Magnetic structure of solar flare regions producing hard X-ray pulsations

Abstract

located at the footpoints of different magnetic field lines wrapping around the central axis, and constituting an MFR by themselves. In five other flares the parent field lines of the HXR pulsations were not a part of an MFR, but surrounded it in the form of an arcade of magnetic loops. These results show that, at least in the analyzed cases, the "single flare loop" models do not satisfy the observations and magnetic field modeling, while are consistent with the concept that the HXR pulsations are a consequence of successive episodes of energy release and electron acceleration in different magnetic flux tubes (loops) of a complex AR. An MFR could generate HXR pulsations by triggering episodes of magnetic reconnection in different loops in the course of its non-uniform evolution along an MPIL. However, since three events studied here were confined flares, actual eruptions may not be required to trigger sequential particle acceleration episodes in the magnetic systems containing an MFR.

Roles of Photospheric Motions and Flux Emergence in the Major Solar Eruption on 2017 September 6

“…It is worth noting that the X-ray sources are spread to the south along the magnetic PIL (RHESSI contours in Figure 2b) when the flare develops near its peak time. The position of the reconnection signatures changes probably due to involvement of different magnetic field lines into the energy release process (e.g., Priest & Longcope 2017;Zimovets et al 2018). The brightening in Figure 2a may correspond to the initial reconnection by footpoint motions, and the one in Figure 2b may be related to the reconnection beneath the rising plasmoid.…”

Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures

“…Their development was motivated by the presence of sequential bursts of non-thermal radiation in the impulsive phase of many flares (often in the form of QPPs) and by signs of sequential ignition of flare loops in magnetic arcades lined up along the magnetic polarity inversion line (PIL). These features include sequential brightening of arcade loops in the soft X-ray or EUV ranges (Vorpahl, 1976;Reva et al, 2015), expansion of flare ribbons along the PIL (Qiu et al, 2010), and the apparent movement of flare non-thermal hard X-ray Grigis and Benz, 2005;Zimovets and Struminsky, 2009;Kuznetsov et al, 2016;Zimovets et al, 2018) and microwave (Kuznetsov et al, 2017) sources along the PIL (see an example in Figure 20).…”

Relationships between Photospheric Vertical Electric Currents and Hard X-Ray Sources in Solar Flares: Statistical Study

“…The impulsive phase of many solar flares is a sequence of HXR peaks of duration from a fraction of second to several tens of seconds (Dennis 1988;Aschwanden 2002). Moreover, it is known that the sources of individual HXR peaks can be located in different places, usually in footpoints of different flux tubes organized in magnetic arcades and/or more complex structures, like magnetic flux ropes (e.g., Fletcher & Hudson 2002;Krucker et al 2003;Kuznetsov et al 2016;Zimovets et al 2018).…”