Radio Diagnostics of Energetic Electrons from Solar Flares, CMEs and

Shocks:

Nicole VilmerLESIA Observatoire de Paris

UMR 8109 CNRS, UPMC, Université Paris-Diderot

ESPM 14 8-12 SEPTEMBER 2014TRINITY COLLEGE DUBLIN

DUBLIN

Electromagnetic radiation from energetic electrons

Dauphin et al., 2005

X-rays

MicrowavesGyrosynchrotron Emissions

Meter wavesPlasma emissions

Energetic electrons from the active Sun produce electromagnetic radiation in a very extended domain :

X-ray and Gamma-ray emissions

Radio emissions in the 10 kHz to >500 GHz domain

IIm

fb(Hz)= 2.8 1B (G)

fp(kHz)=9ne

cm- 3

INPUT of RADIO OBSERVATIONS in the GHz-MHz range

to SOLAR and HELIOSPHERIC PHYSICS

- What are the physical mechanisms leading to particle acceleration?

- What are the physical mechanisms leading to instabilities and eruptive activity in the coronal plasma?

1 GHz

100 MHz

10 MHz

1 MHz

INPUT of RADIO OBSERVATIONS in the 1 GHz-1 MHz range to SOLAR and HELIOSPHERIC PHYSICS

Plasma radio emissions from « non-thermal » electrons predominant below 1 GHz

Particle acceleration in flares and CMEs

Propagation of particles from the acceleration site to the interplanetary medium

Triggering and evolution of coronal mass ejections and shocks in the low corona

Radio emissions are TRACERS of dynamical processes (e.g. shocks) and of electron propagation in the corona and interplanetary medium.

Type III ( e beams)

Type II (shock)

Wind/WAVES(satellite)

Nançay DAM

Nançay ORFEES

Spectral identification of imaged radio sources

Nançay NRH

150 MHzPositions (2X1D) of radio

sources

http://radio-monitoring.obspm.fr/index.php

fp = 9 √ Ne

(kHz) cm-3

Radio emissions in the corona

2 Rs

NRH

LOFAR

VLA, OVSA

CSRH

327 MHz237 MHz164 MHz

Radio diagnostics of electron beams acceleration sites? propagation in the corona, in the interplanetary medium? Injection from the flare site to the IP medium? Radio diagnostics of shocks and

CMEs acceleration sites? origin of the shock wave?

~10000 types III « bursts » observed by the NRHin the frequency range 450-150 MHz from 1998 to 2008 (Saint-Hilaire, et al. , 2013)

Statistical studies on « coronal » type III bursts: flux distributions

Number of type III events in 3 months (with NRH observations)Blue: f 10.7 index (SFU)Red: Sunspot number

Statistical studies on « coronal » type III bursts:

Very close to results for radio bursts at higher frequencies (above 1GHz) slope of (-1.8)(Nita et al., 2002)Variation of radio flux with

frequency

(See also results on a type III burst between 3-50 MHz (Dulk et al., 2001)Constraints to type III emission models?

dN/dS= 0.34 ν−2:9S−1.7sfu-1 day-1

(( sfu−1 day−1

Coronal and Interplanetary type III bursts?

What about interplanetary type III bursts??

156 interplanetary Type III bursts with Stereo

Peak at 1 MHz for 156 type III bursts observed with STEREO (see Krupar et al., 2014)

Electron acceleration sites?

ARE THE TYPE III GENERATING ELECTRONS A PART OF THE SAME POPULATION AS HXR GENERATING ELECTRONS?

A question debated for many years:(e.g. Kane, 1971; 1981; Raoult et al., 1985, Hamilton, et al., 1995; Aschwanden et al., 1995; Benz et al., 2005; 2007)

Some Recent Results!

Radio and X-ray diagnostics of flare energetic electrons

Vilmer et al. 2002

RADIO

X-RAYS

One of the cartoon (how common?)

