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24 Oct 2001 A Cool, Dense Flare

24 Oct 2001 A Cool, Dense Flare. T. S. Bastian 1 , G. Fleishman 1,2 , D. E. Gary 3. 1 National Radio Astronomy Observatory 2 Ioffe Institute for Physics and Technology 3 New Jersey Institute of Technology, Owens Valley Solar Array. Radio Observations.

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24 Oct 2001 A Cool, Dense Flare

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  1. 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

  2. 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

  3. 24 October 2001 AR 9672

  4. 1998 June 13 Kundu et al. 2001

  5. 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

  6. Hudson & Ryan’s (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

  7. 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.

  8. = 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

  9. = 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

  10. = 3.5, E1 = 100 keV, E2 = 2.5 MeV, nrl = 5 x 106 cm-3 B=150 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

  11. 1 spectrum/ 2 sec 2-parameter fits via c2- minimization nrl, T B, q, nth, A, L, E1, E2, d fixed

  12. X 107 X 107

  13. 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)

  14. q=2 q=3 q=4

  15. Hamilton & Petrosian 1992

  16. Bastian et al 1998

  17. 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 • Eloop=8.8 f191/2 (keV) • These flares have Eloop=50-60 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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