X-RAY AND EUV OBSERVATIONS OF SIMULTANEOUS SHORT AND LONG PERIOD OSCILLATIONS IN HOT CORONAL ARCADE LOOPS

Abstract

We report decaying quasi-periodic intensity oscillations in the X-ray (6-12\nkeV) and extreme ultraviolet (EUV) channels (131, 94, 1600, 304 \\AA) observed\nby the Fermi GBM (Gamma-ray Burst Monitor) and SDO/AIA, respectively, during a\nC-class flare. The estimated period of oscillation and decay time in the X-ray\nchannel (6-12 keV) was about 202 s and 154 s, respectively. A similar\noscillation period was detected at the footpoint of the arcade loops in the AIA\n1600 and 304 \\AA channels. Simultaneously, AIA hot channels (94 and 131 \\AA)\nreveal propagating EUV disturbances bouncing back and forth between the\nfootpoints of the arcade loops. The period of the oscillation and decay time\nwere about 409 s and 1121 s, respectively. The characteristic phase speed of\nthe wave is about 560 km/s for about 115 Mm loop length, which is roughly\nconsistent with the sound speed at the temperature about 10-16 MK (480-608\nkm/s). These EUV oscillations are consistent with the SOHO/SUMER Doppler-shift\noscillations interpreted as the global standing slow magnetoacoustic wave\nexcited by a flare. The flare occurred at one of the footpoints of the arcade\nloops, where the magnetic topology was a 3D fan-spine with a null-point.\nRepetitive reconnection at this footpoint could cause the periodic acceleration\nof non-thermal electrons that propagated to the opposite footpoint along the\narcade and precipitating there, causing the observed 202-s periodicity. Other\npossible interpretations, e.g. the second harmonics of the slow mode are also\ndiscussed.\n