Volume 646, February 2021
|Number of page(s)||9|
|Published online||19 February 2021|
A variable magnetic disc wind in the black hole X-ray binary GRS 1915+105?
Department of Physics, Tor Vergata University of Rome, Via della Ricerca Scientifica 1, 00133 Rome, Italy
2 INAF – IAPS, Via Fosso del Cavaliere 100, 00133 Rome, Italy
3 INAF – Astronomical Observatory of Rome, Via Frascati 33, 00078 Monte Porzio Catone (Rome), Italy
4 INFN – Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
5 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
6 NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
7 James Madison University, 800 South Main Street, Harrisonburg, VA 22807, USA
Accepted: 14 December 2020
Context. GRS 1915+105 being one of the brightest transient black hole binaries (BHBs) in the X-rays offers a unique testbed for the study of the connection between accretion and ejection mechanisms in BHBs. In particular, this source can be used to study the accretion disc wind and its dependence on the state changes in BHBs.
Aims. Our aim is to investigate the origin and geometry of the accretion disc wind in GRS 1915+105. This study will provide a basis for planning future observations with the X-ray Imaging Spectroscopy Mission (XRISM), and may also provide important parameters for estimating the polarimetric signal with the upcoming Imaging X-ray Polarimetry Explorer (IXPE).
Methods. We analysed the spectra of GRS 1915+105 in the soft ϕ and hard χ classes using the high-resolution spectroscopy offered by Chandra HETGS. In the soft state, we find a series of wind absorption lines that follow a non-linear dependence of velocity width, velocity shift, and equivalent width with respect to ionisation, indicating a multiple component or stratified outflow. In the hard state we find only a faint Fe XXVI absorption line. We model the absorption lines in both the states using a dedicated magneto-hydrodynamic (MHD) wind model to investigate a magnetic origin of the wind and to probe the cause of variability in the observed line flux between the two states.
Conclusions. The MHD disc wind model provides a good fit for both states, indicating the possibility of a magnetic origin of the wind. The multiple ionisation components of the wind are well characterised as a stratification of the same magnetic outflow. We find that the observed variability in the line flux between soft and hard states cannot be explained by photo-ionisation alone but is most likely due to a large (three orders of magnitude) increase in the wind density. We find the mass outflow rate of the wind to be comparable to the accretion rate, suggesting an intimate link between accretion and ejection processes that lead to state changes in BHBs.
Key words: accretion, accretion disks / stars: winds, outflows / magnetohydrodynamics (MHD) / X-rays: binaries
© ESO 2021
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.