Optical spectroscopy of the microquasar GRS 1758-258: a possible intermediate mass system?

Abstract

Context. GRS 1758-258 is one of two prototypical microquasars towards the Galactic Center direction discovered almost a quarter of a century ago. The system remains poorly studied in the optical domain due to its counterpart being a very faint and absorbed target in a crowded region of the sky. Aims. Our aim is to investigate GRS 1758-258 in order to shed light on the nature of the stellar binary components. In particular, the main physical parameters of the donor star, such as the mass or the spectral type, are not yet well constrained. Methods. GRS 1758-258 has remained so far elusive to optical spectroscopy owing to its observational difficulties. Here, we use this traditional tool of stellar astronomy at low spectral resolution with a 10 m class telescope and a long slit spectrograph. Results. An improved spectrum is obtained as compared to previous work. The quality of the data does not allow the detection of emission or absorption features but, nevertheless, we manage to partially achieve our aims comparing the de-reddened continuum with the spectral energy distribution expected from an irradiated disc model and different donor star templates. Conclusions. We tentatively propose that GRS 1758-258 does not host a giant star companion. Instead, a main sequence star with mid-A spectral type appears to better agree with our data. The main impacts of this finding are the possibility that we are dealing with an intermediate mass system and, in this case, the prediction of an orbital period significantly shorter than previously proposed.

arXiv comment5 pages, 6 figures, accepted for publication in A&A

References in corpus (9)

• The quiescent light curve and evolutionary state of GRO J1655-40
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• On the precession of accretion discs in X-ray binaries
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• An Extended and More Sensitive Search for Periodicities in RXTE/ASM X-ray Light Curves
• Accretion states of the Galactic microquasar GRS 1758-258
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• The precessing jets of 1E 1740.7-2942
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Cited by in corpus (6)

• A catalogue of high-mass X-ray binaries in the Galaxy: from the INTEGRAL to the Gaia era
• The Galactic LMXB Population and the Galactic Centre Region
• Early metal enrichment of gas-rich galaxies at z~5
• X-ray spectral and flux variability of the microquasar GRS 1758-258 on timescales from weeks to years
• Broadband X-ray Spectroscopy and Estimation of Spin of the Galactic Black Hole Candidate GRS 1758-258
• Effects of precession versus instabilities on the jets of GRS 1758-258