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SALT high resolution spectroscopy of GX339-4 in outburst

ATel #10864; D. A.H. Buckley, E. Aydi, M. M. Kotze (SAAO), P. Gandhi, D. Altamirano, P. A. Charles (Southampton) and D. Russell (NYU Abu Dhabi)
on 18 Oct 2017; 15:53 UT
Credential Certification: David Buckley (dibnob@saao.ac.za)

Subjects: Optical, X-ray, Black Hole

High resolution (R = 15,000) spectroscopy of the current outbursting black hole transient GX339-4 (ATel #10797) was obtained with the SALT High Resolution Spectrograph (HRS; Crause et al. 2014, Proc SPIE, 91476) on 2017-09-29 starting at 17:28 UTC, during evening twilight. A 2200 s exposure covering the spectral range 3700-8900 Å was obtained in clear conditions and 1.8" seeing. The data were reduced with the SALT HRS MIDAS pipeline (Kniazev et al. 2016, MNRAS 459, 3068). The typical S/N ratios were in the range 20 (blue) to 30 (red). The only obvious spectral features we found was an H-alpha emission line and the Na D absorption doublet. The former, which was Gaussian shaped and not double-peaked, had a heliocentrically corrected velocity of 6.5 km/s, E.W. = -7.2 ± 1.0 Å and FWHM = 920 ± 100 km/s. We expect the H-alpha E.W. to increase as the outburst progresses, for example see figure 2 of Fender et al., 2009, MNRAS, 393, 1608 (http://adsabs.harvard.edu/abs/2009MNRAS.393.1608F).

The Na D doublet appears to show at least three blue shifted absorption components for each line, ranging in velocity from -12 to -140 km/s, with an E.W. ~2 Å consistent with higher resolution (R = 44,000) observations by Hynes et al., 2004, ApJ 609, 317, using UVES, which were interpreted as interstellar features.

While GX339-4 is no longer visible to SALT, it currently remains observable at southern hemisphere observatories at an airmass < 2 for ~1 h after twilight. Additional spectroscopic observations are therefore encouraged.