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					    RHESSI and Radio Imaging
    Observations of Microflares
M.R. Kundu,
Dept. of Astronomy, University of Maryland, College Park, MD
G. Trottet,
Observatoire de Paris/Meudon, France
V.I. Garaimov,
Dept. of Astronomy, University of Maryland, College Park, MD
P.C. Grigis,
Institute of Astronomy, ETH Zurich, CH-8092 Zurich, Switzerland
E.J.Schmahl,
Dept. of Astronomy, University of Maryland, College Park, MD and
Lab for Astronomy and Solar Physics, NASA/GSFC
ABSTRACT

We present the analysis of five microflares

   Three observed simultaneously by RHESSI in hard X-rays and
   Nobeyama RadioHeliograph (NoRH) in microwaves (17 GHz) and
   Two observed by RHESSI and Nancay RadioHeliograph (NRH) at
   metric wavelengths (150-450 MHz).
   Since we have no radio imaging telescopes simultaneously
   operating at microwave and meter wavelengths in the same time
   zone, we use a different set of microevents for comparison with
   metric wavelength counterparts in contrast to that used for
   comparison with microwave events. This is because we are
   interested in using the locations and other imaging characteristics of
   the events from both RHESSI and Nancay instead of just temporal
   correlation.
   Here we describe the properties of five events -- three in
   microwaves and two at metric wavelengths.
  THE 2002 MAY EVENTS OBSERVED AT NOBEYAMA
 Three microwave events corresponding to RHESSI microflares occurred
in active region 9934 :

 2002 May 3 03:58 ;
 2002 May 4 05:08 ;
 2002 May 2 01:52 UT

 AR 9934 was a complex region which contained a sunspot with a
strong negative polarity of the magnetic field on the north side and a
bipolar region on the south side.

  MDI images show fast evolution of the south part of the region.
 TRACE images show many small loops in the south and the
complex loop connecting the north sunspot to the south side of
the region.

  NoRH 17-GHz maps show loop-like structure with a maximum above the
sunspot and it connects to the south side of the AR. RHESSI maps
superimposed on the NoRH maps show that X-ray emission in the range
3-25 keV are located inside the radio contours.
  During all three events HXR emission was located in the south part of the
AR. RHESSI maps for 2002 May 3 (event 1) clearly show an X-ray loop at
3-6 keV and two footpoints of the loop in the 6-12 and 12-25 keV
ranges. These footpoints are located above opposite magnetic
polarities as seen in overlays of hard X-ray images on the MDI image.

  For 2002 May 4 (event 2) HXR images show a small X-ray loop,
located close to the same position as previous event.
Footpoints of the X-ray loop are not resolved.

  Overlays of HXR images on the MDI image shows that the X-ray loop was
located above the magnetic neutral line and it connected two regions
with opposite magnetic polarities.

 During both events HXR emission was observed below 25 keV.

 Total radio flux from the X-ray emitting active region was less than 0.5 sfu.

 No significant polarization of the radio emission was observed in either case.
 2002 May 2 (event 3) is one of several microflares observed on this day,
which originated in the NE part of the active region. At 01:52:10 UT
RHESSI images in 3 energy bands 3-6 keV, 6-12 keV and 12-25 keV
overlie a 17-GHz NE source which occupies mostly an MDI negative
polarity, implying that the HXR source may be situated above the strongest
microwave source -- probably one footpoint of the microwave flaring loop.

 The NE source and another SW source seem to contribute to the
microflare emission at the same time as judged from the time profiles.

