magnetospheric activities. In this paper we explore a more complex internal field configuration, adding a large crustal toroidal field aligned about the magnetic dipole axis to suppress heat conduction everywhere except toward the magnetic poles of the NS. While the idea of using crustal field to suppress heat conduction is not new (e.g., Geppert et al. 2004, 2006), our goal is to use the observed X-ray light curve to quantitatively constrain the magnitude and shape of this hidden toroidal field.

To quantitatively model the X-ray light curve of a magnetic NS, it is necessary to add up emissions from all surface patches of the star, taking account of beaming/anisotropy due to magnetic fields and light bending due to general relativity (Zane & Turolla 2006). While this is conceptually straightforward, it is not easy to implement in practice, as atmosphere models for many surface patches (each with different $T_{\rm eff}$ and ${\bf B}$) are needed. Therefore, in Section 2 we develop a practical method, termed “Temperature Template with Full Transport” (TTFT), for computing radiation intensity from different surface patches. This method captures the essential features of radiation from magnetic atmospheres, but does not require full self-consistent atmosphere modeling for each surface 