VLT spectroscopy reveals strong near-infrared wind signatures in GRS 1915+105

ATel #16039; J. Sanchez-Sierras, T. Munoz-Darias (IAC-Tenerife), S. Motta (INAF-Brera), R. Fender (Oxford), A. Bahramian (Curtin)
on 17 May 2023; 09:34 UT
Credential Certification: Teo Muñoz-Darias (teo.munoz-darias@iac.es)

Tweet

The black hole transient GRS 1915+105 entered into a new radio loud phase in late March/early April 2023 (ATel#15968, #15974, #16008). These phases are characterised by continuous radio emission (including strong flares), low X-ray emission (also interrupted by occasional flares) and high, variable absorption (see e.g. Motta et al. 2021, MNRAS 503, 152).

We performed near-infrared spectroscopy of GRS 1915+105 on 12/05/2023 using the infrared arm of the X-shooter spectrograph. The total exposure time was 2400s. The data were reduced using the ESO pipeline v.3.5.0. The telluric correction was performed using Molecfit v.3.0.3.

The combined spectrum shows the presence of strong and broad single-peaked emission lines throughout the spectral range covered by our observations (~10500 to 24500 Angs). The He-I lines (e.g. He-I 10830, He-I 20587 and He-I 21125) show conspicuous blue-shifted absorptions (i.e. P-Cyg line profiles) indicating a wind velocity of ~1000 km/s (blue-edge). The Paschen and Brackett hydrogen series are clearly detected with broad emission line wings reaching the continuum at ~3000 km/s. They also show sharp blue-shifted absorption troughs at 250-750 km/s. We also analysed four VLT+X-shooter observations taken in 2019, also during a radio loud phase. These reveal similarly rich infrared spectra with equally strong wind-related features. In one of these epochs the wind terminal velocity (blue-edge He-I lines) reaches ~3000 km/s.

These observations taken during radio loud phases are in deep contrast to a GTC+EMIR monitoring that we have been carrying out since the X-ray emission from the source significantly dropped in 2018. These spectra were taken in 2018-2022 during radio quiet phases, and are focused on the Br-gamma line (21661 Angs). They show double-peaked emission lines characteristic of low luminosity states.

All in all, near-infrared spectroscopy of GRS 1915+105 indicates a clear connection between strong wind-type outflows and the radio loud phases displayed at low X-ray fluxes (and high intrinsic absorption). We note that both the velocity and the depth of the profiles (in some cases ~30 per cent below the continuum level) are among the strongest observed for cold winds, comparable to those seen in V404 Cyg (Munoz-Darias et al. 2016, Nature, 534, 75) and V4641 Sgr (Munoz-Darias, Torres & Garcia, MNRAS 2018, 479, 3987).

Additional VLT+X-shooter observations are planned for the coming weeks. We are grateful to the VLT team for granting us this DDT program. We are grateful to the VLT and GTC teams for their rapid respond to our triggers.