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:
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
20-30 keV 30-50 keV 50-100 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
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.
TRACE filter ratio
Timing analysisAschwanden & 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
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)
CDS observations – few and far-between
CDS velocity measurementsa 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
UVCS
Ciaravella et al 2002
narrow feature in UVCS slit
6.3MK @ 2.55 R
ne ~ 6 107cm-3
Non-thermal line-width < 60km/s
Lin et al 2005
Ly – 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
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.
April 21 2002 – RHESSI’s first X-class event
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
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.
Also at Doppler shifts to blue, up to 1000km/s in FeXXI, observed at time that ‘voids’ reach same location
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
Relationship to H loops – erupting case
Veronig et al 2006
High T emission above low T
H loops at lower altitudes than HXR source / EUV / SXR loops
line centre red wing
line centre
line centreline centre
red wingred wing
red wing
H loop density ~ 1012cm-3
RHESSI (early), n ~ 1010cm-3
RHESSI/GOES (late) n ~ 1011cm-3
HXR-H failed eruptionJi et al 2003 – high cadence H blue wing observations
Filament does not escape, returns to surface.
HXRs/EUV emission close to location where filament ‘ruptures’
H
EUV
12-25keV RHESSI
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.