New clues on outburst mechanisms and improved spectroscopic elements of the black-hole binary V4641 Sagittarii

Abstract

We present spectroscopic observations of the black-hole binary V4641 Sagittarii, obtained between 4th July 2004 and 28th March 2005, which cover the minor outburst of the star in early July 2004 and quiescence variations on 19 nights scattered over six months. During the outburst, the star peaked approximately 3 magnitudes brighter than usual, and our spectra were dominated by broad hydrogen, helium and iron emission lines. The very first spectra showed P Cygni profiles, which disappeared within a few hours, indicating rapid changes in matter ejection. The H-alpha line had multiple components, one being a broad blue-shifted wing exceeding 5000 km/s. During a simultaneously observed 10-min photometric flare-up, the equivalent width of the H-alpha line temporarily decreased, implying that it was a flare of the continuum. The overall spectral appearance was similar to that observed in the 1999 September active phase, which suggests that similar mass-ejection processes were associated with both eruptions. In quiescence, the spectra were those of the early-type secondary star showing its orbital motion around the primary. By measuring cross-correlation radial velocities, we give an improved set of spectroscopic elements. Whereas we measure the same velocity amplitude (K_2=211.3+/-1.0 km/s), within errors, as Orosz et al. (2001), our centre-of-mass velocity (v_gamma=72.7+/-3.3 km/s) differs significantly from the previously published value (107.4+/-m2.9 km/s). However, we find evidence that the difference is caused by a systematic error in data reduction in the previous study, rather than by gravitational effects of an invisible third component.

9 pages, 8 figures, accepted for publication in MNRAS

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• The Black Hole Binary V4641 Sagitarii: Activity in Quiescence & Improved Mass Determinations
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• Ultra-High-Energy Gamma-Ray Bubble around Microquasar V4641 Sgr
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• The Changing-look Optical Wind of the Flaring X-ray Transient Swift J1858.6-0814
• NuSTAR observations of the Transient Galactic Black Hole Binary Candidate Swift J1858.6-0814: A New Sibling of V404 Cyg and V4641 Sgr?
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• Discovery of optical and infrared accretion disc wind signatures in the black hole candidate MAXI J1348-630
• A search for very high-energy flares from the microquasars GRS 1915+105, Circinus X-1, and V4641 Sgr using contemporaneous H.E.S.S. and RXTE observations
• High resolution X-ray spectroscopy of V4641 Sgr during its 2020 outburst
• An Overview of Compact Star Populations and Some of Its Open Problems
• Accretion disc winds in X-ray binaries
• Leptonic and hadronic models of high-energy nebula around V4641 Sgr