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 2004 July 4 and 2005 March 28, which cover the minor outburst of the star in early 2004 July and quiescence variations on 19 nights scattered over six months. During the outburst, the star peaked approximately 3 mag 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 Hα line had multiple components, one being a broad blueshifted wing exceeding 5000 km s−1. During a simultaneously observed 10‐min photometric flare up, the equivalent width of the Hα 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 (K2= 211.3 ± 1.0 km s−1), within errors, as Orosz et al., our centre‐of‐mass velocity (γ= 72.7 ± 3.3 km s−1) differs significantly from the previously published value (107.4 ± 2.9 km s−1). 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.

The 1989 and 2015 outbursts of V404 Cygni: a global study of wind-related optical features

“…Miller et al 2008). In addition, the fourth in this list would be V4641 Sgr, for which Muñoz-Darias, Torres & Garcia (2018) have recently found conclusive evidence for optical winds with very similar properties to that of V404 Cyg (see also Chaty et al 2003;Lindstrøm et al 2005). Finally, we note that an alike accretion/outflow coupling, including winds, is likely present in neutron star systems (e.g.…”

The low-luminosity accretion disc wind of the black hole transient V4641 Sagittarii

“…It has also one of the longest orbital periods and therefore accretion discs after GRS 1915+105 (which is showing a quasi-persistent behaviour) and V404 Cyg itself. As noted in MD16, V4641 Sgr is, within the known population of BHTs, the one which has displayed optical phenomenology more similar to that of V404 Cyg, with broad Hα emission and weak P-Cygni profiles in Fe ii at 5169Å with a terminal velocity of ∼ 600 km s −1 (Lindstrøm et al 2005;Chaty et al 2003). In this paper we present an optical spectroscopic study carried out over the 1999 discovery outburst (in't Zand et al 2000), as well as the 2002 and 2004 events.…”

The Changing-look Optical Wind of the Flaring X-Ray Transient Swift J1858.6-0814

“…Furthermore, intense and sensitive spectroscopic campaigns carried out over the last few years have unveiled the presence of optical winds in several BH (R1000B and R2500R, respectively) transients. P-Cyg profiles have been discovered in V404 Cyg Muñoz-Darias et al 2017;Mata Sánchez et al 2018; see also Casares et al 1991 for detections during the 1989 outburst) and MAXI J1820+070 , while an archival search showed the presence of conspicuous wind signatures in several outbursts of V4641 Sgr ; see Lindstrøm et al 2005 andChaty et al 2003 for earlier reports). In addition, the classical systems GRO J1655-40 and GX 339-4 showed complex emission line profiles (Soria et al 2000;Rahoui et al 2014, respectively), while the intriguing optical dips of Swift J1357.2-0933 (Corral-Santana et al 2013) have recently been found to be related to disk outflows seen at high orbital inclination (Jiménez-Ibarra et al 2019a;Charles et al 2019).…”