  It is now commonly believed that Soft gamma-ray repeaters (SGRs) and
Anomalous X-ray pulsars (AXPs) are magnetars -- neutron stars powered by their
magnetic fields. However, what differentiates these two seemingly dissimilar
objects is, at present, unknown. We present Chandra observations of RX
J052600.3-660433, the quiescent X-ray counterpart of SGR 0526-66. Restricting
to a period range around 8-s, the period noted in the afterglow of the burst of
5 March 1979, we find evidence for a similar periodicity in two epochs of data,
obtained 20 months apart, implying a period derivative of $6.6(5)e-11$ s/s
which is similar to the period derivatives of the magnetars. The spectrum is
best fitted by a combination of a black body and a power law. However, the
photon index of the power law component, $\Gamma\sim 3$ -- intermediate to
those of AXPs and SGRs. This continuum of $\Gamma$ leads us to suggest that the
underlying physical parameter which differentiates SGRs from AXPs is manifested
in the power law component. Two decades ago, SGR 0526-66 was a classical SGR
whereas now it behaves like an AXP. Thus it is possible that the same object
cycles between SGR and AXP state. We speculate that the main difference between
AXPs and SGRs is the geometry of the $B$-fields and this geometry is time
dependent. [Abstract truncated]
