  During 2003 and 2004 the Anomalous X-Ray Pulsar XTE J1810-197 went through a
series of four bursts. The spectrum in the tail of one of these bursts shows a
strong, significant emission feature ~13 keV, thereby encoding a wealth of
information about the environment surrounding this object. In this paper we
analyse this emission feature considering both cyclotron and atomic emission
processes and weigh our findings against three leading AXP models: the Magnetar
model, Fall-back disk model and the Quark nova model. We find that atomic
emission from Rubidium within a Keplerian ring ($\sim$15 km from a compact
object of $\sim 2M_\odot$) is the most consistent scenario with the
observations, supporting the Quark nova model. Cyclotron emission from an
atmosphere a few hundred meters thick also fits the feature well, but is ruled
out on account of its positional coincidence in three separate AXP sources.

High Energy Astrophysical Phenomena