Speaker
Description
First Name: Sanjiv
Last Name: Tiwari
Affiliation: Lockheed Martin Solar and Astrophysics Laboratory & Bay Area Environmental Research Institute
All Authors: Navdeep Panesar, Ron Moore, Sabrina Savage, Amy Winebarger, Genevieve Vigil, Juraj Lörinčík, Vanessa Polito, Bart De Pontieu, Leon Golub, Ken Kobayashi, Patrick Champey, Jenna Samra, Ann Rankin, Robert Walsh, Crisel Suarez, Christopher Moore, Adam Kobelski, Jeffery Reep, Charles Kankelborg
Abstract: The third successful Hi-C sounding rocket flight, {\it Hi-C Flare}, recorded coronal images in Fe XXI 129 \AA\ emission from 11 MK plasma on April 17, 2024, during the post-maximum phase of an M1.6-class solar flare, achieving unprecedented spatial \textbf{( \sim$300 km)} and temporal (1.3 s) resolutions. The flare started at 21:55UT, peaked at 22:08UT, and lasted $\sim$40 minutes. Hi-C observed for over five minutes (22:15:45 to 22:21:25), starting roughly eight minutes after flare maximum. A sudden compact bright burst---875$\pm$25 km wide and lasting 90$\pm$1.3 s, splitting into two toward the end---occurs near the foot of some post-flare loops. Its size and brightness are reminiscent of flare-ribbon kernels during a flare’s rapid rise phase, kernels marking sites of sudden heating and hot plasma upflow, making its occurrence during the late phase surprising. Such isolated brightenings in a flare's post-maximum phase are rare, and have not been previously reported. The kernel was detected in all SDO/AIA channels. Its 1600 \AA\ light curve peaked $\sim$50 s earlier than its 131 \AA\ light curve, similar to that of flare-ribbon kernels, albeit with a smaller delay of $\sim$25 s, during the impulsive phase of the flare. In SDO/HMI magnetograms, the kernel sits in unipolar positive magnetic flux near an embedded clump of negative flux. While localized magnetic reconnection within the kernel (a microflare) remains a possibility, the observations suggest that the brightening represents an isolated, unusually late flare-ribbon kernel, triggered by a delayed phase of the flare’s coronal reconnection.