Coronal hard X-ray sources and associated decimetric/metric radio emissions

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Coronal hard X-ray sources and associated
decimetric/metric radio emissions

• N. Vilmer
• D. Koutroumpa
• (Observatoire de Paris- LESIA)
• S.R Kane
• G. Hurford
• (Space Sciences Laboratory Berkeley)

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• HXR in solar flares ? acceleration and
  propagation of energetic electrons
• interacting at the Sun
• Bulk of HXR emission from footpoints of flaring B
  loops by electrons accelerated
• in the low corona (109-1010 cm-3) near the loop
  top

• YOHKOH/HXT ?coronal above the loop top gt 30 keV
  X-ray
• sources in impulsive flares (Masuda, 1994
  Masuda et al., 1998)
• (lt 6 events)
• Compact above the loop top source together with
  double footpoint sources
• 10 above the SXR loop apex
• Relatively hard spectrum
• Located at slightly higher altitudes at higher
  X-ray energies.
• 1 event (Sato, 2001) without footpoints
• Extended source above 30 keV at hgt 5104km

From Masuda et al 1998
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Interpretation in the scheme of magnetic
reconnection above (outside the bright soft
X-ray loop) the loop top

• energization of electrons in the
• reconnection site itself or
• at the place where the downward hot plasma from
  the reconnection site collides with underlying
  closed B loops
• Different types of interpretation for
  reconnection sites
• Loop with a cusp configuration (Masuda)
• Emerging flux type configuration
• Loop-loop reconnection

cartoon from Masuda et al, 1998

• Here observations of coronal above the loop top
  HXR sources with
• RHESSI and time evolution in the flare

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GOES M2.5 AR 9893 AR 9893 N21 W81 large part
behind the limb H? 1310-1320-1332 N23 W88 SF AR
9893 lt 1323- 1338 N19 W67 SF AR9901
H?? 8 days earlier
Coronal HXR source from 1307 UT
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• RHESSI images 12-25 keV
• 10 above the limb
• after 1307 UT

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movie_tracehessi1225.htmlmovie_tracehessi2550.h
tml
Comparison of RHESSI images with TRACE images
at 195 Å flare plasma at 15 MK

• TRACE and RHESSI 12-25 keV images before 1307 UT
• (no coronal HXR sources)
• movie_tracehessi1225_125500.html

• TRACE and RHESSI 12-25 keV and 25-50 keV images
• after 1307 UT
• (coronal HXR of the event sources with most of
  the time no footpoints Most energetic part )

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RHESSI 25-50 keV images
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(No Transcript)
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Associated radio emissions??
6-12 keV
RHESSI
12-25 keV

• Gyrosynchrotron emission from energetic flare
  associated
• electrons in the cm/mm domain
• Observations at 3 ? from Bern
• Similarity between durations of 30 keV HXR and
  cm emissions
• from energetic electrons
• (as usually observed)

25-50 keV
19.6 GHz
11.8 GHz
8.4 GHz
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Coherent radio emissions in dm/m wavelengths
Spectrum ETH Zürich Radio type III bursts e beams
in the corona limited ? range (lt 350 MHz) limited
time range (30 s)

NRH 327 MHz
Flux at 3 ?? in the flare region from the Nançay
Radioheliograph Images at 327 MHz
NRH 236 MHz
NRH 164 MHz
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3-6 keV
6-12 keV
12-25 keV
Limited duration of Associated dm emissions
Consistent with the observations that 10 to 15
of HXR producing electrons have no detectable
emission at decimeter and longer wavelengths
(e.g. Simnett and Benz, 1986). t
25-50 keV
327 MHz
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NRH 327 MHz during 4 bursts Between 131120 and
131140
RHESSI 25-50 keV
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• NRH 327 MHz
• during 4 bursts
• Between 131120 and 131140

RHESSI 25-50 keV
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Summary/discussion

• In the most energetic part of the HXR event,
  coronal HXR sources with no (permanent)
  footpoints
• Coronal HXR sources (gt 10 ) above the limb,
  displaced (above) the hot magnetic structures
  seen with TRACE
• 25-50 keV coronal sources above 12-25 keV sources
• Consistent with the previous ( 6 ) observations
  with YOHKOH/HXT
• More dynamic behaviour from TRACE observations,
  suggestion of loop-loop interactions between 2
  loop systems with one system apparently connected
  to parts of the AR behind the limb . Appearance
  of the coronal sources and of the most energetic
  part of the event at the time of the interaction.
• No footpoints most of the loop structures
  connected to parts behind the limb. Only the
  emission from the region close to the
  reconnection sites(s) but rather loop-loop
  reconnections.

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• cm and HXR emission gyrosynchrotron emission
  from electrons in low-lying B loops
• Most of the event no dm/m emissions
• No electron access to high or open B field lines
  seen from the earth
• Energetic electrons are only present in small
  scale loops as seen from the earth
• After abrupt reformation of low lying B field
  lines through sequence of loop-loop interactions,
  the B field reconfiguration may extend over
  larger distances and reach overlying open field
  lines seen from the earth
• possible acceleration sites for radio emitting
  electrons
• Radio dm/m emissions at the time of appearance of
  second component of 25-50 keV source indicating
  displacement of energy release site and possible
  electron access to new B lines.

e-beams
X-rays
Simple 2D sketch More complex at 3D with several
loop systems as suggested by TRACE