RHESSI and the Solar RHESSI and the Solar Flare X-ray SpectrumFlare X-ray Spectrum

Ken PhillipsKen Phillips

Presentation at Wroclaw Workshop “X-ray spectroscopy and plasma diagnostics from the RESIK, RHESSI and SPIRIT Instruments “, December 6—8, 2005

Reuven Ramaty High Reuven Ramaty High Energy Solar Spectroscopic Energy Solar Spectroscopic Imager Imager (RHESSI) (RHESSI)

RHESSI Launch from RHESSI Launch from PegasusPegasus

Launch of RHESSI:

Feb. 5, 2002

Pegasus rocket carrying RHESSI

NASA plane

RHESSI Spacecraft RHESSI Spacecraft ConceptConcept

SUN

S/C Rotates

RHESSI’s Energy RangeRHESSI’s Energy Range

• RHESSI observes soft and hard X-ray RHESSI observes soft and hard X-ray emission up to gamma-rays: 4 keV emission up to gamma-rays: 4 keV up to 17 MeVup to 17 MeV

• Conversion is Conversion is

λλ(Å) = 12.4 / E (keV)(Å) = 12.4 / E (keV)

RHESSI 10—25 keV RHESSI 10—25 keV images ofimages of near-limb flare near-limb flareLinHui Sui & Holman 2003

Spatial resolution in these images 7 arcsec (can be as good as 2 arcsec)

Solar Limb

Holman et al. (2002) -- HXR and Gamma-ray images -- RHESSI, 2002 July 23 flare

Gamma rays

HXR emission

SOHO/MDI magnetogram

TRACE and RHESSI Flare TRACE and RHESSI Flare Images Images

RHESSI as a Spectrometer: RHESSI as a Spectrometer:

Spectral Resolution Spectral Resolution

..• Spectral resolution best for RHESSI Spectral resolution best for RHESSI

Detectors 3 and 4: 1 keV at ~ 7 keVDetectors 3 and 4: 1 keV at ~ 7 keV

or ~0.25or ~0.25Å at 1.9Å.Å at 1.9Å.

• Spectral resolution “broad-band”, not Spectral resolution “broad-band”, not like crystal spectrometer resolution.like crystal spectrometer resolution.

• RHESSI sees Fe XXV lines and satellites RHESSI sees Fe XXV lines and satellites as a single “bump” on continuum.as a single “bump” on continuum.

• However, RHESSI does see the However, RHESSI does see the continuum (whereas crystal continuum (whereas crystal spectrometers usually affected by spectrometers usually affected by crystal fluorescence).crystal fluorescence).

RHESSI flare RHESSI flare spectrumspectrum

Flare X-ray SpectraFlare X-ray Spectra

• Electrons accelerated at reconnection Electrons accelerated at reconnection site travel from loop top to site travel from loop top to chromosphere, producing X-ray emission chromosphere, producing X-ray emission with with nonthermalnonthermal spectrum (hv > 20 spectrum (hv > 20 keV). keV).

• Material in previously empty loop filled Material in previously empty loop filled with heated plasma (T~20MK) that with heated plasma (T~20MK) that produces a produces a thermalthermal spectrum (hv < 20 spectrum (hv < 20 keV) consisting of keV) consisting of lineslines and and continuumcontinuum..

Two Line Two Line featuresfeatures in in RHESSI RHESSI spectra spectra6.7 keV or “Fe line feature”6.7 keV or “Fe line feature”

– Fe XXV linesFe XXV lines– Fe XVIII – Fe XXIV satellitesFe XVIII – Fe XXIV satellites– Fe XXVI lines at higher T (>80MK) Fe XXVI lines at higher T (>80MK) – Seen with crystal spectrometersSeen with crystal spectrometers

8 keV or “Fe/Ni line feature”8 keV or “Fe/Ni line feature”– More highly excited Fe XXV,Fe XXVI More highly excited Fe XXV,Fe XXVI

lineslines– Ni XXVII, Ni XXVIII lines & satellitesNi XXVII, Ni XXVIII lines & satellites– Never seen with crystal Never seen with crystal

spectrometersspectrometers

Fe and Fe/Ni line Fe and Fe/Ni line features:features: RHESSI observations RHESSI observations

So RHESSI the first instrument (apart So RHESSI the first instrument (apart from NEAR-PIN) to see the 8 keV from NEAR-PIN) to see the 8 keV featurefeature

By analyzing the 2 line features, one By analyzing the 2 line features, one can can diagnose the hottest partdiagnose the hottest part of the of the flare thermal plasmaflare thermal plasma

Chianti Chianti Spectrum,T=20MKSpectrum,T=20MK

Fe XXV +satellitesNi XXVII + sats

Ca XIX

Fe XXV

Fe edge

Fe XXV

Fe XXVI

Chianti spectra + spectraChianti spectra + spectra smoothed to RHESSI smoothed to RHESSI resolutionresolution

SMM/BCS Fe line flare SMM/BCS Fe line flare spectraspectra

Fluorescence background

Synthetic (CHIANTI) Synthetic (CHIANTI) spectra,spectra, solar plasma (8-33 MK) solar plasma (8-33 MK)

RHESSI (1 keV) resolution assumed

Chianti: coronal abund. + Mazzotta et al. ion. eq.

