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