%0 Journal Article
%A De Luca, A
%A Salvetti, D
%A Sartori, A
%A Esposito, P
%A Tiengo, A
%A Zane, S
%A Turolla, R
%A Pizzolato, F
%A Mignani, RP
%A Caraveo, P
%A Mereghetti, S
%A Bignami, GF
%D 2012
%F discovery:1386976
%I WILEY
%J Monthly Notices of the Royal Astronomical Society: Letters
%N 1
%P L72 - L76
%T A time-variable, phase-dependent emission line in the X-ray spectrum of the isolated neutron star RX J0822-4300
%U https://discovery.ucl.ac.uk/id/eprint/1386976/
%V 421,
%X 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.
%Z © 2012 RAS