Discovery of optical outflows and inflows in the black hole candidate GRS 1716-249

TL;DR

This study reports the detection of variable optical outflows and inflows in the black hole candidate GRS 1716-249 during its 2016-2017 outburst, revealing complex accretion dynamics through spectral line analysis.

Contribution

First detailed optical spectroscopic monitoring of GRS 1716-249 during outburst, identifying transient wind and inflow signatures and proposing a failed wind scenario.

Findings

Detection of accretion disc wind with terminal velocity ~2000 km/s.

Observation of red-shifted absorption indicating inflowing material.

Evidence of variable emission line profiles on timescales of hours.

Abstract

We present optical spectroscopy obtained with the GTC, VLT and SALT telescopes during the decline of the 2016-2017 outburst of the black hole candidate GRS 1716-249 (Nova Oph 1993). Our 18-epoch data set spans 6 months and reveals that the observational properties of the main emission lines are very variable, even on time scales of a few hours. Several epochs are characterised by P-Cyg (as well as flat-top and asymmetric) profiles in the H$\alpha$, H$\beta$ and He II ($\lambda$4686) emission lines, implying the presence of an accretion disc wind, which is likely hot and dense. The wind's terminal velocity ($\sim$2000 km s$^{-1}$) is similar to that observed in other black hole X-ray transients. These lines also show transient and sharp red-shifted absorptions, taking the form of inverted P-Cyg profiles. We argue that these profiles can be explained by the presence of infalling material at $\sim$1300 km s$^{-1}$. We propose a failed wind scenario to explain this inflow and discuss other alternatives, such as obscuration produced by an accretion-related structure (e.g. the gas stream) in a high inclination system.