XMM-Newton spectroscopy of the accreting magnetar candidate 4U0114+65

Abstract

4U0114$+$65 is one of the slowest known X-ray pulsars. We present an analysis of a pointed observation by the XMM-Newton X-ray telescope. The energy-resolved light curve, the time-resolved X-ray spectra provided by the EPIC cameras on board and the first high-resolution spectrum of this source, provided by the Reflection Grating Spectrometer, were analysed. An X-ray pulse of $9350\pm 160$ s was measured, confirming the secular spin up of this source. We also fit the pulse-phase-resolved spectra with Comptonisation models. These models imply a very small ($r\sim 3$ km) and hot ($kT\sim 2-3$ keV) emitting region and therefore point to a hot spot over the neutron star (NS) surface as the most reliable explanation for the X-ray pulse. The long NS spin period, the spin-up rate, and persistent X-ray emission can be explained within the theory of quasi-spherical settling accretion, which may indicate that the magnetic field is in the magnetar range. Thus, 4U 0114$+$65 could be a wind-accreting magnetar. We also observed two episodes of low luminosity. The first can be explained as an absorption by an over-dense structure in the wind of the donor. The second episode may be due to temporal cessation of accretion onto one magnetic pole caused by non-spherical matter capture from the structured stellar wind. The light curve displays two types of dips seen during the high-flux intervals. The short dips, with durations of tens of seconds, are produced through absorption by wind clumps. The long dips might be associated with the rarefied interclump medium. We also found evidence of emission lines in the X-ray photoionised wind of the B1Ia donor. The Fe K$\alpha$ line is highly variable and much weaker than in other X-ray binaries with supergiant donors. The degree of wind clumping, measured through the covering fraction, is much lower than in supergiant donor stars with earlier spectral types.

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• High-resolution X-ray spectroscopy of the stellar wind in Vela X-1 during a flare
• X-ray variability of the HMXB Cen X-3: evidence for inhomogeneous accretion flows
• Understanding the coexistence of spin-up and spin-down behaviors in long period X-ray pulsars
• Are there magnetars in high-mass X-ray binaries?
• Cyclical accretion regime change in the slow X-ray pulsar 4U 0114+65 observed with Chandra
• Nustar observation of the binary system 4U 0114+65
• A study of the accretion mechanisms of the High Mass X-ray Binary IGR J00370+6122