A time-variable, phase-dependent emission line in the X-ray spectrum of the isolated neutron star RX J0822-4300

TL;DR

This study reveals a phase-dependent emission line in the X-ray spectrum of the neutron star RX J0822-4300, with evidence of its energy variation over years, suggesting dynamic magnetic or accretion processes.

Contribution

The paper provides the first detailed phase-resolved analysis of the emission line and reports its temporal variation, offering new insights into the neutron star's magnetic environment.

Findings

Confirmed the existence of a phase-dependent emission line at 0.8 keV.

Detected a decrease in the line's central energy from 2001 to 2010.

Suggested possible origins of the line include cyclotron scattering or low-rate accretion.

Abstract

RX J0822-4300 is the Central Compact Object associated with the Puppis A supernova remnant. Previous X-ray observations suggested RX J0822-4300 to be a young neutron star with a weak dipole field and a peculiar surface temperature distribution dominated by two antipodal spots with different temperatures and sizes. An emission line at 0.8 keV was also detected. We performed a very deep (130 ks) observation with XMM-Newton, which allowed us to study in detail the phase-resolved properties of RX J0822-4300. Our new data confirm the existence of a narrow spectral feature, best modelled as an emission line, only seen in the `Soft' phase interval - when the cooler region is best aligned to the line of sight. Surprisingly, comparison of our recent observations to the older ones yields evidence for a variation in the emission line component, which can be modelled as a decrease in the central energy from ~0.80 keV in 2001 to ~0.73 keV in 2009--2010. The line could be generated via cyclotron scattering of thermal photons in an optically thin layer of gas, or - alternatively - it could originate in low-rate accretion by a debris disk. In any case, a variation in energy, pointing to a variation of the magnetic field in the line emitting region, cannot be easily accounted for.