Carmine Cuofano, Alessandro Drago, Giuseppe Pagliara
The Fermi LAT collaboration has recently reported the discovery of the pulsations of the $\gamma$ ray pulsar J1823-3021A with a luminosity which is the highest observed to date for any millisecond pulsar (MSP). This large luminosity implies a large spin down rate $\dot P$ and therefore a large magnetic field which seems to be incompatible with the observed short rotation period $P$. A possible explanation for the observed $P$ and $\dot P$ is to assume a very small radius for the star but it turns out that this interpretation requires rather extreme astrophysical conditions. Here we show that the data can be explained by considering the increase of the external magnetic field due to the diffusion of an internal magnetic field generated by r-modes during mass accretion. Our analysis offers a first evidence of the strong enhancement of the internal magnetic field due to the r-modes, what has been proposed in several papers. Moreover, the diffusion of the internal magnetic field provides a new evolutionary path for millisecond pulsars.
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http://arxiv.org/abs/1203.1008
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