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.