  We report on the discovery of extended X-ray emission around the high
magnetic field Rotating Radio Transient J1819-1458. Using a 30ks Chandra ACIS-S
observation, we found significant evidence for extended X-ray emission with a
peculiar shape: a compact region out to 5.5", and more diffuse emission
extending out to ~13" from the source. The most plausible interpretation is a
nebula somehow powered by the pulsar, although the small number of counts
prevents a conclusive answer on the nature of this emission. RRAT J1819-1458's
spin-down energy loss rate (Edot~3x10^{32} erg/s) is much lower than that of
other pulsars with observed spin-down powered pulsar wind nebulae (PWNe), and
implies a rather high X-ray efficiency of eta_{X} = L_(pwn; 0.5-8keV)/Edot~0.2
at converting spin-down power into the PWN X-ray emission. This suggests the
need of an additional source of energy rather than the spin-down power alone,
such as the high magnetic energy of this source. Furthermore, this Chandra
observation allowed us to refine the positional accuracy of RRAT J1819-1458 to
a radius of ~0.3", and confirms the presence of X-ray pulsations and the ~1keV
absorption line, previously observed in the X-ray emission of this source.
