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Date: Wednesday, April 19, 2023
Speaker: Dr. Nat Gopalswamy, NASA Goddard Space Flight Center, Greenbelt, MD 20771, Astrophysicist, Solar Physics Laboratory, Heliophysics Science Division
Title: Coronal Mass Ejections and Solar Gamma-ray Emission
Time: 1:00 p.m. EDT
Abstract: Sustained gamma-ray emission (SGRE) from the Sun is characterized by a time-extended emission well beyond the impulsive phase of solar flares. SGRE was first identified by Forrest et al. (1985) using data from the Solar Maximum Mission’s Gamma-Ray Spectrometer. Only a handful of SGRE events were known over the next thirty years until the advent of the Fermi satellite’s Large Area Telescope (LAT). Fermi/LAT has detected more than three-dozen of these events, which help us obtain their statistical properties and their association with solar eruptive events. These events help us understand the origin of >300 MeV protons that interact with the solar chromosphere, produce neutral pions, which decay into the observed gamma-rays. SGRE events are associated with solar flares of X-ray class M and X, large solar energetic particle (SEP) events, interplanetary type II radio bursts, and superfast (>2000 km/s) coronal mass ejections (CMEs). All these eruptive phenomena are related to one another. Energetic CMEs drive shocks that accelerate protons observed as SEPs and electrons resulting in type II bursts. Particles are also accelerated in the flare reconnection region, which is spatially compact. The flare particles are responsible for various impulsive phase emissions including gamma-rays, which have properties different from those of SGREs. Some authors attribute even SGREs to flare-accelerated protons trapped in flare loops, although their close connection to SEPs, type II bursts, and CMEs point to an extended source, viz., the shock driven by CMEs. In this talk, I will review the properties of SGRE events and the associated phenomenon and the current understanding of this elusive energetic phenomenon.
Biography: He is an Astrophysicist at NASA’s Goddard Space Flight Center, Solar Physics Laboratory, Heliophysics Science Division. His research is in the area of solar and solar terrestrial physics including coronal mass ejections, solar flares, solar energetic particles, solar radio bursts, interplanetary shocks, and space weather. He is a Co-Investigator of the Solar Terrestrial Relations Observatory (STEREO) mission and the Principal Investigator of the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE). He directs the Coordinated Data Analysis Workshop (CDAW) Data Center that provides data on solar eruptions since 1996. He has authored or co-authored more than 475 scientific articles and has edited nine books, is the Executive Director of the International Space Weather Initiative (ISWI), Past President of the Scientific Committee on Solar Terrestrial Physics (SCOSTEP), and Vice Chair of COSPAR's panel on Space Weather. His awards include the 2013 NASA Leadership Medal, 2017 John C. Lindsay Memorial Award for Space Science, and American Geophysical Union’s Space Physics & Aeronomy Richard Carrington (SPARC) Award (2019). He was conferred with a Doctor Honoris Causa by the Bulgarian Academy of Sciences (2019) and is a Fellow of the American Geophysical Union and the International Science Council. He received his PhD (Physics) from the Indian Institute of Science (1982) and postdoctoral training (radio astronomy) at the University of Maryland at College Park (1985).
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