MAXI J1348-630: SALT optical spectroscopy during outburst

ATel #12480; P. A.Charles (Southampton), D. A.H. Buckley, E. Kotze, S. B.Potter, J. K.Thomas (SAAO/SALT), P. Gandhi, J. A.Paice (Southampton)
on 7 Feb 2019; 20:35 UT
Credential Certification: Phil Charles (pac2soton@gmail.com)

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Following the discovery (ATEL #12425) and subsequent optical identification (ATEL #12430) of MAXI J1348-630, we have undertaken intermediate dispersion spectroscopy of the optical counterpart with the Robert Stobie Spectrograph on SALT, in Sutherland, South Africa, as part of the SALT Transients programme. We obtained 3 spectra (exposure times 1200s, 2x1600s) on 2019 Jan 29 and 30 (UT 00-01h) using the G0900 grating, covering the spectral range 4200-7300Å at a resolving power of ~1000 (spectral resolution ~6.5Å) and under good observing conditions.

All spectra are largely featureless, apart from relatively weak H, HeII emission lines and interstellar absorption features. We find broad (~700 km/s), single-peaked emission at Hα (EW~3Å), plus broad HeII emission (EW~2Å) and the Bowen blend. The continuum appears reddened, as intimated in ATEL #12439 and #12456, and we find diffuse interstellar absorption at 4430Å (EW=2.25Å), 6283Å and the NaD lines (EW=2.0Å). Assuming standard interstellar absorption parameters for the 4430Å DIB (Herbig 1975 ApJ 196, 129) and NaD lines (Barbon et al 1990 A&A 237, 79), this implies an A_v of ~2-3 mags, consistent with the X-ray absorbing column of ~7x10²¹ cm^-2 inferred from Swift observations quoted in ATEL #12439.

Our spectra are similar to other LMXB X-ray transients in outburst, and if it is a BH system (ATEL #12447) then it is likely at a distance >3kpc (ATEL #12439), again consistent with the reddening given its galactic latitude (-1.4 degs). Further spectroscopic study is encouraged as the outburst progresses, and especially into quiescence.