Electrons travelling downwards into the chromosphere radiate X-rays in dense (ne=1012 cm-3) plasma via Bremsstrahlung. Detected X-rays are usually in the 6-100 keV energy rangeElectrons travelling upwards can induce Langmuir waves which in turn produce coherent radio emission (type III) in the rarefied (ne<109 cm-3) coronal and interplanetary plasma. Detected radio frequencies are from around 400 MHz down to 2 MHZ

Standard picture ?Electron acceleration in the coronaPropagation both upwards and downwards. NRH and RHESSI

observations

ARE THE TYPE III GENERATING ELECTRONS A PART OF THE SAME POPULATION AS HXR GENERATING ELECTRONS?

For some events : YES See correlations between type III starting frequencies and HXR spectral index

Starting frequency of the radio type III burst (red) and HXR spectral index (green)

Reid, et al. 2011See also Raoult et al., 1985

ARE THE TYPE III GENERATINGELECTRONS A PART OF THE SAME POPULATION AS HXR GENERATING ELECTRONS?For some events : YES Is it the common rule?

Systematic search using RHESSI flare list and PHOENIX 2 catalogue of type III bursts30 events between 2002 and 2009

17/30 events (50% ) with correlations Use of a density model (exponential model derived from Saint Hilaire et al., 2013) to change frequency to height and thick target model to go from HXR spectral index to electron spectral index. Conclusion: For half of the events type III generating electrons are part of the same population as HXR generating electrons-

CC=-0.86

Reid et al., 2014

CC=0.85

Deducing the characteristics of acceleration region: height and size d using combined radio and X-ray observations and numerical simulations (Reid et al., 2011, 2014)

10 events: h (acceleration height) in the 25Mm to 180 Mm ranged (acceleration size) in the 2.1 to 16 MmConclusion: Extended acceleration region «high » in the coronaBUT flares with open field lines (metric type III burts) 

What are the characteristics of the acceleration region?

onacceleratitypeIII hdh

From X-rays time of flight measurements H~ 20 Mm (see Aschwanden et al. , 1998))

Need of future imaging spectroscopy < 500 MHz(e.g. Chinese Solar RadioHeliograph,FASR,…)

Tracing electron beams in the corona with radio dynamics imaging

spectroscopyFirst observations of type IIIdm bursts1-2 GHzWith the new technique ofradio dynamic imaging spectroscopy recently upgraded Karl G. Jansky Very LargeArray (VLA). (Chen et al., 2013)Energy release height < 15 MmNote the spread of Positions at a given finjection of electron beamsin a fibrous coronaD<100 km

More to be learnt with the CSRH…

Tracing the path of electron beams in the corona to the IP medium

NRH

fluxRH

ESSI fluxRadio spectrum

Do all coronal type III bursts have X-ray counterparts?30% to 50% of type III events (only type III emissions) havea ssociated hard X-ray flares. Do all coronal type III bursts have an interplanetary counterpart?50% of events have emission < 14 MHz Bias for the more intense events having interplanetary emissionStudy based on >1000 type III bursts over 10 years of data

See poster by Reid,Vilmer

Flare Morphology

The “ standard” flare model is

very simplified. The reality is

more complicated

Particles can be injected into

different magnetic

structures during the course of a

flare.

This can influence whether the

electron beam makes it into

interplanetary space.

Tracing radio emitting electron beams in the corona to

the IP mediumLOFAR observations of type III radio burts at 50-55 MHz, 40-45 MHz and 30-35 MHz(tied-array mode) see Morosan et al., 2014 and talk

Type III sources at theflank of the CME

Another site of electron acceleration …Also seen at lower frequencies…

Radio diagnostics of electron beams acceleration sites? propagation in the corona, in the interplanetary medium? Injection from the flare site to the IP medium? Radio diagnostics of energetic

electrons from CMEs and shocks acceleration sites? origin of the shock wave?

