Paper Title:
High resolution observations of muti-wavelength emissions during two
x-class white-light flares

Author List:
Yan Xu, Wenda Cao, Chang Liu, Guo Yang, Ju Jing, Carsten Denker and
Haimin Wang

Abstract:
  We observed two X-class white-light flares on 2003 October 29
  ($\sim$ 2040 UT) and November 2 ($\sim$ 1716 UT) using the Dunn
  Solar Telescope (DST) and its High-order Adaptive Optics System
  (HAO) in several wavelengths. The spatial resolution was close to
  the diffraction limit of DST's 76~cm aperture. The temporal
  resolution was up to 2~seconds. A preliminary study of the NIR
  emission of the October 29 event was presented in \citet{Xu2004}.
  We extended the study in this paper by comparing the photospheric
  continuum observations during two events with corresponding
  line-of-sight magnetograms of the Michelson Doppler Imager (MDI),
  hard X-ray (HXR) data of \emph{RHESSI}. Significant emissions were
  shown both in visible, near-infrared (NIR) continua and G-band
  during the impulsive phase of the flares. The maximum intensity
  enhancements were 37\% of white-light, 25\% of the NIR continuum
  during the first event and 65\% of white-light, 66\% of the NIR
  continuum for the second flare. The flares were typical two ribbon
  flares. All the ribbons showed the same intensity distribution, a
  brighter core surrounded by a halo structure. The ribbon
  separation speeds were about 28~km/s in the first event and
  20~km/s of the second based on the NIR data. The derived electric
  field in reconnection current sheet $E_{c}$ were about $45~V
  cm^{-1}$ and $20~V cm^{-1}$ during the flare maxima, respectively.
  A good temporal relationship was observed between the two continua
  emission and impulsive HXR with energy range up to 800~keV.
  Besides, a small delay less than 2 minutes was shown between HXR
  and the continua. In addition, the high resolution images gave us
  the first chance to measure the cooling time of flaring areas
  close to the photosphere. We found that the cooling process could
  be characterize into two steps, a quick drop which should be
  related the major cooling process and a relative slow flattening
  caused by the halo structures. The quick step is about 30~second
  or less and few minutes in the second step. Based on the
  observational results, we discussed processes and conclusions of
  several models that provide possible mechanisms causing those
  continuum emissions, especially in the NIR.

Poster:
No