The X-ray properties of the energetic pulsar PSR J1838-0655

We present and interpret several new X-ray features of the X-ray pulsar PSR J1838-0655. The X-ray data are obtained from the archival data of Chandra, RXTE and Suzaku. We combine all these X-ray data and fit the spectra with different models. We find that the joint spectra are difficult to fit with a single power law; a broken power-law model with a break at around 6.5 keV can improve the fit significantly. The photon index changes from Γ = 1.0 (below 6.5 keV) to 1.5 (above 6.5 keV); this indicates a softer spectral behaviour at hard X-rays. The X-ray flux at 2-20 keV is found to be 1.6 × 10^-11 erg cm^-2 s^-1. The conversion efficiency from the spin-down luminosity is ∼0.9 per cent at 0.8-10 keV, which is much higher than that (∼10^-3 to 10^-4 per cent) of the pulsars that show similar timing properties. We discuss non-thermal radiation mechanisms for the observed high X-ray conversion efficiency and find that emission from the magnetosphere of a greatly inclined rotator is the most favourable interpretation for the conversion rate and the pulse profiles at X-ray bands. A line feature close to 6.65 keV is also detected in the spectra of Suzaku/X-ray imaging spectrometer; it might be the Kα emission of highly ionized Fe surrounding the pulsar.