EIT and TRACE responses to flare plasma

Free access article

Issue		A&A Volume 460, Number 3, December IV 2006


Page(s)		L53 - L56
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20066481

A&A 460, L53-L56 (2006)
DOI: 10.1051/0004-6361:20066481

Letter

EIT and TRACE responses to flare plasma

D. Tripathi¹, G. Del Zanna², H. E. Mason¹, and C. Chifor¹

¹ Department of Applied Maths and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK
e-mail: [D.Tripathi;H.E.Mason;C.Chifor]@damtp.cam.ac.uk
² University College London, MSSL, Holmbury St. Mary Dorking Surrey RH5 6NT, UK
e-mail: gd232@mssl.ucl.ac.uk

(Received 29 September 2006 / Accepted 2 November 2006)

Abstract
Aims.To understand the contribution of active region and flare plasmas to the $\lambda$ 195 channels of SOHO/EIT (Extreme-ultraviolet Imaging Telescope) and TRACE (Transition Region and Coronal Explorer).
Methods.We have analysed an M8 flare simultaneously observed by the Coronal Diagnostic Spectrometer (CDS), EIT, TRACE and RHESSI. We obtained synthetic spectra for the flaring region and an outer region using the differential emission measures (DEM) of emitting plasma based on CDS and RHESSI observations and the CHIANTI atomic database. We then predicted the EIT and TRACE count rates.
Results.For the flaring region, both EIT and TRACE images taken through the $\lambda$ 195 filter are dominated by $\ion{Fe}{xxiv}$ (formed at about 20 MK). However, in the outer region, the emission was primarily due to the $\ion{Fe}{xii}$ , with substantial contributions from other lines. The average count rate for the outer region was within 25% the observed value for EIT, while for TRACE it was a factor of two higher. For the flare region, the predicted count rate was a factor of two (in case of EIT) and a factor of three (in case of TRACE) higher than the actual count rate.
Conclusions.During a solar flare, both TRACE and EIT $\lambda$ 195 channels are found to be dominated by $\ion{Fe}{xxiv}$ emission. Reasonable agreement between predictions and observations is found, however some discrepancies need to be further investigated.

Key words: Sun: corona -- Sun: activity -- Sun: flares -- techniques: spectroscopic

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