NoRH Observations of RHESSI Microflares

1
NoRH Observations of RHESSI Microflares

• M.R. Kundu,
• Dept. of Astronomy, University of Maryland,
  College Park, MD
• E.J.Schmahl,
• Dept. of Astronomy, University of Maryland,
  College Park, MD and Lab for Astronomy and Solar
  Physics, NASA/GSFC
• V.I. Garaimov,
• Dept. of Astronomy, University of Maryland,
  College Park, MD
• P.C. Grigis,
• Institute of Astronomy, ETH Zurich, CH-8092
  Zurich, Switzerland

2
ABSTRACT

• We present a summary of the analysis of more than
  two dozen microflares, observed simultaneously by
  RHESSI in hard X-rays and Nobeyama
  RadioHeliograph (NoRH) in microwaves (17 GHz).
  The RHESSI microflares are observed in the energy
  range 3-25 keV. The observations were made 2002,
  May 2-6.
• We describe the imaging characteristics of these
  microflares including
• their locations in hard X-rays and
  microwaves and the relative positions of the
• micro-flaring sources relative to MDI
  magnetograms.
• We discuss the brightness temperatures, emission
  measures and their hard X-ray spectral
• properties. One sees the mini flaring loops
  clearly in NoRH images. The microwave
• emission often seems to come from the
  RHESSI foot points (for higher energies), and
  from the entire small (mini) flaring loop (for
  lower energies).
• Sometimes the two (microwave HXR) sources
  coincide, at other times they are at opposite
  ends of the mini flaring loop.
• Typically, the hard X-ray spectrum of the
  microwave associated RHESSI microflares can be
  fit by a thermal component at low energies(3-6
  keV) and a nonthermal component at higher
  energies (12-25 keV).

3
THE 2002 MAY EVENTS OBSERVED AT NOBEYAMA

• More than two dozen microwave events
  corresponding to RHESSI microflares
• were observed in our May 2002 observing period.
  Several active regions including
• AR 9934 were involved. We shall discuss only
  some events observed 2002 May2-6.
• 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 a maximum above the
  sunspot and there is
• also emission on 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.

4

• 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.

5

• The 2002 May 2 0152 event 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 the 2002 May 3,0358
  microflare, 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.

6

May 02
May 03

7

May 03
May 04
8

• May 05

May 06
9
2002 May 02

• 17 GHz time profile

• RHESSI 3-25 keV

• RHESSI spectrogram

10
May 02

• Grayscale 17 GHz, contours RHESSI bands 3-6,
  6-12 12-25 keV (top to bottom)
• Bottom row shows background-subtracted 17 GHz
  maps
• In all these events, the HXR source appears
  close to, but somewhat displaced limbward of the
  17 GHz source

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May 02

12
May 02

• The RHESSI and NoRH images at 4 different times
• The maps are superposed on a MDI magnetogram.

13
2002 May 03

• 17 GHz time profile

• GOES 1-8 A profile

• RHESSI 3-25 keV

• RHESSI spectogram

14
May 03

• Faint 17-GHz
• feature in all 3 cases

• In HXR these micro-
• flares are single, and
• each is displaced from
• the 17 GHz sources.
• Each HXR micro-
• flare has significant
• emission in the 12-25 keV
• band.

15
May 03

• The 0355 microflare difference
• map (bottom row) shows a loop-like
• microwave feature connecting the
• HXR source to the bright, compact
• 17 GHz component 100 to the
• north.
• The 0358 microflare in all HXR
• bands shows a loop and footpoints.
• This RHESSI loop is probably the
• same as the 0355 microwave loop.
• In the 0415 event, the HXR
• source is single elongated,
• suggestive of a loop displaced
• eastward of the earlier loop.

16
May 03

• The microflare at 0401
• very compact, unresolved,
• and is exactly co-spatial in
• HXR and 17 GHz.
• The other two HXR micro-
• flares are slightly offset
• but nearly coincident with
• the brightest 17 GHz source.
• It is possible that the 17
• GHz is at one end/footpoint
• of the RHESSI loop-like
• structure.

17
2002 May 03
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 at 0358 is shown in the bottom
row. HXR loop at 3-6 keV two footpoints in 6-25
keV.
The
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2002 May 3 0358 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.
19
2002 May 04

• 17 GHz time profile

• GOES 1-8 A profile

• RHESSI 3-25 keV

• RHESSI spectogram

20
2002 May 04

• The HXR source lies
• close to a weak 17 GHz
• source
• The HXR source is visible in
• all three bands in two events

21
May 04

• The background-
• subtracted maps at 0543
• and 0545 show that
• RHESSI sources in the two
• lower bands are close to
• a 17 GHz source

• The FOV of the 17-GHz map does not overlap the
  RHESSI microflare at 0554 UT.

22
2002 May 04
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.
23
2002 May 05

• 17 GHz time profile

• GOES 1-8 A profile

• RHESSI 3-25 keV

• RHESSI spectogram

24
May 05

• Time profiles of different
• components of 17 GHz
• microflare-producing
• region.

• Note that microflares at
• different times can come
• from different components
• of active regions.

25
2002 May 05

• MDI images along with 17 GHz and RHESSI contours
• Note the RHESSI loop-like structure and single
  sources at the
• boundary between positive negative polarities,
  suggestive of mini-loops

26
2002 May 06

• 17 GHz time profile

• RHESSI 3-25 keV

• RHESSI spectogram

27
May 06

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TRACE images of the AR 9934 with MDI contours
2002 May 03
2002 May 04
29
MDI images with 17 GHz and RHESSI contours of AR
9934
2002 May 03
2002 May 04
30
RHESSI SPECTRA 2002 May 02 Model fits of
thermal, line, power law components
014630
015130
015000
015340
31
RHESSI SPECTRA 2002 May 03
035730
040030
040000
040300
32
2002 May 03
050600
Model fits of thermal, line, power law
components
050900
33

RHESSI HXR spectra for the May 3, 0358 event.
Each panel shows a 5-component fit for a 12-s
time bin using thermal, atomic line emission and
nonthermal bremsstrahlung.
The components are Temperature (T), emission
measure (E), spectral index (g), 20-keV flux
(F20), and lower cutoff (Eturn)
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Conclusions

• Microwave (17GHz) micro-events are always
  associated with RHESSI microflares observed in
  the energy range 3-25 keV. This is certainly true
  for all stronger microflares considered here.
• RHESSI microflares have loop-like structures in
  lower energy bands (3-6,6-12 keV) and foot point
  emission usually in higher energy band (12-25
  keV).
• The microwave emission comes from the foot
  points, and from the entire small (mini) flaring
  loop (for lower energy HXR events).
• The relative positions of microwaves and hard
  X-rays in all energy bands are similar to what is
  observed 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. Sometimes one sees the mini
  flaring loops clearly in NoRH images.

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Conclusions (continued)

• Time profiles of different components of the
  17GHz AR show that successive events may come
  from different component sources.
• The hard X-ray spectrum of a typical
  microwave-associated RHESSI micro flare 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.
• Sometimes one observes compact, unresolved
  co-located HXR microwave micro-events.
• To be continued at nbym_06