The continued spectral and temporal evolution of RX J0720.4−3125

• Published in: Monthly notices of the Royal Astronomical Society Vol. 423; no. 2; pp. 1194 - 1199
• Main Authors: Hohle, M. M., Haberl, F., Vink, J., de Vries, C. P., Turolla, R., Zane, S., Méndez, M.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.06.2012
• Subjects: pulsars: individual: RX J0720.4−3125; stars: neutron; stars: neutron; pulsars: individual: RX J0720.4−3125
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2012.20946.x

RX J0720.4−3125 is the most peculiar object among a group of seven isolated X-ray pulsars (the so-called Magnificent Seven), since it shows long-term variations of its spectral and temporal properties on time-scales of years. This behaviour was explained by different authors either by free precession (with a 7 or 14 yr period) or possibly a glitch that occurred around MJD = 528 66 ± 73 d. We analysed our most recent XMM-Newton and Chandra observations in order to further monitor the behaviour of this neutron star. With the new data sets, the timing behaviour of RX J0720.4−3125 suggests a single (sudden) event (e.g. a glitch) rather than a cyclic pattern as expected by free precession. The spectral parameters changed significantly around the proposed glitch time, but more gradual variations occurred already before the (putative) event. Since MJD ≈ 530 00 d the spectra indicate a very slow cooling by ∼2 eV over 7 yr.