Multi-wavelength targets for a new flare/CME/SEP mission

Lyndsay Fletcher

(University of Glasgow)

& wisdom of all of RHESSI WG4 2002-2010

Flare plasma spectroscopic diagnostics

The majority of of the flare radiative energy originates in the chromosphere and has a huge diagnostic potential SOHO/CDS and Hinode/EIS used for studies of chromospheric flare evaporation speeds.

Hinode/EIS can also be used for flare densities

One or two decent SOHO/SUMER flare observations!

We need a better understanding of density, temperature, velocity & turbulence structure during the flare

Chromospheric plasma diagnostics

- compare with predictions of radiative hydro models (cf quiet chromosphere)- understand where, when (and how?) chromospheric energy input happens- understand how optical continuum formed – photosphere or chromosphere?

One snapshot of an RHD flare model – heating by a time-varying electron beam (Allred et al 05)

In fact, most of the flare radiated power is in the optical and UV – comparatively little known about this observationally!

The best examples of broadband observations (Neidig 83, Hiei 82, Machado & Rust 74)(in here are the high order Balmer lines – can be used for Stark broadening measurements)

TRACE 1216 Å channel

Do we need arcsecond scales to understand flares? (Emslie)

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Imaging of footpoints

TRACE White light1” resolution, 2s cadence

- Correlations & context: Impulsive phase WL footpoints correlate in space and time with HXRs, and images show larger active region context.- Detail: from optical we know that footpoints are not simple! Optical imaging helps to interpret HXR measurements- Spatial scales – Hinode G-band observations -> brightest WL sources have sub arcsecond scales- Topology: UV ribbons/WL footpoints help decipher evolving coronal topology

Flare-CME relationship

Imaging – but what kind? Lyman alpha? Strong line but not hugely enhanced in a flare (no saturation issues). Shows ribbons and filament lift-off – study link between filament lift-off and flare

RHESSI lightcurves and SXR images pin down flare and beginning of CME eruption

- Simultaneous within 3 minutes.- Do we need to do this better?

Temmer et al (2008)

We need to understand the relationship between magnetic restructuring in the corona and particle acceleration

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Faint coronal HXR sources

With RHESSI, we are just scratching the surface of the ways in which a magnetised plasma can accelerate electrons! Need higher dynamic range

With RHESSI, we have seen a great variety of faint looptop X-ray sources, thermal and non-thermal; e.g. merging of downward propagating plasmoid and looptop.

From radio - there are far more subtle changes that accelerate electrons – e.g. decimetric spike bursts possibly caused by compression of corona

Khan & Aurass 2006

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Summary

Desirable observations for a multi-wavelength view of flares:

• UV and EUV spectroscopy for density, velocity, temperature, turbulence of chromospheric, TR and coronal flare plasmas

• Broad-band optical spectroscopy, as well as narrow band focussing on some lines with capacity to diagnose beam properties (e.g. H-Ca 8542) and Stark broadening (high order Balmer series)

• High time cadence (seconds) and high resolution (0.1-1”) optical and UV imaging – for footpoints and early phase of CME liftoff (also WL for co-alignment with ground-based)

• High dynamic range HXR imaging – at least to a few 10s of keV to probe link between coronal field restructuring and particle acceleration