MG13 - Talk detail

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In recent years the compact objects known as Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) have been intensively studied, and understood as neutron star pulsars with super strong magnetic fields. Transient AXPs, 5 over a total of about 20 SGRs/AXPs, show several properties that make them different: loud radio (transient radio emission different of the radio pulsar emission), low quiescent X-ray luminosity $L_X$ (decreasing fast with time) that can be explained from the spin-down rotational energy lost $\dot{E}$ of a neutron star, as normal rotation-powered pulsar. We present here the X-ray pulsar efficiency $\eta_X=L_X/\dot{E}$ for these transient AXPs, and show that $\eta_X\sim(0.2-0.1)$ larger than for normal pulsars (where $\eta_X\sim(0.3-0.4)$), due to their big magnetic dipole momentum $m\sim10^{32}$ emu, giving support for their NS interpretation. A comparison between transient AXPs and XDINS is also present here. The large steady X-ray luminosity (and almost constant) seen for the others SGRs/AXPs also can be explained as coming from a large spin-down energy lost of a massive white dwarf, and also from a much large magnetic dipole moment of $10^{34}\leq m\leq10^{36}$ emu consistent with the range observed for isolated and very magnetic WDs, indicating a different nature between these sources and the transient AXPs.

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