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The Radio Sun NoRH 17 GHz / 1.8 cm VLA 1.4 GHz / 21 cm NRH 0.327 GHz / 91 cm Karl-Ludwig Klein Observatoire de Paris - Meudon

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Presentation on theme: "The Radio Sun NoRH 17 GHz / 1.8 cm VLA 1.4 GHz / 21 cm NRH 0.327 GHz / 91 cm Karl-Ludwig Klein Observatoire de Paris - Meudon"— Presentation transcript:

1 The Radio Sun NoRH 17 GHz / 1.8 cm VLA 1.4 GHz / 21 cm NRH GHz / 91 cm Karl-Ludwig Klein Observatoire de Paris - Meudon

2 The solar corona © C. Viladrich, SAF EUV images - SoHO/EIT Magnetograms - SoHO/MDI A >1 MK plasma whose structure and dynamics are governed by magnetic fields emerging fom the interior.

3 Emission processes 1 : thermal plasma –free-free –gyroresonance (enhanced opt depth at = s ce ; s=2, 3, 4) Radio observations of the solar atmosphere Radio waves from the solar atmosphere : –propagation at > pe  n e  decreases with increasing altitude –sounding of different heights at different frequencies (0 R S -1 AU) NoRH 17 GHz / 1.8 cm VLA 1.4 GHz / 21 cm NRH GHz / 91 cm

4 Emission processes 2 : radio bursts –(gyro)synchrotron (cm- m- ) –collective emission at pe or 2 pe ( pe  n e ; bursts, dm-m- )  identification of moving exciters : electron beams, shock waves Radio observations of the solar atmosphere Radio waves from the solar atmosphere : –propagation at > pe  n e  decreases with increasing altitude –sounding of different heights at different frequencies (0 R S -1 AU) ETH Zurich AIP Potsdam - OSRA Tremsdorf

5 Solar radio astronomy in Europe

6 Accessible from ground:  1 mm–30 m (  300 GHz-10 MHz) Solar radio instrumentation 2 types of observations :  Spectroscopy of the whole Sun (bursts)  Aperture synthesis imaging

7 Plasma diagnostics of the corona (n e, T, B) and the origin of the solar wind Large-scale coronal disturbances: mass ejections (CME), shocks The Sun as a particle accelerator : –Mildly relativistic electrons in flares (gyrosynchrotron) –« Quiet-time » non thermal e - -populations –e - accelerated during CME and at coronal shocks –Energetic particle acceleration and propagation in the corona and interplanetary space Observations of the solar corona at radio

8 Plasma diagnostics of the corona (n e, T, B) and the origin of the solar wind Large-scale coronal disturbances: mass ejections (CME), shocks The Sun as a particle accelerator : –Mildly relativistic electrons in flares (gyrosynchrotron) –« Quiet-time » non thermal e - -populations –e - accelerated during CME and at coronal shocks –Energetic particle acceleration and propagation in the corona and interplanetary space Outlook: solar radio telescopes for the future Observations of the solar corona at radio

9 Radio emission of the quiet solar atmosphere Plasma diagnostics (n e, T, B) of an extended region from the chromosphere to the corona

10 + - h A multi frequency view of the radio Sun 2004 Jun Jun Jun Jun 29 Nançay Radioheliograph 410 MHz Siberian Solar Radio Telescope 5.7GHz Nobeyama Radioheliograph 17 GHz Different structures at  : active regions (GHz), coronal holes

11 Brightness temperature [K] Wavelength [m] T b (coronal hole) Low : T b = T e = 6.7  10 5 K High : T b << T e n e = 2.3  10 8 cm -3 T b (average corona) Mercier & Chambe 2009 ApJ 700, L137 Coronal plasma parameters Bremsstrahlung: brightness spectrum depends on n e & T e Nançay Radioheliograph

12 Gyromagnetic radiation Electron cyclotron frequency Low speed electron (T=10 6 K) : cyclotron line (unobservable in corona, since pe > ce ) and low harmonics ( =s 0, 0 = ce, s=1,2,3) Synchrotron rad., relativistic e: 0 = ce /  ; beaming  high s, max. intensity at Intensity Time Frequency B

13 =s ce (s=2 … 4 for T e  2  10 6 K) -> 5 GHz (6 cm) if s=3, B=600 G Resonant surf., depth ~100 km =5 GHz, s=3 =8,4 GHz, s=3 chromosphère 600 G 1000 G >3 ce,max Gyroresonance emission: a tool for coronal magnetic field measurements Gyroresonance emission

