Abstract
Abstract. We study fast sausage waves in a model coronal loop that consists of a cylindrical core with axial magnetic field and coaxial annulus with purely azimuthal magnetic field. The magnetic field is discontinuous at the tube and core boundaries, and there are surface currents with the opposite directions on these boundaries. The principal mode of fast sausage waves in which the magnetic pressure perturbation has no nodes in the radial direction can exist for arbitrary wavelength. The results for the fundamental radial mode of sausage waves are applied to the interpretation of observed periodic pulsations of microwave emission in flaring loops with periods of a few tens of seconds. Radial plasma motion has opposite directions at the tube and core boundaries. This leads to the periodic contraction and expansion of the annulus. We assume that the principal mode of fast sausage waves in the current-carrying coronal loops is able to produce a current sheet. However, the nonlinear analysis is needed to confirm this conjecture.
Highlights
It is commonly accepted that a source of energy of simpleloop flares is electric currents that flow from one loop footpoint to the other (Alfvén and Carlqvist, 1967)
The first one is the coronal loops can be currentneutral, and the current integrated over the loop cross section is zero
Bembitov et al.: Structure of fast sausage waves in coronal loops case of smooth inhomogeneity of the plasma density in the radial direction, the period of a sausage oscillation always increases with the increase of the longitudinal wavelength, and this dependence saturates in the long-wavelength limit (Nakariakov et al, 2012)
Summary
It is commonly accepted that a source of energy of simpleloop flares is electric currents that flow from one loop footpoint to the other (Alfvén and Carlqvist, 1967). Fast sausage modes of flaring coronal loops can effectively modulate their microwave and hard X-ray emission by varying a “loss cone” for accelerated electrons (Zaitsev–Stepanov mechanism) These oscillations are observed as quasi-periodic pulsations with periods from subseconds to a few minutes (Zaitsev and Stepanov, 1983; Aschwanden, 1987; Inglis et al, 2008; Nakariakov and Melnikov, 2009). Bembitov et al.: Structure of fast sausage waves in coronal loops case of smooth inhomogeneity of the plasma density in the radial direction, the period of a sausage oscillation always increases with the increase of the longitudinal wavelength, and this dependence saturates in the long-wavelength limit (Nakariakov et al, 2012).
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