24 Oct 2001 A Cool, Dense Flare

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24 Oct 2001A Cool, Dense Flare

• T. S. Bastian1, G. Fleishman1,2, D. E. Gary3

1National Radio Astronomy Observatory 2Ioffe
Institute for Physics and Technology 3New Jersey
Institute of Technology, Owens Valley Solar Array
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Radio Observations
OVSA 1-14.8 GHz, 2 s cadence, total flux, Stokes
I NoRP 1, 2, 3.75, 9.4, 17, 35, and 80 GHz, 0.1
s cadence, total flux, Stokes I/V NoRH 17 GHz, 1
s cadence, imaging (10), Stokes I/V
34 GHz, 1 s cadence, imaging (5), Stokes I
EUV/X-ray Observations
TRACE 171 A imaging, 40 s cadence (0.5) Yohkoh
SXT Single Al/Mg full disk image (4.92) Yohkoh
HXT Counts detected in L band only
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24 October 2001
AR 9672
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1998 June 13
Kundu et al. 2001
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Observational Summary

• Impulsive, radio rich flare little EUV, SXR,
  HXR
• Low frequency cut-off below 10 GHz
• Flux maxima delayed with decreasing frequency
• Flux decay approx. frequency independent late in
  event

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Hudson Ryans (1995) Impulse response flares

• First pointed out by White et al (1992).
• Simple impulsive profile
• Flat spectrum
• Sharp low frequency cutoff
• No SXRs!

from White et al 1992
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Interpretation

• Radio emission is due to GS emission from
  non-thermal distribution of electrons in
  relatively cool, dense plasma
• Ambient plasma density is high therefore, Razin
  suppression is relevant
• Thermal free-free absorption is also important
  (n2T-3/2n-2)
• Include these ingredients in the source function
  (cf. Ramaty Petrosian 1972)
• The idea is that energy loss by fast electrons
  heats the ambient plasma, reducing the free-free
  opacity with time, thereby accounting for the
  reverse delay structure.

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• 3.5, E1 100 keV, E2 2.5 MeV, nrl 5 x
  106 cm-3
• nth 1011 cm-3, T 2 x 106 K, A 2 x 1018 cm2,
  L 9 x 108 cm

B 350
B 300
B 250
B 200
B 150
nth 0
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• 3.5, E1 100 keV, E2 2.5 MeV, nrl 5 x
  106 cm-3
• B 150 G, T 2 x 106 K, A 2 x 1018 cm2, L 9
  x 108 cm

nth 50 x 1010
nth 0
nth 20 x 1010
nth 10 x 1010
nth 5 x 1010
nth 2 x 1010
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• 3.5, E1 100 keV, E2 2.5 MeV, nrl 5 x
  106 cm-3
• B150 G, nth 1011 cm-3, A 2 x 1018 cm2, L 9
  x 108 cm

T 20 x 106
T 10 x 106
T 5 x 106
T 2 x 106
nth 0
T 1 x 106
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1 spectrum/ 2 sec
2-parameter fits via c2- minimization
nrl, T B, q, nth, A, L, E1, E2, d fixed
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X 107
X 107
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Essential features of the flare are adequately
described by the proposed scenario. An
outstanding issue that has not been addressed is
the fact that all frequencies appear to decay
with a similar time scale beyond the time of
spectral maximum. Possible explanations High
energy cutoff E2 discounted by spectral
fits Transport not determined by Coulomb
collisions Scattering by turbulence e.g.,
Whistlers (Hamilton Petrosian 1992), fast-mode
MHD waves (Miller et al. 1996)
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q2
q3
q4
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Hamilton Petrosian 1992
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Bastian et al 1998
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2002 April 14
Coronal thick-target flares
Veronig Brown 2004

• Two examples presented of gradual flares wherein
  the corona is collisionally thick.
• Electron distribution function, while steep (d
  6-7) is definitely non-thermal (NoRH)
• Column depth f 5 x 1020 cm-2
• Eloop8.8 f191/2 (keV)
• These flares have Eloop50-60 keV!
• The implied coronal density of thermal plasma is
  nth 2 x 1011 cm-3

Color-12 kev Contours 25-50 keV
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