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

Abstract

The black hole transient V404 Cygni exhibited a bright outburst in June 2015 that was intensively followed over a wide range of wavelengths. Our team obtained high time resolution optical spectroscopy (∼ 90 s), which included a detailed coverage of the most active phase of the event. We present a database consisting of 651 optical spectra obtained during this event, that we combine with 58 spectra gathered during the fainter December 2015 sequel outburst, as well as with 57 spectra from the 1989 event. We previously reported the discovery of wind-related features (P-Cygni and broad-wing line profiles) during both 2015 outbursts. Here, we build diagnostic diagrams that enable us to study the evolution of typical emission line parameters, such as line fluxes and equivalent widths, and develop a technique to systematically detect outflow signatures. We find that these are present throughout the outburst, even at very low optical fluxes, and that both types of outflow features are observed simultaneously in some spectra, confirming the idea of a common origin. We also show that the nebular phases depict loop patterns in many diagnostic diagrams, while P-Cygni profiles are highly variable on time-scales of minutes. The comparison between the three outbursts reveals that the spectra obtained during June and December 2015 share many similarities, while those from 1989 exhibit narrower emission lines and lower wind terminal velocities. The diagnostic diagrams presented in this work have been produced using standard measurement techniques and thus may be applied to other active low-mass X-ray binaries.

An equatorial outflow in the black hole optical dipper Swift J1357.2−0933

“…This is interpreted as the signature of hot equatorial winds. In the optical, P-Cygni profiles have been reported in V404 Cygni, V4641 Sgr and MAXI J1820+070, demonstrating the presence of low-ionisation winds with terminal velocities in the range of 1000−3000 km s −1 Mata Sánchez et al 2018;Muñoz-Darias et al 2018. Thus, the terminal velocity that we measure in Swift J1357.2-0933 is consistent with the upper end of wind-type outflows observed in other BHTs.…”

Hard-state Accretion Disk Winds from Black Holes: The Revealing Case of MAXI J1820+070

“…1 top panel) reaching ∼ 1200 km s −1 , hence very similar to v t measured from P-Cyg absorptions before and after these epochs. This behaviour has been also witnessed in V404 Cyg (Mata Sánchez et al 2018) and we interpret these features as wind detections. The remaining epochs, including every soft state observation ( Fig.…”

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).…”

“…Given its strength, Hα is the best feature to search for the latter. To this end, we have computed the diagnostic diagram developed in Mata Sánchez et al (2018) for V404 Cyg and subsequently refined in Muñoz-Darias et al (2019b) for MAXI J1820+070, to which we refer the reader for further details. We performed a Gaussian fit to the Hα line profile masking the innermost part of the line (-500 to 500 km s −1 in velocity scale), subtracted the fit from the data, and measured the equivalent width (EW) of the residuals in the blue (-2000 to -1000 km s −1 ) and red (1000 to 2000 km s −1 ) emission line wings.…”