XMM-Newton observation of the anomalous X-ray pulsar 4U 0142+61

We present results of an observation of the anomalous X-ray pulsar 4U 0142+61 with the EPIC cameras on XMM-Newton performed on 2003 January 24. The pulse phase averaged spectrum can be best described by the sum of a black body with a temperature of kT_BB = 0.395(5) keV and a power law with photon index Γ=3.62(5). The unabsorbed 2-10 keV flux is ∼7.2× 10^-11~erg s^-1 cm^-2. No evidence for additional spectral features such as cyclotron lines is present. These results are consistent with those from an earlier Chandra observation in 2001 May. Phase resolved spectroscopy over the 8.6882(2) s period (MJD 52 663.93) shows clear variations with pulse phase of Γ, while kT_BB shows a small variation of ∼ 12%. We confirm earlier conclusions by Özel (2001, ApJ, 563, 276) that the emission from AXPs is more like ly to originate from neutron stars with one single and magnetically active region on the neutron star. The significantly different behavior of the soft and hard spectral components with pulse phase, however, cannot be fully reconciled with the present magnetar emission models.