Discovery of X-rays from the old and faint pulsar J1154--6250

TL;DR

This paper reports the first detection of X-ray emission from the old pulsar PSR J1154--6250 using XMM-Newton, revealing spectral properties consistent with typical old pulsars and providing insights into its age and emission efficiency.

Contribution

First X-ray observation of PSR J1154--6250, characterizing its spectral properties and emission efficiency, and clarifying its association with the Cru OB1 region.

Findings

X-ray emission detected at the pulsar's position.

Spectral fit with power-law or blackbody models.

X-ray efficiency similar to other old pulsars.

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 February 2018. A point-like source is firmly detected at a position consistent with that of PSR J1154--6250. The two closest stars are outside the 3$\sigma$ 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 $\Gamma\approx 3.3$ or with an absorbed blackbody with temperature $kT=0.21\pm 0.04$~keV and emitting radius $R_\mathrm{BB} \approx 80$ m (assuming a distance of 1.36~kpc). The X-ray luminosity of $4.4\times 10^{30}$ erg s$^{-1}$ derived with the power-law fit corresponds to an efficiency of $\eta_X = L^\mathrm{unabs}_X/\dot E = 4.5\times 10^{-3}$, 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.