X-ray emission from the base of a current sheet in the wake of a CME

TL;DR

This study observed a long-duration X-ray source above the solar limb following a CME, revealing thermal properties and energy content that suggest it could be the heating source for the associated current sheet, with novel imaging spectroscopy techniques employed.

Contribution

The paper introduces novel back-projection and visibility-based imaging spectroscopy methods for analyzing long-duration X-ray sources in solar post-CME events.

Findings

X-ray source temperature peaked at 10-11 MK

No non-thermal hard X-ray emission detected

Thermal energy exceeds that of the current sheet

Abstract

Following a CME which started on 2002 November 26, RHESSI, the Ramaty High Energy Solar Spectroscopic Imager, observed for 12 hours an X-ray source above the solar limb, at altitudes between 0.1 and 0.3 RS above the photosphere. The GOES baseline was remarkably high throughout this event. The X-ray source's temperature peaked around 10-11 MK, and its emission measure increased throughout this time interval. Higher up, at 0.7 RS, hot (initially >8 MK) plasma has been observed by UVCS on SoHO for 2.3 days. This hot plasma was interpreted as the signature of a current sheet trailing the CME (Bemporad et al. 2006). The thermal energy content of the X-ray source is more than an order of magnitude larger than in the current sheet. Hence, it could be the source of the hot plasma in the current sheet, although current sheet heating by magnetic reconnection within it cannot be discounted. To better characterize the X-ray spectrum, we have used novel techniques (back-projection based and visibility-based) for long integration (several hours) imaging spectroscopy. There is no observed non-thermal hard X-ray bremsstrahlung emission, leading to the conclusion that there is either very little particle acceleration occurring in the vicinity of this post- are X-ray source, or that either the photon spectral index would have had to be uncharacteristically (in flare parlance) high (gamma >= 8) and/or the low-energy cutoff? very low (Ec <= 6 keV).