Optical spectroscopic monitoring of the variation in the circumstellar disc in PSR B1259-63/LS 2883 during the 2014 periastron passage

Abstract

Theγ -ray binary system PSR B1259-63/LS 2883 passed through periastron in May of 2014 and was the focus of intensive multiwavelength campaigns. During the previous periastron, a large flare was detected at GeV energies 30 days after the 2010 periastron passage by Fermi-LAT. This event was re-detected during 2014 at a similar orbital phase. In order to place better constraints on the behaviour of the circumstellar disc around periastron, we performed optical spectroscopy of the Hα and He i (λ6678) lines with the Southern African Large Telescope (SALT) from 33 days before until 78 days after the 2014 periastron. The Hα line remains single peaked through all observations, but with a noted asymmetry and variation in shape. The He i line remains double peaked and shows a variation in the relative peak heights. Both lines show an increase in the equivalent width which peaks after periastron. The line strengths before periastron are, however, weaker than were detected around the 2010 periastron, though are comparable after periastron.