Strong disk winds traced throughout outbursts in black-hole X-ray binaries

Abstract

Recurring outbursts associated with matter flowing onto compact stellar remnants (such as black holes, neutron stars and white dwarfs) in close binary systems provide a way of constraining the poorly understood accretion process. The light curves of these outbursts are shaped by the efficiency of angular-momentum (and thus mass) transport in the accretion disks, which has traditionally been encoded in a viscosity parameter, α. Numerical simulations of the magneto-rotational instability that is believed to be the physical mechanism behind this transport yield values of α of roughly 0.1-0.2, consistent with values determined from observations of accreting white dwarfs. Equivalent viscosity parameters have hitherto not been estimated for disks around neutron stars or black holes. Here we report the results of an analysis of archival X-ray light curves of 21 outbursts in black-hole X-ray binaries. By applying a Bayesian approach to a model of accretion, we determine corresponding values of α of around 0.2-1.0. These high values may be interpreted as an indication either of a very high intrinsic rate of angular-momentum transport in the disk, which could be sustained by the magneto-rotational instability only if a large-scale magnetic field threads the disk, or that mass is being lost from the disk through substantial outflows, which strongly shape the outburst in the black-hole X-ray binary. The lack of correlation between our estimates of α and the accretion state of the binaries implies that such outflows can remove a substantial fraction of the disk mass in all accretion states and therefore suggests that the outflows correspond to magnetically driven disk winds rather than thermally driven ones, which require specific radiative conditions.

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

“…Chakravorty et al 2013;Bianchi et al 2017;Gatuzz et al 2019). In addition, the presence of a continuous, state-independent wind has been proposed as a viable mechanism to explain the high efficiency of angular momentum removal inferred from fits to X-ray light curves (Tetarenko et al 2018). Low-ionisation (cold) disk winds, on the other hand, have been detected via optical/infrared observations in the luminous and violent outbursts of V404 Cyg [Muñoz-Darias et al 2016 (hereafter MD16), Muñoz-Darias et al 2017;Rahoui et al 2017;Mata Sánchez et al 2018; see also Casares et al 1991] and V4641 Sgr (Chaty et al 2003;Lindstrøm et al 2005;Muñoz-Darias et al 2018).…”

Chandra reveals a possible ultrafast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124

“…In X-ray binary systems (XRBs) a stellar-mass compact object, either a black hole or a neutron star, accretes from an companion star in a close orbit. X-ray binaries come in numerous classes, with different combina-winds can carry away a large fraction of the mass from the accretion flow (Neilsen & Lee 2009;Ponti et al 2012), possibly triggering instabilities in the flow (Begelman et al 1983;Muñoz-Darias et al 2016) and potentially affecting the outburst profiles of transient sources (Tetarenko et al 2018). Similarly, jets can remove accretion power from the X-ray binary and deposit large amounts of energy in the surrounding interstellar medium (Fabrika 2004;Fender et al 2005;Gallo et al 2005;Pakull et al 2010).…”

The connection between the UV/optical and X-ray emission in the neutron star low-mass X-ray binary Aql X-1

“…Tudose et al 2009;Miller-Jones & Sivakoff 2013;Díaz Trigo et al 2018;Gusinskaia et al 2019), we do not deem this scenario very likely. Firstly, it appears that the radio/X-ray correlation in Aql X-1 has a much lower β jet value (Tudose et al 2009;Tetarenko et al 2018;Gusinskaia et al 2019). Moreover, a recent radio/X-ray study, using the largest sample of NS LMXBs to date, also found a lower correlation index for the population as a whole (β jet = 0.44; Gallo et al 2018).…”