GB1 - Fast radio bursts: observations, ideas and prospects |
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Speaker |
Yang, Yuanpei |
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Coauthors |
Yang, Yuanpei; Zhang, Bing |
| Talk Title |
Coherent Curvature Radiation by Bunches: Application to Fast Radio Bursts |
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Abstract |
The extremely high brightness temperatures of fast radio bursts (FRBs) require their radiation mechanisms to be coherent. We develop a general radiation theory of coherent curvature radiation by bunches under a three-dimensional magnetic field geometry from the first principles. We consider a bunch characterized by its length, curvature radius of the trajectory family, bunch opening angle, and electron energy distribution, and find that the curvature radiation spectra of these bunches are characterized by a multi-segment broken power law, with the break frequencies depending on bunch properties and trajectory configuration. We emphasize that in a pulsar magnetosphere only the fluctuation of net charges with respect to the Goldreich-Julian outflow can make a contribution to coherent radiation. We apply this model to constrain the observed spectra of pulsars and FRBs. For a typical pulsar ($B_p=10^{12}~\unit{G}$, $P=0.1~\unit{s}$), a small fluctuation of the net charge $\delta n_{\rm GJ}\sim 0.1 n_{\rm GJ}$ can provide the observable flux. For FRBs, the fluctuating net charge may be larger due to its abrupt nature. For $\delta n_{\rm GJ}\sim n_{\rm GJ}$, a neutron star with a strong magnetic field and fast rotation is required to power an FRB in the spindown-powered model. The requirement is less stringent in the cosmic comb model thanks to the larger cross section and compressed charge density of the bunch made by the external astrophysical stream that combs the magnetosphere. |
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