14  gr >1 : T b on iso-B surface ( =s ce ; in general not plane) Above sunspots (intense B) Confirmed technique: cf. Alissandrakis, Kundu, Lantos 1980, A&A 82, 30 Future: broadband spectrographic imaging Lee et al. 1999, ApJ 510, 413Lee et al. 1998, ApJ 501, 853 Gyroresonance emission: a tool for coronal magnetic field measurements Optical + VLA

15 The corona emits bremsstrahlung at cm-to-m- (quiet corona), optically thin or thick. –Determination of coronal plasma parameters from bremsstrahlung spectrum (n e, T e ); comparison with othe diagnostics (EUV line spectroscopy); origin of solar wind; nature of coronal electron population (maxwellian ?) –Determination of coronal magnetic fields: circular polarisation of optically thin bremsstrahlung, depolarisation (not shown here), gyroresonance emisssion. Perspective : Multi-frequency mapping of the Sun by the Frequency Agile Solar Radiotelescope (FASR). Not addressed here: recombination lines from the chromosphere. ALMA ? Further reading : Aschwanden, Physics of the Solar Corona; papers in Solar and Space Weather Radiophysics, see FASR web site Thermal radio emission from the solar corona: summary

16 Bursts of gyrosynchrotron radiation from solar flares Evidence of electron acceleration to relativistic energies in the corona

17 Observed microwave spectra Whole Sun spectra of solar radio bursts: Nita et al 2004 ApJ 605, 528 Owens Valley Solar Array

18 Observation of a microwave burst spectrum with dense frequency coverage (Owens Valley Solar Array) Continuous spectrum (practically)  >>0,  >1 : gyrosynchrotron radiation (  1,  >>1 : synchrotron radiation) Corona: hundreds of keV, occasionally higher energies Observations : Owens Valley, Nita, Gary, Lee 2004, ApJ 605, 528 Opt. thick Opt. thin Gyrosynchrotron interpretation

19 Solar radio burst : usually observed up to some tens of GHz. New: =212 GHz (SST 1 ): synchrotron emission from relativistic e - :   =10 Slope of the microwave spectrum Trottet et al A&A Relativistic electrons at the Sun (1) Univ. Mackenzie Sao Paulo

20 Time profile (microwaves, HXR, gamma-rays): electron acceleration from 100 eV (quiet corona) to hundreds (sometimes tousands) of keV in a few seconds to a few tens of seconds Consistent with e-spectrum inferred from gamma-ray bremsstrahlung (h > 300 keV; Trottet et al AA 334, 1099 ) Relativistic electrons at the Sun

21 A gyrosynchrotron model source Bastian, Benz, Gary 1998, ARAA Optically thick: loop top Optically thin: foot points More detailed models: Preka-Papadema & Alissandrakis AA 139, 507; 1988 AA 191, 365: 1992 AA 257, 307 Klein & Trottet 1984, AA 141, 67

22 Microwave source morphologies Loop (LF) + footpoints (HF): Nindos et al. 2000, ApJ 533, 1053 Compact loop : Kundu et al. 2001, ApJ 547, GHz SXR+HXR Multiple sources : footpoints (cospatial 17 GHz, HXR) compact or extended loops Nishio et al. 1997, ApJ 489, 976 Hanaoka 1996, 1997, Solar Phys.

23 Microwaves from solar flares are gyrosynchrotron rad. Co-evolution with HXR, gamma-ray continuum; electron acceleration to MeV energies (from 100 eV in the corona) within a few seconds. Electron spectrum consistent with that inferred from the gamma-ray continuum (NOT HXR continuum: mildly relativistic electrons !) Further reading : Bastian, Benz, Gary 1998 ARAA 36, 131; Pick, Klein, Trottet 1990 ApJS 73, 165; Benka & Holman 1994 ApJ 435, 469) Gyrosynchrotron radiation from solar flares : summary

24 Particle acceleration and magnetic reconnection Hard X-ray and radio bursts, and a cartoon scenario

25 Particle acceleration in a simple flare A set of complementary observations of EM emissions from flare-accelerated electrons : –Hard X-rays (h > 20 keV): energy spectra and imaging –Radio emission : spectra and imaging from ground (400 GHz > > 20 MHz) –Radio emission : spectra from space ( < 14 MHz) Vilmer et al Solar Phys 210, min

26 Hard X-ray emission from electron beams e beam HXR Image EUV TRACE / NASA Beam of suprathermal electrons travelling downward through the corona. Collisions with ambient protons : bremsstrahlung, h < energy(e) Particularly efficient when ambient density high (chromosphere) : frequently observed ‘footpoint’ sources at h >20 keV.

