Very deep X-ray observations of the anomalous X-ray pulsar 4U 0142+614

Abstract

We report on two new XMM-Newton observations of the anomalous X-ray pulsar (AXP) 4U 0142+614 performed in 2004 March and July, collecting the most accurate spectrum for this source. Furthermore, we analyse two short archival observations performed in 2002 February and 2003 January in order to study the long-term behaviour of this AXP. 4U 0142+614 appears to be relatively steady in flux between 2002 and 2004, and the phase-averaged spectrum does not show any significant variability between the four epochs. We derive the deepest upper limits to date on the presence of lines in 4U 0142+614 spectrum as a function of energy: equivalent width in the 1-3 keV energy range <4 and <8 eV for narrow and broad lines, respectively. A remarkable energy dependence in both the pulse profile and the pulsed fraction is detected, and consequently pulse-phase spectroscopy shows spectral variability as a function of phase. By making use of XMM-Newton and INTEGRAL data, we successfully model the 1-250 keV spectrum of 4U 0142+614 with three models, namely the canonical absorbed blackbody plus two power laws, a resonant cyclotron scattering model plus one power-law and two log-parabolic functions. © 2007 RAS.