SALT optical spectroscopic observation of the outbursting Be X-ray binary, 1A 1118-616
ATel #17620; I. M. Monageng (UCT/SAAO), Coe M. J. (Southampton University), D. A.H. Buckley (SAAO/UCT/UFS), Gaudin T. M. (PSU)
on 21 Jan 2026; 18:53 UT
Credential Certification: Itumeleng Monageng (itu@saao.ac.za)
Subjects: Optical, Binary, Transient, Pulsar
The optical counterpart of the Be X-ray binary system A1118-616, which recently experienced an X-ray brightening triggered by Swift/BAT (ATel#17608), was observed using the Southern African Large Telescope (SALT) on January 21, 2026, starting at 00:45:00 UTC. The High Resolution Spectrograph (HRS) was employed in Medium Resolution mode (R~30,000) with a total exposure time of 900 seconds, covering a wavelength range of approximately 3800 to 8800 Angstroms.
The spectrum displays characteristics similar to those observed in previous optical campaigns, with strong Balmer emission lines. The measured equivalent widths (EW) of the H-alpha and H-beta lines are -89.8 ± 2.8 Angstroms and -8.38 ± 0.49 Angstroms, respectively. The H-alpha EW is consistent with the maximum measured value from prior optical observations of the system during a Type II outburst (Coe et al. 1994).
The higher resolution of the newly obtained SALT HRS spectrum reveals structures that were not detectable in earlier observations due to limited spectral resolution. Both the H-alpha and H-beta emission lines exhibit asymmetric double-peak profiles, with red and blue peaks dominating, respectively. This suggests a possible complex geometric disc morphology that could have enabled the enhanced accretion resulting in the X-ray outburst.
