Determination of the turbulent parameter in accretion discs: effects of self-irradiation in 4U 1543−47 during the 2002 outburst

Abstract

We investigate the viscous evolution of the accretion disk in 4U 1543−47, a black hole binary system, during the first 30 days after the peak of the 2002 burst by comparing the observed and theoretical accretion rate evolutionṀ(t). The observedṀ(t) is obtained from spectral modelling of the archival RXTE/PCA data. Different scenarios of disk decay evolution are possible depending on a degree of self-irradiation of the disk by the emission from its centre. If the self-irradiation, which is parametrized by factor C irr , had been as high as ∼ 5 × 10 −3 , then the disk would have been completely ionized up to the tidal radius and the short time of the decay would have required the turbulent parameter α ∼ 3. We find that the shape of theṀ(t) curve is much better explained in a model with a shrinking high-viscosity zone. If C irr ≈ (2 − 3) × 10 −4 , the resulting α lie in the interval 0.5 − 1.5 for the black hole masses in the range 6 − 10 M , while the radius of the ionized disk is variable and controlled by irradiation. For very weak irradiation, C irr < 1.5 × 10 −4 , the burst decline develops as in normal outbursts of dwarf novae with α ∼ 0.08 − 0.32. The optical data indicate that C irr in 4U 1543−47 (2002) was not greater than approximately (3−6)×10 −4 . Generally, modelling of an X-ray nova burst allows one to estimate α that depends on the black hole parameters. We present the public 1-D code freddi to model the viscous evolution of an accretion disk. Analytic approximations are derived to estimate α in X-ray novae usingṀ(t).

Understanding X-ray irradiation in low-mass X-ray binaries directly from their light-curves

“…The 2002 outburst of 4U 1543−564 is the only outburst (of the 15 in this paper) where C irr has been estimated previously. Comparing the optical/near-infrared and X-ray lightcurves, Lipunova & Malanchev (2017) find C irr < 6 × 10 −4 , which is in conflict with our measurement of C irr = 1.16 +0.99 −0.69 . This is one of the sources where we find a linear decay timescale τ l and the exponential decay timescale τ e that differ significantly.…”

“…This is one of the sources where we find a linear decay timescale τ l and the exponential decay timescale τ e that differ significantly. While this may point to an issue with the simplifying assumptions in King & Ritter (1998), this outburst remains difficult to fit when the formalism of Lipunova & Shakura (2000) and Lipunova & Malanchev (2017) is adopted. Lipunova & Malanchev (2017) attempted to fit theoretical lightcurves to the outburst: either L bol ∝ t −10/3 for a viscous decay (our "exponential" decay) or L bol ∝ (t − t end ) 40/13 for an irradiation-controlled decay (our "linear" decay), where t end is the time the source returns to quiescence.…”

On the physical nature of accretion disc viscosity

“…Malanchev & Shakura (2015) modeled the light curve of A0620-00 1975 and found α ≈ 0.5 − 0.6. Lipunova & Malanchev (2017) modeled the accretion disc in 4U 1543-37 during the 2002 outburst and compared with the accretion rate that is observed from spectral modeling of data from the RXTE observatory. They found that the value for α in X-ray binary outbursts depends upon the self-irradiation, but all models suggest that α 0.1.…”

Thermally driven disc winds as a mechanism for X-ray irradiation heating in black hole X-ray binaries: the case study of GX339–4

“…However, the use of simultaneous multi-wavelength data sets does provide a promising alternative approach. By modelling the irradiated discs in BH-LMXBs, assuming a constant irradiation geometry, values of C ∼ 6 × 10 −4 − 7 × 10 −3 have been found to sufficiently explain the observed multi-wavelength outburst behaviour in a small sample of systems (e.g., Hynes et al 2002;Suleimanov et al 2008;Lipunova & Malanchev 2017). However, evidence also exists suggesting the possibility that C may change between the hard and soft accretion states (e.g., Gierliński et al 2009;Kimura & Done 2019).…”