Flat Optically Thick Microwave Spectra Observed by EOVSA

ORAL

Abstract

The aim of this research is to examine the spectral dynamics of the low frequency gyrosynchrotron emission in association to the burst source of a solar flare. Studies focusing on the low frequency characteristics of bursts are rare, mainly due to the previous lack of the combination of spectral and spatial resolution in observations. High-resolution spectra observed by newly upgraded Expanded Owens Valley Solar Array(EOVSA) in the frequency range of 2.5 to 18 GHz are presented. Out of 14 events analysed in this study, 6 bursts display 'flat' optically thick spectrum (spectral index αl < 1.0), in contrary to the expected slopes and predictions of a homogeneous source model. This flat spectrum in a few events is observed especially in the decay phase of the burst and moreover with a constant reduction of spectral slope over the duration of the burst. This feature of flat spectrum can be explained as the emission from a spatially inhomogeneous gyrosynchrotron source of the flare, which evolves with the burst time. Additionally, the decrease in the flux with decreasing frequency leading to low index value in the optically thick side can also be often due to the gyrosynchrotron absorption. The physical parameters with probable dependence supporting the flat spectrum are presented.

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Authors

  • Shaheda Begum Shaik

    New Jersey Inst of Technology

  • Debbie Andres

    Department of Applied Physics and Department of Physics, Columbia University, Istituto Italiano di Tecnologia, Graphene Labs, Italy, Department of Physics and Astronomy, Purdue University, Department of Electrical Engineering, Princeton University, Department of Applied Physics and Applied Mathematics, Columbia University, NJIT, New Jersey Inst of Technology, New Jersey Inst of Tech, New Jersey Institute of Technology, Center for Advanced Radiation Sources, University of Chicago, High Pressure Science and Technology Advanced Research, State University of New York at Stony Brook, Rutgers University, NIST, Brookhaven National Laboratory, University of Chicago, University of South Florida, ETH Zurich, Max Planck POSTECH/Korea Research Initiative, University of Virginia, Rutgers University - Camden, New Jersey Institute of technology, Shaanxi Normal University, Pohang Science and Technology University, Sungkyunkwan University, Northern Illinois University and Argonne National Laboratory, Beijing National Laboratory for Condensed Matter Physics , and Institute of Physics, Chinese Academy of Sciences, Rutgers U., Orsova Engineers, U.S. Naval Research Laboratory, Center for Space Science and Engineering Research, Virginia Tech, Virginia., Princeton University, NASA Goddard Space Flight Center, Villanova University, SOFIA/USRA, Jet Propulsion Laboratory, Hudson Regional Health Commision, Rutgers University, College of William & Mary, Department of Physics, Drexel University, Drexel University, Drexel Universty, University of Massachusetts Amherst, Pohang Institue of Science and Technology, Indiana University - Purdue University Indianapolis, Department of Physics, University of Maryland, Naval Research Laboratory, Towson Univ, Rice University, Independence Blue Cross Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, Department of Physics, Temple University, PulseTorr LLC, Department of Chemistry, West Chester University, Department of Physics, West Chester University, College of William and Mary Dept. of Physics, University of Virginia Dept. of Materials Science and Engineering, United States Naval Academy, Rutgers The State University of New Jersey, Univ of Maryland-College Park, Los Alamos National Laboratory, POSTECH, New Jersey Institute of Technology, Department of Electrical and Computer Engineering, HamSCI/ARRL, Virginia Tech, Rutgers University-Camden, University of Washington, Rutgers, The State University of New Jersey