EDP Sciences
Free access
Volume 489, Number 3, October III 2008
Page(s) L57 - L60
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200810719
Published online 11 September 2008

A&A 489, L57-L60 (2008)
DOI: 10.1051/0004-6361:200810719


Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop

E. P. Kontar1, I. G. Hannah1, and A. L. MacKinnon2

1  Department of Physics and Astronomy, University of Glasgow, G12 8QQ, UK
    e-mail: [eduard;iain]@astro.gla.ac.uk
2  Department of ACE, University of Glasgow, G12 8QQ, UK
    e-mail: alec@astro.gla.ac.uk

Received 30 July 2008 / Accepted 26 August 2008

Aims. A novel method of using hard X-rays as a diagnostic for chromospheric density and magnetic structures is developed to infer sub-arcsecond vertical variation of magnetic flux tube size and neutral gas density.
Methods. Using Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) X-ray data and the newly developed X-ray visibilities forward fitting technique we find the FWHM and centroid positions of hard X-ray sources with sub-arcsecond resolution (~0.2'') for a solar limb flare. We show that the height variations of the chromospheric density and the magnetic flux densities can be found with an unprecedented vertical resolution of ~150 km by mapping 18-250 keV X-ray emission of energetic electrons propagating in the loop at chromospheric heights of 400-1500 km.
Results. Our observations suggest that the density of the neutral gas is in good agreement with hydrostatic models with a scale height of around 140 $\pm$ 30 km. FWHM sizes of the X-ray sources decrease with energy suggesting the expansion (fanning out) of magnetic flux tubes in the chromosphere with height. The magnetic scale height B(z)(dB/dz)-1 is found to be of the order of 300 km and a strong horizontal magnetic field is associated with noticeable flux tube expansion at a height of ~900 km.

Key words: Sun: chromosphere -- Sun: flares -- Sun: X-rays, gamma rays -- Sun: magnetic fields -- Sun: activity

© ESO 2008

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.