SALT observations of the supernova remnant MCSNR J0127−7332 and its associated Be X-ray binary SXP 1062 in the SMC

Abstract

We report the results of optical spectroscopy of the Small Magellanic Cloud supernova remnant (SNR) MCSNR J0127−7332 and the mass donor Be star, 2dFS 3831, in its associated high-mass X-ray binary SXP 1062 carried out with the Southern African Large Telescope. Using high-resolution long-slit spectra, we measured the expansion velocity of the SNR shell of ≈140 km s−1, indicating that MCSNR J0127−7332 is in the radiative phase. We found that the observed line ratios in the SNR spectrum can be understood if the local interstellar medium is ionized by 2dFS 3831 and/or OB stars around the SNR. We propose that MCSNR J0127−7332 is the result of supernova explosion within a bubble produced by the stellar wind of the supernova progenitor and that the bubble was surrounded by a massive shell at the moment of supernova explosion. We estimated the age of MCSNR J0127−7332 to be ≲10 000 yr. We found that the spectrum of 2dFS 3831 changes with orbital phase. Namely, the equivalent width of the H α emission line decreased by ≈40 per cent in ≈130 d after periastron passage of the neutron star and then almost returned to its original value in the next ≈100 d. Also, the spectrum of 2dFS 3831 obtained closest to the periastron epoch (about 3 weeks after the periastron) shows a noticeable emission line of He II λ4686, which disappeared in the next 2 weeks. We interpret these changes as a result of the temporary perturbation and heating of the disc as the neutron star passes through it.