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

<jats:title>Abstract</jats:title> <jats:p>A M-class behind-the-limb solar flare on 2013 May 1 (SOL2013-05-01T02:32), accompanied by a (∼400 km s<jats:sup>−1</jats:sup>) coronal mass ejection (CME), was observed by several space-based observatories with different viewing angles. We investigated the <jats:italic>RHESSI</jats:italic>-observed occulted hard X-ray (HXR) emissions that originated at least 0.1 <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{{\rm{S}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab4a0aieqn1.gif" xlink:type="simple" /> </jats:inline-formula> above the flare site. Emissions below ∼10 keV revealed a hot, extended (11 MK, >60″) thermal source from the escaping CME core, with densities around 10<jats:sup>9</jats:sup> cm<jats:sup>−3</jats:sup>. In such a tenuous hot plasma, ionization times scales are several minutes, consistent with the nondetection of the hot CME core in <jats:italic>SDO</jats:italic>/AIA’s 131 Å filter. The nonthermal <jats:italic>RHESSI</jats:italic> source originated from an even larger area (∼100″) at lower densities (10<jats:sup>8</jats:sup> cm<jats:sup>−3</jats:sup>) located above the hot core, but still behind the CME front. This indicates that the observed part of the nonthermal electrons are not responsible for heating the CME core. Possibly the hot core was heated by nonthermal electrons before it became visible from Earth, meaning that the unocculted part of the nonthermal emission likely originates from a more tenuous part of the CME core, where nonthermal electrons survive long enough to became visible from Earth. Simultaneous HXR spectra from the <jats:italic>Mars Odyssey</jats:italic> mission, which viewed the flare on disk, indicated that the number of nonthermal electrons >20 keV within the high coronal source is ∼0.1%–0.5% compared with the number within the chromospheric flare ribbons. The detection of high coronal HXR sources in this moderate size event suggests that such sources are likely a common feature within solar eruptive events.</jats:p>