J. G. Coelho, M. Malheiro
The Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) are some of the most interesting groups of pulsars that have been intensively studied in the recent years. They are seen usually as neutron stars with super strong magnetic fields, namely $B\gtrsim10^{14}$ G. However, in the last two years two SGRs with low magnetic fields $B\sim(10^{12}-10^{13})$ G have been detected. Moreover, fast and very magnetic WD pulsars have also been observed in the last years. Based on these new pulsar discoveries, white dwarf pulsars have been proposed as an alternative explanation to the observational features of SGRs and AXPs. The pulsar magnetic dipole moment depending only on the momentum of inertia $I$, and the observational properties as the period $P$ and its first time derivative $\dot{P}$, can help to identify the scale of $I$ for SGRs/AXPs. We discuss here the pulsar magnetic dipole moment $m$ of SGRs and AXPs when a model based on a massive fast rotating highly magnetized white dwarf is considered. We show that the values for $m$ obtained for almost all SGRs and AXPs are in agreement with the observed range $10^{34}{\rm emu}\leq m \leq10^{36}{\rm emu}$ of isolated and polar magnetic white dwarfs, excepted for the two SGRs with low $B$ and the AE Aquarii white dwarf pulsar where $m \simeq10^{33}$ emu. This supports the understanding of SGRs and AXPs as belonging to a class of very fast and magnetic massive white dwarfs, perfect in line to the recent astronomical observations of fast white dwarf pulsars.
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http://arxiv.org/abs/1211.6078
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