  For the maximum phase of 2002 May 3 (event 1) the HXR spectrum was
calculated. It could be fitted by three components: thermal bremsstrahlung,
atomic emission lines, and power law spectrum. Temperature of the
thermal component was about 1.6 keV; the emission measure was about 6
1046 cm-3. Slope of the power law is -3.2.
TRACE images of the AR 9934 with
MDI contours
     2002 May 03      2002 May 04
Evolution of the magnetic field
 The southern part of the active region shows fast evolution of the magnetic
 field.
May 02, 2002
 The microflare concerned occurs at 01:52 UT (first row). The RHESSI and
 NoRH images show co-located sources superposed on a MDI magnetogram.
 May 03, 2002
Left: time profiles at 17 GHz and for GOES and RHESSI (3-25 keV)
Right: contour maps at 17 GHz and HXR superimposed on MDI magnetogram
                                        The microflare concerned (03:58) is shown
                                        in the bottom row. HXR loop at 3-6 keV;
                                             T
                                        two footpoints in 6-25 keV.
                                             h
                                             e
 May 04, 2002
Left: time profiles at 17 GHz and for GOES and RHESSI (3-25 keV)
Right: contour maps at 17 GHz and HXR superimposed on MDI magnetogram


                                                            The event
                                                            concerned
                                                            starts at 0:508
                                                            UT (first row).
                                                            Note a small X-
                                                            ray loop close
                                                            to the May 3
                                                            location.
                                                            The HXR
                                                            source is
                                                            compact with
                                                            unresolved
                                                            footpoints.
X-ray spectrum fitted by three components: thermal
bremsstrahlung, atomic lines, and power law



                                            Temperature of the
                                            thermal component is
                                            about 1.6 keV;
                                            emission measure is
                                            about 6 1046 cm-3.
                                            Slope of the power
                                            law is -3.2.
Conclusions
 We have detected microwave (17 GHz) counterparts of RHESSI microflares
 observed in the energy range 3-50 keV.
 The microwave emission comes from the foot points (for higher energies),
 and from the entire small (mini) flaring loop (for lower energies).
 The relative positions of microwaves and hard X-rays in the higher energy
 channels are as they should be in normal flares. Sometimes the two
 (microwave & hard X-ray) sources coincide, at other times the two are at
 opposite ends of the mini flaring loop. One sees the mini flaring loops
 clearly in NoRH images.
 The hard X-ray spectrum of microwave associated RHESSI micro flares can
 be fit by a thermal component (EM~6*1046 cm-3 at 3-6 keV) at low energies
 and (sometimes) a nonthermal component (with slope -3.2) at higher
 energies.
 At metric wavelengths the type III bursts are often spatially associated
 with RHESSI microflares. This must have important implications in the
 propagation of energetic electrons up thru the corona.
 This result combined with microwave results should provide a good
 understanding of the topology of coronal structures in which energetic
 HXR emitting electrons propagate.
Nancay events
 Unfortunately we have no radio imaging telescopes simultaneously
 operating at Microwave and meter wavelengths in the same time
 zone.
 So we’ve used the Nancay(France) metric radioheliograph at 150-
 450 MHz to study metric counterparts of RHESSI micro-flares and
 used a different set of microflares for comparison with metric
 events as opposed to that used for comparison with microwave
 events.
 This is because we want to use the locations of events from both
 RHESSI and Nancay and not just temporal correlation. Here we
 present a preliminary analysis of such a study.
 Since both RHESSI HXR and metric type IIIs are produced by
 beams of electrons, type IIIs are the obvious candidates for such a
 comparison. We confirmed our identification of bursts by using
 Potsdam spectral data.
Aug. 05, 2003




                Top Left: RHESSI time profile of a microflare,
                along with Nancay burst time profiles at
                150,164,236 MHz. Bottom Left: EIT image with
                RHESSI and Type III positional data at three
                frequencies. The RHESSI source is very
                compact.
                Middle top panel: MDI image with RHESSI
                microflare position.
                Right top: Potsdam type III bursts
Sep. 03, 2003




                Top Left: RHESSI time profile of a micro
                flare, along with Nancay burst time profiles
                at 150,164,236,327,410 MHz. Bottom Left:
                EIT image with RHESSI and Type III
                positional data at five frequencies. Note the
                very compact RHESSI source.
                Right top: Potsdam type III bursts
Concluding Remarks

 Our main conclusion is that RHESSI micro
 flares are often spatially associated with
 metric type III bursts. This must have
 important implications in the propagation of
 energetic electrons up thru the corona.
 This result combined with microwave results
 should provide a good understanding of the
 topology of coronal structures in which
 energetic HXR emitting electrons propagate.

				
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