Influence of Fine Structures on Gyrosynchrotron Emission of Flare Loops Modulated by Sausage Modes

Abstract

Sausage modes are a leading mechanism for interpreting short-period quasi-periodic pulsations (QPPs) of solar flares. Forward modeling their radio emission is crucial for identifying sausage modes observationally and for understanding their connections with QPPs. Using the numerical outputs from three-dimensional magnetohydrodynamic simulations, we forward model the gyrosynchrotron emission of flare loops modulated by sausage modes and examine the influence of fine structures of loops. The temporal evolution of the emission intensity is analyzed for an oblique line of sight crossing the loop center. We find that the low- and high-frequency intensities oscillate in phase in the periods of sausage modes for models with or without fine structures. For low-frequency emissions where the optically thick regime arises, the modulation magnitude of the intensity is dramatically reduced by the fine structures at some viewing angles. On the contrary, for high-frequency emissions where the optically thin regime holds, the effects of fine structures or the viewing angle are marginal. Our results show that the periodic intensity variations of sausage modes are not wiped out by fine structures, and that sausage modes remain a promising candidate mechanism for QPPs, even when the flare loops are fine-structured.