Title: NoRH Observations of RHESSI Microflares
1NoRH 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
2ABSTRACT
- 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).
3THE 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 06
92002 May 02
10May 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
11May 02
12May 02
- The RHESSI and NoRH images at 4 different times
- The maps are superposed on a MDI magnetogram.
132002 May 03
14May 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.
15May 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.
16May 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.
172002 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
182002 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.
192002 May 04
202002 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
21May 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.
222002 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.
232002 May 05
24May 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.
252002 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
262002 May 06
27May 06
28TRACE images of the AR 9934 with MDI contours
2002 May 03
2002 May 04
29MDI images with 17 GHz and RHESSI contours of AR
9934
2002 May 03
2002 May 04
30RHESSI SPECTRA 2002 May 02 Model fits of
thermal, line, power law components
014630
015130
015000
015340
31RHESSI SPECTRA 2002 May 03
035730
040030
040000
040300
322002 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)
34Conclusions
- 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.
35 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