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

Monthly Notices of the Royal Astronomical Society

Muñoz-Darias

Casares

et al. 2019

We present high-time resolution optical spectroscopy and imaging of the black hole transient Swift J1357.2-0933 during its 2017 outburst. The light curves show recurrent dips resembling those discovered during the 2011 outburst. The dip properties (e.g duration and depth) as well as the evolution of their recurrence time are similar to those seen in 2011. Spectra obtained during the dips are characterised by broad and blue-shifted absorptions in Balmer and He ii. The absorptions show core velocities of ∼ −800 km s −1 and terminal velocities approaching ∼3000 km s −1 i.e. in the upper-end of wind velocities measured in other black hole transients (both at optical and X-ray wavelengths). Our observations suggest that the dips are formed in a dense and clumpy outflow, produced near the disc equatorial plane and seen at high inclination. We also study the colour evolution and observe that, as it has been previously reported, the source turns bluer during dips. We show that this is due to a gradual change in the slope of the optical continuum and discuss possible implications of this behaviour.

Section: Discussionsupporting

confidence: 89%

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

Monthly Notices of the Royal Astronomical Society

Muñoz-Darias

Casares

et al. 2019

“…Muñoz-Darias et al (2019) presented the discovery of an accretion disc outflow during the hard state of the outburst of J1820. This result, together with previous findings on the long-orbital period (> 2 d) BH transients V404 Cyg and V4641 Sgr ,Muñoz-Darias et al 2018, shows that winds are likely a common feature of BH transients in outburst. Our determination of a 0.68 d orbital period for J1820, however, seems to indicate that the presence of winds is not limited to the BH transients with the largest accretion discs.…”

Section: Discussionsupporting

confidence: 84%

Dynamical Confirmation of a Black Hole in MAXI J1820+070

Torres

Casares

et al. 2019

ApJL

108

102

We present time-resolved 10.4-m GTC and 4.2-m WHT intermediate resolution spectroscopy of the X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained during its decline to the quiescent state. Cross-correlation of the 21 individual spectra against late-type templates reveals a sinusoidal velocity modulation with a period of 0.68549 ± 0.00001 d and semi-amplitude of 417.7 ± 3.9 km s −1 . We derive a mass function f(M)=5.18 ± 0.15 M , dynamically confirming the black hole nature of the compact object. Our analysis of the stellar absorption features supports a K3 − 5 spectral classification for the donor star, which contributes ≈ 20% of the total flux at 5200-6800Å. The photometric 0.703 ± 0.003 d periodicity observed during outburst is 2.6 % longer than the orbital period supporting the presence of a superhump modulation in the outburst light curves. In line with this interpretation, we constrain the binary mass ratio to be q 0.12. In addition, we observe a sharp increase in the Hα emission line equivalent width during inferior conjunction of the donor star that we interpret as a grazing eclipse of the accretion disc and allows us to constrain the binary inclination to i 69 • . On the other hand, the absence of X-ray eclipses during outburst imply i 77 • . These inclination limits, together with our dynamical solution, lead to a black hole mass in the range 7-8 M . We also measure a systemic velocity γ = −21.6 ± 2.3 km s −1 which, combined with the Gaia DR2 proper motion and parallax, implies a large peculiar velocity ∼100 km s −1 .

“…As recently discussed in Hare et al (2020), the strong flaring activity and variable X-ray absorption of Swift J1858.6-0814 (see also Ludlam et al 2018;Reynolds et al 2018) resembles the behaviour of V404 Cyg and V4641 Sgr (see e.g. Kimura et al 2016;Motta et al 2017;Morningstar et al 2014;Gallo et al 2014;Muñoz-Darias et al 2018). These two objects display non-standard outbursts characterised by sharp rising phases followed by significant luminosity drops and the absence of steady soft states (e.g.…”

Section: Discussionmentioning

confidence: 67%

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

Muñoz-Darias

Padilla

et al. 2020

ApJL

We present the discovery of an optical accretion disk wind in the X-ray transient Swift J1858.6-0814. Our 90-spectrum data set, taken with the 10.4m GTC telescope over 8 different epochs and across five months, reveals the presence of conspicuous P-Cyg profiles in He i at 5876Å and Hα. These features are detected throughout the entire campaign, albeit their intensity and main observational properties are observed to vary on time-scales as short as five minutes. In particular, we observe significant variations in the wind velocity, between a few hundreds and ∼ 2400 km s −1 . In agreement with previous reports, our observations are characterised by the presence of frequent flares, although the relation between the continuum flux variability and the presence/absence of wind features is not evident. The reported high activity of the system at radio waves indicates that the optical wind of Swift J1858.6-0814 is contemporaneous with the radio-jet, as is the case for the handful of X-ray binary transients that have shown so far optical P-Cyg profiles. Finally, we compare our results with those of other sources showing optical accretion disk winds, with emphasis on V404 Cyg and V4641 Sgr, since they also display strong and variable optical wind features as well as similar flaring behaviour.