We present systematic analysis of the spatio-temporal evolution of sources of hard X-ray (HXR) pulsations in solar flares. We concentrate on disk flares whose impulsive phase are accompanied by a series of more than three successive peaks (pulsations) of HXR emission detected in the RHESSI 50-100 keV energy channel with 4-second time cadence. 29 such flares observed from February 2002 to June 2015 with characteristic time differences between successive peaks P ≈ 8 − 270 s are studied. The main observational result of the analysis is that sources of HXR pulsations in all flares are not stationary, they demonstrate apparent movements/displacements in parental active regions from pulsation to pulsation. The flares can be subdivided into two main groups depending on the character of dynamics of HXR sources. The group-1 consists of 16 flares (55%) with the systematic dynamics of the HXR sources from pulsation to pulsation with respect to a magnetic polarity inversion line (MPIL), which has simple extended trace on the photosphere. The group-2 consists of 13 flares (45%) I.V. Zimovets ivanzim@iki.rssi.ru with more chaotic displacements of the HXR sources with respect to an MPIL having more complicated structure, and sometimes several MPILs are presented in parental active regions of such flares. Based on the observations we conclude that the mechanism of the flare HXR pulsations (at least with time differences of the considered range) is related to successive triggering of flare energy release process in different magnetic loops (or bundles of loops) of parental active regions. Group-1 flare regions consist of loops stacked into magnetic arcades extended along MPILs. Group-2 flare regions have more complicated magnetic structures and loops are arranged more chaotically and randomly there. We also found that at least 14 (88%) group-1 flares and 11 (85%) group-2 flares are accompanied by coronal mass ejections (CMEs), i.e. the absolute majority of the flares studied are eruptive events. This gives a strong indication that eruptive processes play important role in generation of HXR pulsations in flares. We suggest that an erupting flux rope can act as a trigger of flare energy release. Its successive interaction with different loops of a parental active region can lead to apparent motion of HXR sources and to a series of HXR pulsations. However, the exact mechanism responsible for the generation of pulsations remains unclear and requires more detailed investigation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.