Long-term evolution of the neutron-star spin period of SXP 1062

Abstract

Context. The Be/X-ray binary SXP 1062 is of especial interest owing to the large spin period of the neutron star, its large spin-down rate, and the association with a supernova remnant constraining its age. This makes the source an important probe for accretion physics.
Aims: To investigate the long-term evolution of the spin period and associated spectral variations, we performed an XMM-Newton target-of-opportunity observation of SXP 1062 during X-ray outburst.
Methods: Spectral and timing analysis of the XMM-Newton data was compared with previous studies, as well as complementary Swift/XRT monitoring and optical spectroscopy with the SALT telescope were obtained.
Results: The spin period was measured to be P_s = (1071.01 ± 0.16) s on 2012 Oct. 14. The X-ray spectrum is similar to that of previous observations. No convincing cyclotron absorption features, which could be indicative for a high magnetic field strength, are found. The high-resolution RGS spectra indicate the presence of emission lines, which may not completely be accounted for by the SNR emission. The comparison of multi-epoch optical spectra suggest an increasing size or density of the decretion disc around the Be star.
Conclusions: SXP 1062 showed a net spin-down with an average of Ṗ_s = (2.27 ± 0.44) s yr^-1 over a baseline of 915 days.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA and on observations made with the Southern African Large Telescope (SALT).The reduced SALT spectra is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/556/A139