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We study the intensity, the modulation depth and the mean modulation depth ofthe gyrosynchrotron (GS) radiation as a function of the frequency and the lineof sight (LOS) in fast sausage modes. By solving the 2.5D MHD ideal equationsof a straight coronal loop considering the chromosphere and with typicalflaring plasma parameters we analyse the wavelet transform of the density andthe GS emission for different radio frequencies and different spatialresolutions, given impulsive and general perturbations with energies in themicroflare range. A wavelet analysis performed over the GS radiation emissionshowed that a fast fundamental sausage mode of 7s with a first harmonic mode of3s developed, for all the initial energy perturbations used. For both the highspatial resolution (central pixel integration) and the low spatial resolution(entire loop integration), the larger the radio frequency, the larger themodulation depth. However, high and low resolution integrations differ in that,the larger the LOS angle with respect to the loop axis, results in a larger andsmaller modulation depth, respectively. Fast MHD modes triggered byinstantaneous energy depositions of the order of a microflare energy are ableto reproduce deep intensity modulation depths in radio emission as observed insolar events. As the trends of the GS emission obtained by Reznikova, Antolin,and Van Doorsselaere (2014), for a linear and forced oscillation, remainpresent when analysing a more general context, considering the chromosphere andwhere the sausage mode is triggered by a impulsive, nonlinear perturbation, itseems that the behaviour found can be used as observational identifiers of thepresence of sausage modes with respect to other quasi-periodic pulsationfeatures. It can be inferred from this that finite-amplitude sausage modes havethe potential to generate the observed deep modulation depths.

Modulation depth of the gyrosynchrotron emission as identifier of fundamental sausage modes