RHESSI Paris 27-Jul-04

Microflares (joint session of WG3 and WG4)

Christe: RHESSI microflare observations
 * "RHESSI is good at seeing small things"
 * survey of 5-sigma enhancements in two 3-4 day time intervals, chosen
  for low activity (GOES A0.01-C events, flaring rate 2.5/h)
Discussion of Fe features (Hudson, Grigis, Caspi) - even at night background?
 * 8-13/13-20 keV channel ratio to compare with Lin et al. 2001; peak 
  time from 3-12 keV rate. Background from hand-selected pre-event time.
  Time scales 4 s - 3 min accepted. 
 * spectral ratio interpreted either as powerlaw or kT
 * 4-7/7-10 => T near 10 MK; if non-thermal then gamma peaks at 6 keV
 * conclusions: T/NT transition between 7-13 keV? Smaller events problematic;
  energies 10^27 ergs for the smallest events  
Discussion (Grigis) about distribution function

Hannah: RHESSI microflare observations
 * sophisticated fitting and statistics
 * channel-ratio parameter estimation for simplicity; pre-event 
  background manually selected, all A0 of course
 * 26-jun-02 17:18 example  
 * ratio vs OSPEX model. Residuals are similar but show a large swing at
  6 keV in each case, and a systematic effect due to T underestimation
 * 6-may-02 consistently worse, but the spectrum may just be more complicated
 * T vs EM compared with BCS/GOES results from Feldman; comparison with
  OSPEX is OK 
Discussion of calibration errors and behavior of the Fe feature in these
  residuals (Dennis, Christe, Caspi, Grigis, Fletcher, Hudson) 
Discussion of Brian's lump and how to deal with it (all)
 * energies consistent with Christe's, non-thermal power above 10 keV
 * distribution functions handled by binning and also via Parnell-Jupp
  objective method => indices ~ 1.0
Discussion (Grigis) sampling method - events per hour? This was like a
  random sample, rather than a fixed period done contiguously

Kundu: RHESSI and radio
 * primarily a Nobeyama/Nancay imaging analysis based on Grigis list,
  near C1 in GOES class (disjoint sets)
 * AR 9934, May 2002 
 * May 2 example from Krucker et al
Discussion of colocation (better than 5 arc s absolute) (Dennis, White)
 * May 4 example of time-displaced 17 GHz and RHESSI spikes
Discussion
 * RHESSI spectra 
 * Nancay images, typically type III bursts 
 * conclusions: microwaves come from footpoints, meter waves often from
  IIIs. EM ~ 6e46
Discussion (Vlahos) of coregistration - consistent with common origin (White)
Discussion of strength of III association (Christe, Hudson, Benz, Kundu)
Conjecture: all flares have open field lines - rejected by consensus

Benz: micro-events in the solar corona (active + quiet)
 * older work now reported for the first time, comparing active & quiet
 * preponderance of RHESSI microflares in active regions
 * A and B level quiescent emission time compared; power-law hinted at
  for the A event Neupert-like
 * student finding softer non-thermal spectra for smaller events
Discussion (Hudson, Dennis)
 * correlations among channels => drift rate (keV/s)
 * "there are no hot nanoflares" comparing EIT nanoflares with RHESSI
  microflares 
Discussion of selection effects (Hudson, Fletcher)
 * one-hour integrations => active regions
Discussion (Kundu)
 * movie showing AR brightening

Grigis: "Where shall we go next for microflares?"
 * Are there softer HX spectra in microflare?  (Christe, Fletcher, Somov, 
  Grigis, Hudson, Dennis, Hannah, Hudson, Fletcher, Benz, Hudson, Dennis,
  Fletcher, Christe, Dennis, Christe, Veronig, Dennis)