Particle acceleration and flare triggering in large-scale magnetic loops joining widely spaced active regions

We provide new observations that contradict the canonical model of solar flare emission in the coronal loops of a single active region, and indicate instead particle acceleration and flare triggering in otherwise- invisible, large-scale magnetic loops joining widely separated active regions. Very Large Array (VLA) snapshot maps and NSO-Kitt Peak photospheric magnetograms indicate that bursts at 20 cm wavelength occurred in two widely separated active regions, and that 91 cm radiation originated in large-scale magnetic loops joining them. Images taken by the Yohkoh satellite showed no substantial enhanced soft X-ray emission from coronal loops joining these active regions either before or after the flare. Observations from the Owens Valley Solar Array (OVRO) confirm the VLA 20 cm results while also showing decimetric emission that is relatively narrow-band and superposed on a broader background. Comparisons of the time profiles of the radio radiation from the two active regions with simultaneous hard X-ray time profiles, observed with the Burst and Transient Source Spectrometer Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO), suggest that energetic electrons were first accelerated in one active region, and then injected into the large- scale magnetic loops at velocities ≥0.4c to trigger 20 cm burst emission in the active region at the other footpoint of these loops, while also leading to 91 cm radiation from the entire loop system. These observations provide another example of the diversified mechanisms for particle acceleration and flare triggering on the Sun.