Measurements of the Super-Hot Flare Component and Reconnection Region Using the Fe XXV and Fe XXVI Lines

Near 1.8 Å

byGeorge Doschek

Presented at the 10th RHESSI Workshop – Planning a New

Mission, Contributed Instrument Concepts

5-6 August, Annapolis, MD 2010

Drake et al. 2006, 443, 553

Temperatures?Densities?Turbulence?Anisotropic Velocities?Spatial Scale Distributions?

Observing the Super-Hot Flare Component and the Flare Reconnection Region

• Some estimates are available for the physical parameters of the super-hot component: temperature, density estimate based on volume, emission measure, time history and flare class association from RHESSI (e.g., Amir Caspi) and Hinotori (e.g., K. Tanaka).

• But basically nothing is known about the physical characteristics in the flare reconnection region (it’s dark!)

• The superhot plasma parameters can be improved by high resolution spectroscopy, and physical parameters in the reconnection region can be determined for the first time.

Physical Conditions in the Accelerated Particle Region

• Temperatures > ~20 x 106 K• Electron densities are about 2 x 109 – 2

x 1011 cm-3 – Densities are based on EMs and observed

spatial volumes (RHESSI)– Filling factors are “uncertain”

• Emission Measures (EM) are about 1047 cm-3

• Volumes are about 1027 cm3

Necessary Spectrometer Instrument Characteristics for Measuring Physical

Parameters in the Flare Acceleration Region

• The spectrometer must be sensitive to temperatures in the range 20 – 100 MK.– The hottest lines in the EUV are Fe XXIV lines at

192 and 255 Å with a temperature range from about 10 – 20 MK. So can’t use EUV imagers.

• The spectrometer must be able to observe at or near flare onset.– This is difficult at present for any high resolution

imager.• The spectrometer must be capable of high

time resolution observations at or close to flare onset (~3 – 10 s).

Solar Flare Iron Spectra

Bragg Crystal Spectrometers

• Currently, only Bragg crystal spectrometers can satisfy the above conditions.– The spectral target must be the Fe XXVI (H-

like) and Fe XXV (He-like) resonance lines near 1.8 Å along with their innershell excited and dielectronic satellite lines.

• The above requirements can be satisfied with flat, bent, and/or imaging Bragg spectrometers. Imaging is highly desirable.

Solar Non-Imaging Bragg Crystal Spectrometers

BCS/FCS – Solar Maximum Mission (NASA)Hinotori – Japanese solar physics programP78-1 – US DoD Space Test Program

λ = 2d sin θ

Yohkoh/BCS

Solar Imaging Bragg Crystal Spectrometers

Mg XII, 8.42 Å

Fe XI, 175 Å

CORONAS-FZhitnik et al. 2003, MNRAS, 338, 67

Plasma Diagnostics from Bragg Spectrometers

• Electron temperature– From dielectronic to resonance line ratios– Independent of ionization equilibrium

• Electron density– From ionization times– From ionization equilibrium conditions

• Flows and Turbulence– From line profiles & wavelength shifts

• Polarization– From line ratios

• Non-Maxwellian Velocity Distributions

An Example of a New and Improved Yohkoh/BCS Spectrometer for Fe XXV and Fe XXVI

• This instrument has a factor of 10 more sensitivity than Yohkoh/BCS.• Eight crystals cover the Fe XXV complex and eight crystals cover the Fe XXVI

complex.• Ge 220 (2d = 4 Å) are used with sizes equal to Yohkoh/BCS.• Two crystals are oriented with wavelength increasing in the east/west direction;

two crystals are oriented with wavelength increasing in the west/east direction. The same for four crystals that are oriented in the north/south direction.

• Each crystal has its own position sensitive proportional counter detector.• The entrance filters are unchanged from Yohkoh/BCS.• The wavelength range of the Fe XXV crystals is 1.835 – 1.894 Å.• The wavelength range of the Fe XXVI crystals is 1.7636 – 1.8044 Å.• The entire instrument is pointed at an active region center and must be able to

track it with about 2” accuracy; the short and long wavelength ranges have about a 5’ slack to cover varying flare positions in the active region.

• A context TRACE-like instrument that images 171 and 195 Å filter bands is desirable but not necessary. SDO provides the filter information with its 132 Å band. SDO/EVE provides spectral context at low temperatures.

• Current NRL thinking is that a flat crystal spectrometer approach might be preferable to a bent crystal approach for a number of reasons. The above instrument is just an example of how to improve the previously flown Bragg instrument sensitivity and obtain more diagnostic capability.

5 January 1992 Flare: Yohkoh BCS Ca XIX (S11, E10)

BCSonset

Yohkoh BCS Ca XIX

Hist: BCS onsetThin solid: peak flux profileDashed: later rise phaseThick solid: average onset

5 January 1992 Flare

Physical Characteristics at BCS Flare Onset