We report multi–wavelength study of a complex M–class solar eruptive flare that consists of three different sets of flare ribbons, viz. circular, parallel, and remote ribbons. Magnetic field modeling of source active region NOAA 12242 exhibits the presence of 3D null–point magnetic topology which encompasses an inner bipolar region. The event initiates with the faint signatures of the circular ribbon along with remote brightening right from the pre–flare phase which points toward the ongoing slow yet persistent null–point reconnection. We first detected flux cancellation and an associated brightening, which are likely signatures of tether-cutting reconnection that builds the flux rope near the polarity inversion line (PIL) of the inner bipolar region. In the next stage, with the onset of M8.7 flare, there is a substantial enhancement in the brightening of circular ribbon which essentially suggests an increase in the rate of ongoing null–point reconnection. Finally, the eruption of underlying flux rope triggers “standard flare reconnection” beneath it producing an abrupt rise in the intensity of the parallel ribbons as well as enhancing the rate of null–point reconnection by external forcing. We show that within the the fan dome, the region with magnetic decay index n>1.5 borders the null-point QSL. Our analysis suggests that both the torus instability and the breakout model have played role toward the triggering mechanism for the eruptive flare. This event is a nice example of the dynamical evolution of a flux rope initially confined in a null-point topology, that subsequently activates and erupts with the progression of the circular–cum– parallel ribbon flare.

中文翻译：

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圆形和平行带状复杂喷发耀斑的演化阶段和触发过程

我们报告了一个复杂的 M 级太阳爆发耀斑的多波长研究，该耀斑由三组不同的耀斑带组成，即。圆形、平行和远程色带。源活动区 NOAA 12242 的磁场建模展示了 3D 零点磁拓扑的存在，其中包含一个内部双极区。该事件以圆形丝带的微弱特征开始，伴随着从预耀斑阶段开始的远程增亮，这指向正在进行的缓慢但持续的零点重新连接。我们首先检测到通量抵消和相关的增亮，这可能是系绳切割重新连接的特征，在内部双极区的极性反转线 (PIL) 附近建立了通量绳。在下一阶段，随着 M8.7 耀斑的爆发，圆形带的亮度显着增强，这实质上表明正在进行的零点重新连接的速率增加。最后，底层磁链的喷发触发其下方的“标准耀斑重联”，导致平行带的强度突然上升，并通过外力提高零点重联率。我们表明，在风扇圆顶内，磁衰减指数 n>1.5 的区域与零点 QSL 相邻。我们的分析表明，环面不稳定性和爆发模型都对爆发耀斑的触发机制发挥了作用。这个事件是最初限制在零点拓扑中的磁通绳的动力学演化的一个很好的例子，