Multiwavelength Stereoscopic Observation of the May 1, 2013 Solar Flare and CME

TL;DR

This study used multiwavelength stereoscopic observations to analyze a behind-the-limb solar flare and CME, revealing details about the hot plasma and non-thermal electron populations in the event.

Contribution

It provides new insights into the spatial and thermal structure of the CME and flare, especially the hot core and non-thermal electron distribution, using combined observations from multiple spacecraft.

Findings

Detected a hot, extended CME core with densities around 10^9 cm^-3.

Identified non-thermal X-ray sources above the CME core, indicating electron acceleration regions.

Found that high coronal hard X-ray sources are common in solar eruptions.

Abstract

A M-class behind-the-limb solar flare on 1 May 2013 (SOL2013-05-01T02:32), accompanied by a ($\sim$ 400 km/s) CME was observed by several space-based observatories with different viewing angles. We investigated the RHESSI-observed occulted hard X-ray emissions that originated at least 0.1 \solrad{} above the flare site. Emissions below $\sim$10 keV revealed a hot, extended (11 MK, >60 arcsec) thermal source from the escaping CME core, with densities around $10^{9}$ cm$^{-3}$. In such a tenuous hot plasma, ionization times scales are several minutes, consistent with the non-detection of the hot CME core in SDO/AIA's 131 \AA{} filter. The non-thermal RHESSI source originated from an even larger area ($\sim$100 arcsec) at lower densities ($10^{8}$ cm$^{-3}$) located above the hot core, but still behind the CME front. This indicates that the observed part of the non-thermal electrons are not responsible for heating the CME core. Possibly the hot core was heated by non-thermal electrons before it became visible from Earth, meaning that the un-occulted part of the non-thermal emission likely originates from a more tenuous part of the CME core, where non-thermal electrons survive long enough to became visible from Earth. Simultaneous hard X-ray spectra from the Mars Odyssey mission, which viewed the flare on disk, indicated that the number of non-thermal electrons $>$20 keV within the high coronal source is $\sim$0.1 - 0.5\% compared to the number within the chromospheric flare ribbons. The detection of high coronal hard X-ray sources in this moderate size event suggests that such sources are likely a common feature within solar eruptive events.