil. We present the physical model and numerical method, and show results from a multi-dimensional implementation. Tests show that the method is high-order accurate and strictly preserves realizability of the moments. [Preview Abstract] |
Sunday, April 17, 2016 2:30PM - 2:42PM |
K12.00006: Results of NSF Workshop on Open Access to Data for the Mathematical and Physical Sciences Michael Hildreth In November 2015, we organized the first in a two-workshop series sponsored by the NSF to gather feedback from the scientific communities of the Mathematical and Physical Sciences (MPS) Directorate on potential requirements for open access to scientific data. The result of the workshop series will be a report delivered to the NSF expressing the views of scientists on what sorts of data should be openly available, what other information besides data is required, and what infrastructure is necessary. The first workshop generated a preliminary report that is available at http://mpsopendata.crc.nd.edu. Broad discussion of these ideas and recommendations is necessary in order to provide the greatest possible feedback to NSF. This presentation will review the main recommendations and engage in a dialogue with the audience. [Preview Abstract] |
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