The outburst duration and duty cycle of GRS 1915+105

The extraordinarily long outburst of GRS 1915+105 makes it one of the most remarkable low-mass X-ray binaries (LMXBs). It has been in a state of constant outburst since its discovery in 1992, an eruption which has persisted ∼100 times longer than those of more typical LXMBs. The long orbital period of GRS 1915+105 implies that it contains large and massive accretion disc which is able to fuel its extreme outburst. In this paper, we address the longevity of the outburst and quiescence phases of GRS 1915+105 using smooth particle hydrodynamics (SPH) simulations of its accretion disc through many outburst cycles. Our model is set in the two-α framework and includes the effects of the thermoviscous instability, tidal torques, irradiation by central X-rays and wind mass loss. We explore the model parameter space and examine the impact of the various ingredients. We predict that the outburst of GRS 1915+105 should last a minimum of 20 yr and possibly up to ∼100 yr if X-ray irradiation is very significant. The predicted recurrence times are of the order of 104 yr, making the X-ray duty cycle a few 0.1 per cent. Such a low duty cycle may mean that GRS 1915+105 is not an anomaly among the more standard LMXBs and that many similar, but quiescent, systems could be present in the Galaxy.