The extended X-ray emission around RRAT J1819-1458

We present new imaging and spectral analysis of the recently discovered extended X-ray emission around the high magnetic field rotating radio transient RRAT J1819-1458. We used two Chandra observations performed for this object in 2008 May 31 and 2011 May 28, respectively. The diffuse X-ray emission was detected with a significance of \sim19 sigma in the image obtained by combining the two observations. Neither long-term spectral nor timing variability have been observed from the source or the nebula. RRAT J1819-1458 shows an unusual high X-ray efficiency of L_x(0.3-5 keV)/Edot_{rot} \sim 0.15 at converting spin-down power into X-ray luminosity. The most favourable scenario for the origin of this extended X-ray emission is either a pulsar-wind nebula (PWN) or a scattering halo. A magnetically powered scenario for the extended emission is viable only in the case of a Compton nebula, while can be tentatively disfavoured in the case of synchrotron emission.