Discovery of X-Rays from the Old and Faint Pulsar J1154-6250

Abstract

We report on the first X-ray observation of the 0.28 s isolated radio pulsar PSR J1154-6250 obtained with the XMM-Newton observatory in 2018 February. A point-like source is firmly detected at a position consistent with that of PSR J1154-6250. The two closest stars are outside the 3σ confidence limits of the source position and thus unlikely to be responsible for the observed X-ray emission. The energy spectrum of the source can be fitted equally well either with an absorbed power law with a steep photon index Γ ≈ 3.3 or with an absorbed blackbody with temperature kT = 0.21 ± 0.04 keV and emitting radius R <SUB>BB</SUB> ≈ 80 m (assuming a distance of 1.36 kpc). The X-ray luminosity of 4.4 × 10<SUP>30</SUP> erg s<SUP>-1</SUP> derived with the power-law fit corresponds to an efficiency of {η }<SUB>X</SUB>={L}<SUB>X</SUB><SUP>unabs</SUP>}/\dot{E}=4.5× {10}<SUP>-3</SUP>, similar to those of other old pulsars. The X-ray properties of PSR J1154-6250 are consistent with an old age and suggest that the spatial coincidence of this pulsar with the OB association Cru OB1 is due to a chance alignment.