Are Flare Quasi-periodic Pulsations Signatures of Intermittent Reconnection?
Abstract
Flare quasi-periodic pulsations (QPPs) have been observed over a vast energy spectrum, from radio to hard x-rays. The periodicities of these fine structures range from tens of milliseconds to tens of seconds and suggest highly structured but intermittent energy release. In some cases, the sources of microwaves and thermal hard x-rays are situated near the apex of the flare loop arcades and are not stationary. Although it is unclear whether all the observed varieties of QPPs can be explained via a single, unified process, our recent high-resolution simulations of a breakout eruptive flare (Karpen et al. 2012) indicate that spatially and temporally localized reconnection is a plausible candidate for these bursts of radiation. With our null-tracking capabilities, we follow the creation and evolution of X- and O-type nulls in the flare current sheet and characterize their periodicity. QPPs located at the apex of the flare arcade may result from the interaction of downward-moving islands in the sheet with the arcade below. Each island is composed of highly twisted magnetic field lines that comprise a single reconnected flux tube. Upon arrival at the top of the flare loops, secondary reconnection events between the island and the arcade produce discrete energy release events that could be related to observed QPPs in that region. Different regimes of current-sheet reconnection (slow/fast), island sizes, rates of island coalescence, and rates of reconnection between islands and arcades may all help to explain the variety of energy and time scales exhibited by the flare QPPs.Abstract (2,250 Maximum Characters): Flare quasi-periodic pulsations (QPPs) have been observed over a vast energy spectrum, from radio to hard x-rays. The periodicities of these fine structures range from tens of milliseconds to tens of seconds and suggest highly structured but intermittent energy release. In some cases, the sources of microwaves and thermal hard x-rays are situated near the apex of the flare loop arcades and are not stationary. Although it is unclear whether all the observed varieties of QPPs can be explained via a single, unified process, our recent high-resolution simulations of a breakout eruptive flare (Karpen et al. 2012) indicate that spatially and temporally localized reconnection is a plausible candidate for these bursts of radiation. With our null-tracking capabilities, we follow the creation and evolution of X- and O-type nulls in the flare current sheet and characterize their periodicity. QPPs located at the apex of the flare arcade may result from the interaction of downward-moving islands in the sheet with the arcade below. Each island is composed of highly twisted magnetic field lines that comprise a single reconnected flux tube. Upon arrival at the top of the flare loops, secondary reconnection events between the island and the arcade produce discrete energy release events that could be related to observed QPPs in that region. Different regimes of current-sheet reconnection (slow/fast), island sizes, rates of island coalescence, and rates of reconnection between islands and arcades may all help to explain the variety of energy and time scales exhibited by the flare QPPs.
- Publication:
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AAS/Solar Physics Division Abstracts #44
- Pub Date:
- July 2013
- Bibcode:
- 2013SPD....44...85G