skip to main content

Title: OPTICAL SPECTRAL OBSERVATIONS OF A FLICKERING WHITE-LIGHT KERNEL IN A C1 SOLAR FLARE

We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, ≤0.''5 (10{sup 15} cm{sup 2}) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a ''blue continuum bump'' in the excess emission which may be indicative ofmore » the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Goddard Space Flight Center, Code 671, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)
  2. INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy and National Solar Observatory, Sunspot NM (United States)
  3. SUPA School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom)
Publication Date:
OSTI Identifier:
22364630
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 798; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHROMOSPHERE; COMPUTERIZED SIMULATION; COSMIC GAMMA BURSTS; DETECTION; ELECTRON BEAMS; HARD X RADIATION; HYDROGEN; KERNELS; MAGNETIC RECONNECTION; OPACITY; PHOTOSPHERE; RESOLUTION; SOLAR FLARES; SPACE; SUN; TELESCOPES; VISIBLE RADIATION