ISSI International Team

Coronal Hard X-ray Sources in Solar Flares

Yohkoh observations of the Masuda flare of 1992 January 13. Left, soft X-ray whole-Sun image; Right, magnified soft X-ray image with hard X-ray contours and a sketch of the common interpretation of the observed features.

Scientific Aims - Proposal - Team Members - Meetings - Overview paper - Library - Notes

Our Review paper is accpeted (June 2008) and will appear in A&A Rev (2008 or 2009).

The final version of the review paper is on line here.

Publications that benefited from this workshop:

1) Krucker Säm, Battaglia M., Cargill P.J., Fletcher L., Hudson H.S, MacKinnon, A.L., Masuda S., Sui L., Tomczak T., Veronig A.M., Vlahos l., White S.M.; Hard X-ray emission from the solar Corona, A&A Rev, 2008, in press

2) Tomczak, M.; Ciborski, T.: Footpoint versus loop-top hard X-ray emission sources in solar flares, A&A, 461, 315, 2007

3) Krucker, Säm; White, S. M.; Lin, R. P.: Solar Flare Hard X-Ray Emission from the High Corona, ApJL, 669, L49, 2007

4) Krucker Säm, & Lin R.P., 'Hard X-Ray Emissions from Partially Occulted Solar Flares', ApJ, 673, 1181, 2008

5) Battaglia, M.; Benz, A.O.: Observational evidence for return currents in solar flare loops, A&A, 487, 337, 2008

6) Krucker, Säm; Hurford, G.J.; MacKinnon, A.L.; Shih, A.Y.; Lin, R.P., 'Coronal Gamma-Ray Bremsstrahlung from Solar Flare-accelerated Electrons', ApJL, 678, L63, 2008

7) Krucker, Säm; Saint-Hilaire, P.; Christe, S.; White, S. M.; Chavier, A. D.; Bale, S. D.; Lin, R. P.: Coronal Hard X-Ray Emission Associated with Radio Type III Bursts, ApJ, 681, 644, 2008

Scientific Aims

Coronal hard (>20~keV) X-rays differ fundamentally from the 'footpoint' emission normally seen in solar flares and exhibit a wider array of properties. The corona should not generally be a strong bremsstrahlung source because of its low plasma density, but the observation of limb-occulted events such as that of 30~March 1969 (Frost & Dennis 1971) contradicted this expectation. While hard X-ray footpoint emissions show where flare-accelerated electrons lose their energy, coronal hard X-ray sources might reveal emission from the acceleration site itself. Coronal hard X-ray observations therefore provide a great diagnostic tool for particle acceleration in solar flares. Now we can image these sources and also determine their spectra in some detail, using the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) observations. Neither these data nor those of the earlier Yohkoh observations have been treated systematically in the literature. Accordingly we plan to write one overview paper setting out the range of observations and interpretations derived from our discussions. Furthermore, we will relate these observations to each other, discuss their relationship and implications.


Original proposal for the CornSource team (pdf file)

Team Members

Säm Krucker (team leader), UC Berkeley, USA
Hugh Hudson (team leader), UC Berkeley, USA
Peter Cargill, Imperial College, UK
Lyndsay Fletcher, U. of Glasgow, UK
Takeo Kosugi
Alec MacKinnon, U. of Glasgow, UK
Satoshi Masuda, STELab, Japan
Linhui Sui, NASA, USA
Michal Tomczak, U. of Wroclaw, Poland
Astrid Veronig, U. of Graz, Austria
Loukas Vlahos, U. of Thessaloniki, Greece
Steven White, U. of Maryland, USA


First: October 3-6, 2006 (see below for links to presentations)
Second: May 8-11, 2007 (Tue - Fri)

Second meeting (draft schedule):

AM1 9:00 - 10:30 AM2 11:00 - 12:30 PM1 2:00 - 3:30 PM2 4:00 - 5:30


Alec MacKinnon: Mechanisms for generating HXRs New RHESSI results: Marina Battaglia (ETH Zurich), Sui, Veronig, Krucker New Yokhoh results Masuda, Tomczak update: Radio observations (White) update: multi-wavelength observations (Fletcher) update: theory (Cargill/Vlahos)

discussion of first draft of review paper
discussion & editing of first draft

discussion & editing of first draft
Discussion of future data analyses finishing second draft by the end of the day

discussion of second draft discussion on how to finish paper

Presentations (from first meeting)

Hudson (history, pre-RHESSI) click here
Masuda (Masuda flare) click here
Tomczak (Yohkoh statistical studies) click here
White (Radio observations) click here
Fletcher (Multi-wavelength) click here
Sui (Low energy and thermal sources) click here
Veronig (thick target in the corona) click here
Krucker (Review: RHESSI observations of coronal sources) click here
Cargill (theory) click here
Vlahos (theory) click here

Overview paper

The working material for the projected review paper is on line here. Please just check the dates of the files to see how current the version is. Since this is a group effort, please feel free to work on anything and make contributions. To avoid confusion, please coordinate any Tex input with Hugh so that we don't have multiple versions floating around. These should probably be restricted to whole discrete sections rather than to "wordsmithing" - for the latter, please just send the .pdf file back marked up, or a simple email (to Hugh and Säm).

Some pretty pictures:


We are accumulating .pdf files for relevant literature here for convenience. Please add papers you like and/or ask for them to be added. At Loukas's suggestion we will separate these into groups based on which presentation they are associated with, and perhaps have a general alphabetical listing as well. Note added March 12, 2007: This of course has not been working out very well. However please note that the file "files/chx.bib" to be found at the draft overview directory has many citations, each with its ADS link.


Informal Notes on discussions, ie things outside the presentation materials.

Picture gallery

Gallery A few pictures from the each meeting, including one bear from the first meeting. Send other pictures if you would like to show them off.)