1 / 36

The Radio Sun

VLA 1.4 GHz / 21 cm. NoRH 17 GHz / 1.8 cm. NRH 0.327 GHz / 91 cm. The Radio Sun. Karl-Ludwig Klein Observatoire de Paris - Meudon Ludwig.klein@obspm.fr. The solar corona. Magnetograms - SoHO/MDI. EUV images - SoHO/EIT.

diane
Download Presentation

The Radio Sun

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. VLA 1.4 GHz / 21 cm NoRH 17 GHz / 1.8 cm NRH 0.327 GHz / 91 cm The Radio Sun Karl-Ludwig Klein Observatoire de Paris - Meudon Ludwig.klein@obspm.fr

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

  3. Radio observations of the solar atmosphere VLA 1.4 GHz / 21 cm NoRH 17 GHz / 1.8 cm NRH 0.327 GHz / 91 cm • Radio waves from the solar atmosphere : • propagation at  >pe ne decreases with increasing altitude • sounding of different heights at different frequencies (0 RS-1 AU) • Emission processes 1 : thermal plasma • free-free • gyroresonance (enhanced opt depth at  = sce; s=2, 3, 4)

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

  5. Solar radio astronomy in Europe

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

  7. Observations of the solar corona at radio  • Plasma diagnostics of the corona (ne, 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

  8. Observations of the solar corona at radio  • Plasma diagnostics of the corona (ne, 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

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

  10. 2004 Jun 25 2004 Jun 27 2004 Jun 28 2004 Jun 29 + - h A multi frequency view of the radio Sun Nançay Radioheliograph 410 MHz Siberian Solar Radio Telescope 5.7GHz Nobeyama Radioheliograph 17 GHz Different structures at : active regions (GHz), coronal holes

  11. Coronal plasma parameters Nançay Radioheliograph 106 Tb (average corona) Tb (coronal hole) Brightness temperature [K] 105 0.6 1 2 Wavelength [m] Bremsstrahlung: brightness spectrum depends on ne & Te Low  : Tb = Te = 6.7105 K High  : Tb << Te ne = 2.3108 cm-3 Mercier & Chambe 2009 ApJ 700, L137

  12. Intensity Time Frequency Gyromagnetic radiation B • Electron cyclotron frequency • Low speed electron (T=106 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

  13.  =5 GHz, s=3  =8,4 GHz, s=3  >3ce,max chromosphère 1000 G 600 G =sce (s=2 … 4 for Te2106K) -> 5 GHz (6 cm) if s=3, B=600 G Resonant surf., depth ~100 km Gyroresonance emission: a tool for coronal magnetic field measurements • Gyroresonance emission

  14. Gyroresonance emission: a tool for coronal magnetic field measurements Optical + VLA • gr>1 : Tb 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. 1998, ApJ 501, 853 Lee et al. 1999, ApJ 510, 413

  15. Thermal radio emission from the solar corona: summary • The corona emits bremsstrahlung at cm-to-m- (quiet corona), optically thin or thick. • Determination of coronal plasma parameters from bremsstrahlung spectrum (ne, Te); 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/fasr

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

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

  18. Gyrosynchrotron interpretation Opt. thick Opt. thin Observations : Owens Valley, Nita, Gary, Lee 2004, ApJ 605, 528 • 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

  19. Trottet et al. 2002 A&A Relativistic electrons at the Sun • Solar radio burst : usually observed up to some tens of GHz. • New: =212 GHz (SST1): synchrotron emission from relativistic e-:  =10 • Slope of the microwave spectrum (1) Univ. Mackenzie Sao Paulo

  20. Relativistic electrons at the Sun • 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 )

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

  22. 17 GHz SXR+HXR Microwave source morphologies Loop (LF) + footpoints (HF): Nindos et al. 2000, ApJ 533, 1053 Compact loop : Kundu et al. 2001, ApJ 547, 1090 • Multiple sources : • footpoints (cospatial 17 GHz, HXR) • compact or extended loops • Nishio et al. 1997, ApJ 489, 976 • Hanaoka 1996, 1997, Solar Phys.

  23. Gyrosynchrotron radiation from solar flares : summary • 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)

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

  25. 5 min 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

  26. Hard X-ray emission from electron beams HXR • 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. e beam Image EUV TRACE / NASA

  27. Hard X-ray emission from electron beams RHESSI HXR + TRACE : Krucker et al. 2008 ApJ 678, L63 • 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. 5 min 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

  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 EM wave ω/k=c Langmuir wave ωpe k High-frequency waves in a plasma : isotropic case (B=0)

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

  31. Radio emission from electron beams high ne low ne low  high  Frequency Height (time) e beam • 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)

  32. 5 min Particle acceleration in a simple flare • Hard X-rays from the low atmosphere (chromosphere) - e precipitated downward to ne > 1012 cm-3, bremsstrahlung with ambient p, h<energy(e). • Radio emission (type III) from outward propagating e beams, =2pene, start < 400 MHz : ne < 109 cm-3, energy ~10 keV.  Acceleration region in the corona, injects particles downward (chromosphere) & upward (high corona, IP space) Vilmer et al. 2002 Solar Phys 210, 261

  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. 17 GHz Nobeyama 5.7 GHz Irkutsk 0.164 GHz Nançay 24 h 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 ? Wind/WAVES (20-1000 kHz) WAVES/WIND

  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-

More Related