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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 0.327 GHz / 91 cm Karl-Ludwig Klein Observatoire de Paris - Meudon Ludwig.klein@obspm.fr

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 0.327 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 252004 Jun 272004 Jun 282004 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] 10 6 10 5 Wavelength [m] 120.6 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 http://www.ovsa.njit.edu/fasrhttp://www.ovsa.njit.edu/fasr 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. 2002 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. 1998 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, 1090 17 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. 2002 Solar Phys 210, 261 5 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. 2008 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. 2002 Solar Phys 210, 261 5 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 > 10 12 cm -3, bremsstrahlung with ambient p, h { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/4072743/13/slides/slide_31.jpg", "name": "Hard X-rays from the low atmosphere (chromosphere) - e precipitated downward to n e > 10 12 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. 2002 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 (1000-20) 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 (20-1000 kHz) WAVES/WIND 24 h Wind/WAVES

36 Outlook: solar radio telescopes for the future The ideal solar imaging radio telescope : broadband cm-m-,  0.01-1 R  above the photosphere, high cadence –The Frequency-Agile Solar Radio Telescope (FASR) 30 MHz-30 GHz –dm- : Chinese RH (underway) 400-1600 MHz –Nobeyama Radioheliograph 17 & 34 GHz (chromosphere/low corona - flares and quiescent) –Siberian Solar Radio Telescope Irkutsk 5 GHz (low corona) –Nançay Radioheliograph 450-150 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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