Radio Observations And Modeling Of A Post-flare Arcade
Hazel Bain1,2, Lyndsay Fletcher2
(1) Space Sciences LaboratoryUC Berkeley
(2) Department of Physics and AstronomyUniversity of Glasgow
Event Overview
• Goes X3.1 class flare on the 24th August 2002.
• Radio observations show 6 impulsive radio bursts.
• RHESSI shows increased flux at 50 -100 keV just before night, 00:56.
• SONG detector onboard CORONAS-F shows correlation between HXR (64-180 keV and 180-600 keV) and radio. 6s at 17 GHz, 8s at 34 GHz (Reznikova 09).
• Associated prominence eruption/CME at 00:55.
TRACE and NoRH observations
• 00:45 – 00:56 : coronal loops move outwards (a - c).
• 00:59 – 01:10 : arcade forms from west to east i.e. right to left (d - g).
• 01:24: radio emission cospatial with TRACE hot diffuse source ~107 K (h - o).
• 01:24 – onwards: TRACE arcade forms at greater heights (h - o).
• Second radio loop appears. 01:24 34 GHz, 01:26 17GHz (h)
17 GHz 34 GHz
RHESSI6 – 12 keV (blue) 12 – 25 keV (green) 25 – 50 keV (red)
01:34
T1 = 16 MK, EM1 = 2 x 1049 cm-3
T2 = 30 MK, EM2 = 1 x 1048 cm-3
γ = 4
02:20
T1 = 12 MK, EM1 = 5 x 1049 cm-3
T2 = 18 MK, EM2 = 1 x 1048 cm-3
n = 5 x 109 – 1 x 1010 cm-3
Decay phase
NoRH 34 GHz (redscale)
17 GHz (contours)
-20-70-120
Brightness temperature, Tb (K) vs θ
Plasma parameters
Bightness temperature (K)
Radio spectral index
Electron spectral index
Nonthermal electron density N (cm-3).
(Dulk & Marsh 82)
Radio Model
• Melnikov 05, Tzatzakis 06, Reznikova 09 model impulsive radio bursts using Fokker-Planck approach.
• Consider only a simple dipole loop.
• Don’t consider thermal effects.
Our model
• Dipole vs arcade magnetic field models.
• Radio emission calculated for individual voxels – GS code by Dr Gregory Fleishman (Fleishman et al 09, Nita et al 09).
• Code uses Petrosian-Klein approximation (Petrosian 81).
• Vary input parameters for individual voxels and rotate viewing angle
• Radiative transfer along line of sight.
Nonthermal Gyrosynchrotron (Dipole)
• Gaussian distribution of nonthermal electrons centred at the looptop.
• Ratio of NLT:NFP ~ 1 order of magnitude to get both sources.
• δ decreases, ratio decreases.
Nonthermal Gyrosynchrotron (Arcade)
Line profile along loop (green line)
BLT = 150 G, BFP = 800 G
N = 104 cm-3, δ = 3
Input parameters are constant along loop
Thermal/Nonthermal Model
•Continuous function.
•Thermal and nonthermal components matched at critical point parameterised by ε.
Thermal/Nonthermal Model
Thermal/Nonthermal
Nonthermal Gyrosynchroton
Thermal Gyrosynchrotron component used for TNT model
Thermal/Nonthermal Model
Black
Red
Blue
Summary
Two or three promising models…
• For a dipole magnetic field model, an enhancement of nonthermal electrons is required at the looptop to produce both looptop and footpoint emission.
• An arcade model increases the line of sight distance at the looptop, resulting in enhanced emission without the need for an increase in NLT.
• However neither of these models are able to reproduce the steeper spectrum observed at the footpoints.
• For high temperature and strong B the thermal component can become important and dominate over the nonthermal GS spectrum leading to a steeper spectrum at the footpoints.
• However the addition of a thermal component results in absorption at lower frequencies and does not match the observed NoRP flux.