Where are the electron acceleration sites

in the corona?Role of the Coronal Mass Ejection CME development and propagationCME interaction with other magnetic structures (open B lines, streamers) for the production of energetic electrons

Related to the shock wave?? (1)In the reconnection sheet formed below the CME?? (2)In the interaction regions during the evolution of the magnetic features ?? (3)

INPUT OF RADIO IMAGES…

Adapted from Démoulin et al., 2012

11

2

3

Electron acceleration in current Sheets in flares and CMEs

Evidence from Spectrography

Multifrequency imaging

Reconnection

Pick, Démoulin et al., 2005

Kliem, et al. 2000,Karlicky et al., 2002, 2004

S

M

Quasi periodic episodes from magnetic

reconnection in CS

Evidence for electron acceleration due to CME interaction

Electron acceleration (type III bursts) due to reconnection at the lateral flanks of CMEs

Démoulin et al., 2012

Type III position at 164 MHz and movement

Radio CME

Electron acceleration (herringbones) due to shock acceleration at the lateral flank of the CME Carley et al.,

2013

Positions of the bursty source at 150 MHz

- Shock in flares and CMEsCoronal type II bursts: signature of MHD shock waves (Wild & Smerd, 1972; Mann, 1995; Cairns 2011,…)Origin of the coronal shock wave?Flare blast wavePiston driven shock (eruptive magnetoplasma) structure A lot of discussions(Aurass 1997; Cliver et al., 1999; Vrsnak & Cliver 2008,…)Need to study the relative positions of radio type II sources and eruptive plasmaBut very few observations of type II bursts starting at high enough frequencies to compare positions of radio type II sources (e.g. with the NRH) with the positions of eruptive plasmas (seen in X-ray, EUV) A few studied cases of type II bursts starting at HF (~ 500 MHz)Gopalswamy et al., 1997; Klein et al., 1999; Dauphin et al., 2006, Magdalenic et al., 2010, Magdalenic et al., 2012; Bain et al., 2012; Zimovets et al;, 2012; Zucca et al., 2014 & posters

Klein et al., 1999

3

Positions of radio sources at the beginning of the type II emission at each frequencySource at 432 MHz above the LE of hot plasmaIncrease of the distance between the LE and the type II positions at lower frequencies

Origin of the shock in the low corona

Zimovets et al., 2012

Hot

Hot plasmacentroid /leading edge500 km/s

Type II1500- 2000km/s

Warm plasma 1100 km/s

Origin of the shock in the low coronaFlare blast wave or

piston driven? Two strong evidences in favour of the piston-driven shock wave scenario for this case: -location of the type-II burst source above the apex of the eruptive plasma leading edge -similar propagation direction of the type II and LE of the eruptive plasma But: how to explain the difference between the velocity of Leading edge of the eruptive plasma and the velocity of the shock (type II sources)?See e.g. numerical simulations of the propagation of a shock wave in a gravitationally stratified corona the shock wave (once created) can propagate faster through the corona than its driver .(piston driven and then freely propagating blast wave) See also very recent Type II/CME/ejecta observations by Carley, Pick (posters)

Pomoell et al., 2008

FR

shock

Origin of the shock in the interplanetary mediumGeneral agreement on the origin of Interplanetary

Shocks (IP shocks): CME driven (Cane et al. 1987; Gopalswamy et al., 2000)

Where are the radio type II sources in the IP Medium??

- Positions derived through triangulation of emissions observed by 2 spacecrafts ( STEREO B and WIND ) from 625 to 425 kHz

- 3D reconstruction of the CME (SOHO, STEREO)

Magdalenic et al., 2014

The source of the type II burst is at the southern flank of the CME!Close to the location of the interaction of the CME/shock and nearby coronal streamer!!

Observations of type II sources with LOFAR??

Magdalenic et al., 2014

See also talk by Susino

Radio Diagnostics of Energetic Electrons from Solar Flares, CMEs and Shocks

Radio emissions (1GHz-100 kHz) are TRACERS of dynamical processes (e.g. shocks) and of electron propagation in the corona and interplanetary medium

Electron acceleration sites?

Acceleration regions deduced from x-rays, radio imaging at 1 GHz<15 Mm,Combined X-ray/ radio observations (25 -200 Mm)BUT NO Images yet of the acceleration sites Input of radio images and spectra below 500 MHz! CSRH, FASR, other decimetric radioheliographs?)

Role of the CME development and interaction with ambient magnetic structureDifferent sites for electron acceleration (in extended CS below the CME flux rope, in interaction regions with surrounding B fields?

Formation of the shock ?Input of radio images below 100 MHz (LOFAR observations) Combination with space missions