RHESSI and Radio Imaging Observations of Microflares

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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, Observatoir
e 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
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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.

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THE 2002 MAY EVENTS OBSERVED AT NOBEYAMA

• Three microwave events corresponding to RHESSI
  microflares occurred
• in active region 9934
• 2002 May 3 0358
• 2002 May 4 0508
• 2002 May 2 0152 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

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• 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.

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• 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 015210 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.

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TRACE images of the AR 9934 with MDI contours
2002 May 03
2002 May 04
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Evolution of the magnetic field
The southern part of the active region shows fast
evolution of the magnetic field.
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May 02, 2002
The microflare concerned occurs at 0152 UT
(first row). The RHESSI and NoRH images show
co-located sources superposed on a MDI
magnetogram.
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MDI images with 17GHz and RHESSI contours of AR
9934
2002 May 03
May 04, 2002
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Time profiles of 17GHz and X-Ray time profile and
spectrogram
2002 May 03
The dashed vertical line indicates the start of
the microevent.
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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 (0358) is shown in the
bottom row. HXR loop at 3-6 keV two footpoints
in 6-25 keV.
The
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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 0508 UT (first
row). Note a small X-ray loop close to the May 3
location. The HXR source is compact with
unresolved footpoints.
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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.
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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 (EM61046 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.

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Nancay events

• Unfortunately we have no radio imaging telescopes
  simultaneously operating at Microwave and meter
  wavelengths in the same time zone.
• So weve 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.

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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
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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
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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.