Impulsive Phase Coronal Hard X-Ray Sources in an X3.9 Class Solar Flare

Abstract

We present analysis of a pair of unusually energetic coronal hard X-ray (HXR) sources detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the impulsive phase of an X3.9 class solar flare on 2003 November 3, which simultaneously shows two intense footpoint (FP) sources. A distinct loop top (LT) coronal source is detected up to ∼150 keV and a second (upper) coronal source up to ∼80 keV. These photon energies, which were not fully investigated in earlier analysis of this flare, are much higher than commonly observed in coronal sources and pose grave modeling challenges. The LT source in general appears higher in altitude with increasing energy and exhibits a more limited motion compared to the expansion of the thermal loop. The high energy LT source shows an impulsive time profile and its nonthermal power law spectrum exhibits soft-hard-soft evolution during the impulsive phase, similar to the FP sources. The upper coronal source exhibits an opposite spatial gradient and a similar spectral slope compared to the LT source. These properties are consistent with the model of stochastic acceleration of electrons by plasma waves or turbulence. However, the LT and FP spectral index difference (varying from ∼0-1) is much smaller than commonly measured and than that expected from a simple stochastic acceleration model. Additional confinement or trapping mechanisms of high energy electrons in the corona are required. Comprehensive modeling including both kinetic effects and the macroscopic flare structure may shed light on this behavior. These results highlight the importance of imaging spectroscopic observations of the LT and FP sources up to high energies in understanding electron acceleration in solar flares. Finally, we show that the electrons producing the upper coronal HXR source may very likely be responsible for the type III radio bursts at the decimetric/metric wavelength observed during the impulsive phase of this flare.

Hard X-ray emitting energetic electrons and photospheric electric currents

“…Its location is also very close to the position of the maximum of the elongated X-ray source in the 40−60 keV range. This highenergy source could be similar to coronal sources more easily observed in the case of limb events (Krucker et al 2008(Krucker et al , 2010Chen & Petrosian 2012;Su et al 2013), but projected on the disk in our case. The combined location of coronal and looptop sources could trace the location where the main reconnection process occurs, i.e.…”

Radio evidence for breakout reconnection in solar eruptive events

“…2c). Notice that this feature is not at all a type III burst as assumed by Chen & Petrosian (2012). Several positively drifting features resemble the herringbone type II burst fine structure.…”

“…9.). This phenomenon is known from other events (Sui et al 2004;Liu et al 2009;Holman et al 2011), but is not yet fully understood (see also Chen & Petrosian 2012).…”

“…The flare occurred in NOAA AR10488 in the northern hemisphere, and near the west limb (at N07W72). It was the subject of a sequence of earlier papers (Dauphin et al 2005;Vršnak et al 2005Vršnak et al , 2006Dauphin et al 2006;Veronig et al 2006;Chen & Petrosian 2012). Here we consider the impulsive phase of the event, concentrating on key details of high time resolution complementary radio data.…”

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

“…Karlický, 2009;Simões and Kontar, 2013), in particular in the above-the-looptop source (e.g. Krucker et al, 2010;Ishikawa et al, 2011;Chen and Petrosian, 2012;Oka et al, 2013Oka et al, , 2015Krucker and Battaglia, 2014). This clearly indicates that time-dependent and non-equilibrium processes exist in the solar corona during flares.…”