X-ray nondetection of PSR J0250+5854

TL;DR

This study used deep X-ray observations to set upper limits on the X-ray luminosity of the long-period pulsar PSR J0250+5854, exploring its connection to other neutron star classes and constraining its thermal properties.

Contribution

It provides the first deep X-ray upper limit for PSR J0250+5854, comparing it with XDINSs and magnetars to understand its nature and thermal characteristics.

Findings

X-ray emission was not detected, with an upper luminosity limit of <10^31 erg/s.

The upper limit is below the luminosity of all but one XDINS.

If PSR J0250+5854 has a hot spot, its temperature is constrained to <200 eV.

Abstract

We conducted a deep XMM$\unicode{x2013}$Newton observing campaign on the 23.5-s radio pulsar PSR J0250+5854 in order to better understand the connection between long-period, radio-emitting neutron stars and their high-energy-emitting counterparts. No X-ray emission was detected resulting in an upper limit in the bolometric luminosity of PSR J0250+5854 of $<$10$^{31}$ erg s$^{-1}$ for an assumed blackbody with a temperature of 85 eV, typical of an X-ray Dim Isolated Neutron Star (XDINS). We compared the upper limit in the bolometric luminosity of PSR J0250+5854 with the known population of XDINSs and found that the upper limit is lower than the bolometric luminosity of all but one XDINS. We also compared PSR J0250+5854 with SGR 0418+5729, the magnetar with low dipole magnetic field strength, where the upper limit suggests that if PSR J0250+5854 has a thermal hot spot like SGR 0418+5729, it would have a blackbody temperature of $<$200 eV, compared to 320 eV of the magnetar.