De Luca, A; Salvetti, D; Sartori, A; Esposito, P; Tiengo, A; Zane, S; Turolla, R; ... Bignami, GF; + view all De Luca, A; Salvetti, D; Sartori, A; Esposito, P; Tiengo, A; Zane, S; Turolla, R; Pizzolato, F; Mignani, RP; Caraveo, P; Mereghetti, S; Bignami, GF; - view fewer (2012) A time-variable, phase-dependent emission line in the X-ray spectrum of the isolated neutron star RX J0822-4300. Monthly Notices of the Royal Astronomical Society: Letters , 421, (1) L72 - L76. 10.1111/j.1745-3933.2011.01209.x.

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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 2009-10. 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 disc. 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.

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