Kavli Affiliate: Renxin Xu
| First 5 Authors: Guojun Qiao, Lunhua Shang, Renxin Xu, Kejia Lee, Yongquan Xue
| Summary:
The emission of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Ray Repeaters
(SGRs) is believed to be powered by the dissipation of their strong magnetic
fields, which coined the name `magnetar’. By combining timing and energy
observational results, the magnetar model can be easily appreciated. From a
timing perspective, the magnetic field strengths of AXPs and SGRs, calculated
assuming dipole radiation, are extremely strong. From an energy perspective,
the X-ray/soft gamma-ray luminosities of AXPs and SGRs are larger than their
rotational energy loss rates (i.e., $ L_{rm X}>dot E_{rm rot}$). It is thus
reasonable to assume that the high-energy radiation comes from magnetic energy
decay, and the magnetar model has been extensively discussed (or accepted).
However, we argue that: (1) calculating magnetic fields by assuming that
rotational energy loss is dominated by dipole radiation (i.e., $dot{E}_{rm
rot}simeqdot{E}_{mu}$)) may be controversial, and we suggest that the
energies carried by outflowing particles should also be considered; and (2) the
fact that X-ray luminosity is greater than the rotational energy loss rate does
not necessarily mean that the emission energy comes from the magnetic field
decaying, which requires further observational testing. Furthermore, some
observational facts conflict with the `magnetar’ model, such as observations of
anti-magnetars, high magnetic field pulsars, and radio and X-ray observations
of AXPs/SGRs. Therefore, we propose a crusted strange star model as an
alternative, which can explain many more observational facts of AXPs/SGRs.
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