Lines making up the `Fe-Lines making up the `Fe-line’ line’ (6.7 keV) feature (6.7 keV) feature

Lines making up the Lines making up the `Fe/Ni’ `Fe/Ni’ (8 keV) feature (8 keV) feature

Solar flare spectrum, Solar flare spectrum, NEAR-NEAR- PIN and Yohkoh/BCS PIN and Yohkoh/BCS

NEAR-PIN: R. Starr

Yohkoh: S, Ca, Fe channels

NEAR-PIN

BCS

Fe line (6.7 keV) Fe/Ni

line (8 keV)

S XV

Ca XIX

Element (e.g. Fe) Element (e.g. Fe) AbundancesAbundances

• With measurement of line and With measurement of line and continuum flux, we can measure continuum flux, we can measure element abundances element abundances

• Thus, with 6.7 keV (“Fe line”) Thus, with 6.7 keV (“Fe line”) feature, we can measure Fe/H.feature, we can measure Fe/H.

• Use equivalent width of line to do Use equivalent width of line to do this.this.

Emission Line Equivalent Emission Line Equivalent WidthWidth Definition Definition

Energy (keV)

Equivalent Width of the Fe Equivalent Width of the Fe lineline

Based on Chianti v. 5.1, coronal abundances and Mazzotta et al. ion fractions

(This plot is different from Phillips 2004)

RESIK in 3rd order

Attenuator states

Theoretical curve (Phillips 2004) based on coronal Fe abundance and Mazzotta et al. ion fractions

FFee

Theoretical curve

Equivalent Width PlotsEquivalent Width Plots

• April 23, 2003 flare is `good’ example April 23, 2003 flare is `good’ example – plenty of not-so-good examples!– plenty of not-so-good examples!

• There are problems associated with There are problems associated with high count rates in the A0 attenuator high count rates in the A0 attenuator state and in the A3 attenuator state – state and in the A3 attenuator state – these are not understood at present. these are not understood at present.

• Cristina will show more examples….Cristina will show more examples….

• Tentative conclusion: flare Fe Tentative conclusion: flare Fe abundance ~ coronal Fe abundance abundance ~ coronal Fe abundance (Feldman & Laming 2000)(Feldman & Laming 2000)

Fe XXIV/Fe XXV Ion Fe XXIV/Fe XXV Ion Fractions wrong?Fractions wrong?

• In CHIANTI analysis, we used Mazzotta et In CHIANTI analysis, we used Mazzotta et al. (1998) ion fractions – maybe slightly al. (1998) ion fractions – maybe slightly wrong?wrong?

• No measured rates for these ions, so No measured rates for these ions, so everything relies on calculationseverything relies on calculations

• There are some ‘measured’ rates from There are some ‘measured’ rates from SMM/BCS flare spectra: Fe XXIV satellites (j SMM/BCS flare spectra: Fe XXIV satellites (j and q) / Fe XXV w line ratios (Antonucci et and q) / Fe XXV w line ratios (Antonucci et al.)al.)

RHESSI and RHESSI and CORONAS-F/RESIKCORONAS-F/RESIK Solar Flare Spectra Solar Flare Spectra

• Both RHESSI and RESIK Both RHESSI and RESIK spectrometers carefully calibrated – spectrometers carefully calibrated – estimated uncertainties ~20%estimated uncertainties ~20%

• Useful to compare spectra for same Useful to compare spectra for same times in flares – agreement very times in flares – agreement very good. good.

• RESIK 1RESIK 1stst-order spectra agree with -order spectra agree with the low-energy end of RHESSI the low-energy end of RHESSI spectra.spectra.

Plotting spectra from 7 Plotting spectra from 7 RHESSI detectors + RESIKRHESSI detectors + RESIK

Summary and Summary and ConclusionsConclusions• RHESSI a `broad-band’ spectrometer, RHESSI a `broad-band’ spectrometer,

sees both thermal and nonthermal sees both thermal and nonthermal spectra of solar flares (sp. res. 1 keV).spectra of solar flares (sp. res. 1 keV).

• RHESSI sees two line features, at 6.7 RHESSI sees two line features, at 6.7 keV (Fe) and 8 keV (Fe/Ni).keV (Fe) and 8 keV (Fe/Ni).

• Line equivalent widths mostly indicate Line equivalent widths mostly indicate coronal abundance of Fe.coronal abundance of Fe.

• Possibly ionization fractions of Fe XXV Possibly ionization fractions of Fe XXV need revision.need revision.