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)

YOHKOH/HXT coronal above the loop top > 30 keV X-ray sources in impulsive flares (Masuda, 1994; Masuda et al., 1998) (< 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 h> 5104km

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

From Masuda et al 1998

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 configurationLoop-loop reconnection

Interpretation in the scheme of magnetic reconnection above (outside the bright soft X-ray loop) the loop top:

cartoon from Masuda et al, 1998

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

GOES M2.5 AR 9893AR 9893 N21 W81 large part behind the limbH 1310-1320-1332 N23 W88 SF AR 9893 < 1323- 1338 N19 W67 SF AR9901

Coronal HXR source from 13:07 UT

H 8 days earlier

RHESSI images 12-25 keV10’’ above the limbafter 1307 UT

movie_trace+hessi1225.htmlmovie_trace+hessi2550.html

Comparison of RHESSI images with TRACE images at 195 Å =flare plasma at 15 MK

TRACE and RHESSI 12-25 keV images before 13:07 UT (no coronal HXR sources)movie_trace+hessi1225_125500.html

TRACE and RHESSI 12-25 keV and 25-50 keV images after 13:07 UT(coronal HXR of the event sources with most of the time no footpoints Most energetic part )

RHESSI 25-50 keV images

Associated radio emissions??

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)

RHESSI

6-12 keV

12-25 keV

25-50 keV

19.6 GHz

11.8 GHz

8.4 GHz

Coherent radio emissions in dm/m wavelengths

Spectrum ETH ZürichRadio type III burstse beams in the coronalimited range(< 350 MHz)limited time range (30 s)

Flux at 3 in the flare regionfrom the Nançay Radioheliograph+Images at 327 MHz

NRH 327 MHz

NRH 236 MHz

NRH 164 MHz

3-6 keV

6-12 keV

25-50 keV

12-25 keV

327 MHz

Limited duration ofAssociated dm emissions

Consistent with the observations that10 to 15 % of HXR producing electrons have no detectable emission at decimeter and longer wavelengths

(e.g. Simnett and Benz, 1986). t

NRH 327 MHzduring 4 burstsBetween 131120 and 131140

RHESSI25-50 keV

NRH 327 MHz

during 4 bursts

Between 131120 and 131140

RHESSI25-50 keV

Summary/discussion• In the most energetic part of the HXR event, coronal HXR sources with

no (permanent) footpoints

• Coronal HXR sources (> 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.

Simple 2D sketch

More complex at 3D

with several loop systems as suggested by TRACE

e-beams

X-rays

cm and HXR emission: gyrosynchrotron emission from electrons in low-lying B loops

Most of the event: no dm/m emissionsNo 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 electronsRadio 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.