27 RHESSI HXR + TRACE : Krucker et al ApJ 678, L63 Hard X-ray emission from electron beams Beam of suprathermal electrons travelling downward through the corona. Collisions with ambient protons : bremsstrahlung, h < energy(e) Particularly efficient when ambient density high (chromosphere) : frequently observed ‘footpoint’ sources at h >20 keV. Low energy e deposit their E in the corona.

28 Particle acceleration in a simple flare A set of complementary observations of EM emissions from flare-accelerated electrons : –Hard X-rays (h > 20 keV): energy spectra and imaging –Radio emission : spectra and imaging from ground (400 GHz > > 20 MHz) –Radio emission : spectra from space ( < 14 MHz) Vilmer et al Solar Phys 210, min

29 1) Electromagnetic waves 2) Langmuir waves = electron plasma oscillations (ES waves, cannot exist in vacuum): … but can couple to EM waves and than escape from the source (cf. solar radio bursts) ω ω/k=cω/k=c k ω pe EM wave Langmuir wave High-frequency waves in a plasma : isotropic case (B=0)

30 Beam of suprathermal electrons travelling through the corona “Bump in tail” instability  f/  // > 0 : growth of Langmuir waves,  pe  n e Plateau (quasi-linear relaxation) Maxwellian Beam  // f(  // ) The Langmuir waves cannot escape from the corona, but … Radio emission from electron beams

31 Electron beam rising into the corona  Langmuir waves at decreasing Coupling with ion sound waves ( S << L ) or Langmuir waves  EM waves at – T = L + S  L  pe “fundamental” – T = L + L = 2 L  2 pe “harmonic ” Short radio burst that drifts from high to low (“type III” burst) e beam Height (time) Frequency high n e high low n e low Radio emission from electron beams

32 Hard X-rays from the low atmosphere (chromosphere) - e precipitated downward to n e > cm -3, bremsstrahlung with ambient p, h

33 Particle acceleration associated with magnetic reconnection ? A simple scenario. Particle acceleration region in a reconnecting coronal current sheet. Electric fields :- plasma inflow (-V  B) - turbulence - termination shock (outflow/ambient plasma) Vilmer et al Solar Phys

34 Mechanisms of charged particle acceleration Extended CS cannot exist in the solar corona : instabilities (e.g., tearing), fragmentation. Also : pb with high particle fluxes. Numerous regions with small-scale E fields, X points, O points and (contracting) magnetic islands. Multiple acceleration sites embedded in coronal plasma sheets. Aschwanden 2002 SSR 101, 1

35 Non thermal electrons in the corona outside flares Hot plasma (17 & 5.7 GHz), non thermal electrons (164 MHz) electron beams in IP space ( ) kHz (1 day overview)  Quasi-continuous electron acceleration in an active region, origin of non-maxwellian particle populations in IP space ? 17 GHz Nobeyama5.7 GHz Irkutsk0.164 GHz Nançay ( kHz) WAVES/WIND 24 h Wind/WAVES

36 Outlook: solar radio telescopes for the future The ideal solar imaging radio telescope : broadband cm-m-,  R  above the photosphere, high cadence –The Frequency-Agile Solar Radio Telescope (FASR) 30 MHz-30 GHz –dm- : Chinese RH (underway) MHz –Nobeyama Radioheliograph 17 & 34 GHz (chromosphere/low corona - flares and quiescent) –Siberian Solar Radio Telescope Irkutsk 5 GHz (low corona) –Nançay Radioheliograph MHz (corona  0.5 R  ) General purpose synthesis arrays at m- –LOFAR, Europe : (200-30) MHz (NL; under construction/deployment) –MWA, Australia : (300-30) MHz (MIT-australian cooperation) –Solar use to be explored, under discussion Sub-mm-IR imaging at high cadence: SST; extend to FIR (space) Maintain whole Sun patrol instrumentation: flares mm-Dm-


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