On the Zebra Structure in the Frequency Range near 3 GHz

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Abstract
We present 19 cases of zebra pattern structure (ZPS) and fiber bursts (FB) in radio bursts in frequency range around 3GHz, and one such case in the range 5.2-7.6GHz, using the new microwave spectrometer of NAOC between 2.6- 3.8 and 5.2-7.6GHz (China, Huairou station) with high resolution (10MHz and 8ms). The FB and ZPS have about the same spectral parameters: the frequency bandwidth of emission stripes f 20MHz, the frequency separation between the emission and the neighboring low frequency absorption fea 30MHz and the frequency separation between emission stripes (when a periodic structure persists) fs 60-70MHz. Therefore we consider both these fine structures to be whistler manifestations, i.e., interactions of plasma electrostatic waves with whistler waves (generated by the same fast particles with loss-cone anisotropy) l + w ! t. The duration of the fiber bursts of about 2s corresponds to whistler waves propagat- ing undamped at about 2s, which requires a whistler increment < 0.5 s 1. In the frequency range 3-7GHz the relation between the ratios of plasma to cyclotron frequencies and whistler to cyclotron frequencies is almost independent of the decre- ment of whistler electron damping. This finding is used to obtain the magnetic field strength in the region of generation. For a reasonable value of electron temperature (2-20MK), we find B = 125 190G when the electron density is (8 18)◊1010 cm 3 and B = 520 610G when the electron density is (35-60)◊1010 cm 3. In two re- markable events, 1998-04-15 and 2000-10-29, the right-hand polarization is strong for all the fine structures and corresponds to ordinary wave.

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