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Coronal HXR sources

Coronal HXR sources. a multi-wavelength perspective. Why use multi-wavelength?. Plasma properties of HXR-emitting volume Relationship to other sources Relationship to overall flare configuration / evolution. Diagnostics available:

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Coronal HXR sources

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  1. Coronal HXR sources a multi-wavelength perspective

  2. Why use multi-wavelength? • Plasma properties of HXR-emitting volume • Relationship to other sources • Relationship to overall flare configuration / evolution Diagnostics available: Line ratios  temperature, density (at line formation temperature) Filter ratios  temperature Emission measures  density (for assumed/measured vol.) Line widths/shifts  bulk and ‘non-thermal’ speeds

  3. 50-100 keV 20-30 keV 30-50 keV GOES & RHESSI One example (Bone et al. 2005) of an occulted flare GOES emission measure and RHESSI ‘volume’ provide an estimate of coronal source density. in this event gives n ~ 1011cm-3

  4. TRACE filter ratio Warren & Reeves 2001 Temperature diagnostic formed with TRACE 195/171 channels (uses Fe XXIV in 195, and cont. bremsstrahlung in 171) Red areas consistent with T>20MK, low FIP elements 5x photosphere. (CHIANTI v3) Phillips et al. 2005 RHESSI 6-12keV co-spatial with hot TRACE loops.

  5. Timing analysis Aschwanden & Alexander 2001 analysis of loop emission in Bastille Day 2000 flare Emission integrated over whole FOV of each instrument All curves show are predominantly arcade emission. Calculate contribution function for each instrument – determine primary temperature of each filter Cooling initially by conduction (t<200s) then radiation

  6. CDS observations – few and far-between Berlicki et al – Fe XIX (8MK) ~ co-spatial with RHESSI coronal source. - both are hot….. No published examples of CDS density or temperature line-ratio diagnostics of flares. (co-ordinated observations are rare, also diagnostic ratios compromised post-1998 SOHO recovery)

  7. CDS velocity measurements a few velocity measurements available for footpoint sources in both impulsive and decay phase of flares. ‘Typically’ – downflow ~ 10s of km/s in ‘chromospheric’ lines upflows ~ 100km/s in lines at 2-6MK (Brosius 03) What about flare coronal measurements? Milligan et al 06 – possibly high T blue-shifted emission in a coronal loop? v ~ 100-200km/s

  8. UVCS Lin et al 2005 Lya – ion density (assuming neutrals coupled to p+) @1.7R dense coronal regions move inwards to less-dense region Interpreted as plasma inflows ~ 10-100km/s Ciaravella et al 2002 narrow feature in UVCS slit 6.3MK @ 2.55 R ne ~ 6 107cm-3 Non-thermal line-width < 60km/s

  9. April 21 2002 – RHESSI’s first X-class event Extended coronal HXR source appears early on, before high energy footpoints and 4min before TRACE 195 channel emission. Gallagher et al 2002 suggest coronal energy release directly heats plasma to > 20MK, then it cools down.

  10. SUMER observations April 21 2002 event – Innes, McKenzie & Wang 2003 Vertical white line = SUMER slit position Observations in CII, FeXII, Fe XXI Contribution functions  pretty good temperature coverage Also, UV continuum emission gives info on bremsstrahlung

  11. Also at Doppler shifts to blue, up to 1000km/s in FeXXI, observed at time that ‘voids’ reach same location Voids are dark in all 3 emission lines observed. Continuum emission implies low EM in voids (rather than absorption by dense cold gas) Conclusion – voids are empty.

  12. Voids & HXRs in 23-Jul-02 Asai et al 2004 Not such a clear example BUT downflows seen also in impulsive and main phase. Evolution of TRACE 195A intensity along slit, as function of time (reverse colour) Claim: times of void ‘descent’ corresponds to peaks seen in RHESSI/NoRH (Also seen in work with SXT/HXT by Khan et al. 2006) 50-100keV

  13. line centre red wing red wing red wing line centre red wing line centre line centre Relationship to Ha loops – erupting case Veronig et al 2006 Ha loop density ~ 1012cm-3 RHESSI (early), n ~ 1010cm-3 RHESSI/GOES (late) n ~ 1011cm-3 High T emission above low T Ha loops at lower altitudes than HXR source / EUV / SXR loops

  14. HXR-Ha failed eruption Ji et al 2003 – high cadence Ha blue wing observations Filament does not escape, returns to surface. HXRs/EUV emission close to location where filament ‘ruptures’ Ha EUV 12-25keV RHESSI

  15. White-light coronal source Hudson et al 2006, Fletcher et al 2006 observe a coronal source in TRACE white-light and 1700Å, and RHESSI 25-50keV. Also see work of Leibacher et al. using broad-band ground-based WL. This kind of source (exceeding photospheric surface brightness) may imply a very high coronal density. WL emission mechanism unclear.

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