Observationally-Inspired Simulations of the Disk-Jet Interaction in GRS David Rothstein Cornell University with assistance from Richard Lovelace (Cornell University)

The Basic Idea Hard state (steady jet) We don’t understand so well. SPL state (ejection) We really don’t understand so well. Thermal state (no jet) We understand pretty well! A question that can be tested with observations is: How does the removal of a jet affect the subsequent development of the disk?

Question (for starters) What happens when the turbulence in a steady accretion disk increases rapidly? Answer The disk goes into an outburst that matches observational data better than the standard limit cycle instability.

~ 20 min (Eikenberry et al. 1998; Rothstein et al. 2005) Why Increase the Turbulence Rapidly? Black hole transients (especially GRS ) undergo rapid state transitions after which the disk variability timescales get faster Disk JetJet (?)

Why Increase the Turbulence Rapidly? Theoretical reasons Models for steady jets typically require strong, large-scale magnetic fields Tagger et al. 2004: Destruction of the magnetic field (when a transient jet is ejected) could cause the magnetorotational instability (MRI) that drives turbulence to become operable

Our Work One-dimensional simulations of a standard disk (since timescale of interest is ~10 7 orbital periods…) To model an increase in turbulence, we force the Shakura & Sunyaev (1973) α parameter to increase All simulations begin with α = 0.01 (steady disk with MRI suppressed) and increase to α = 0.1 (MRI “turns on”)

Increasing the turbulence in the inner disk leads to an outburst (and transition wave)

Local Energy Balance Analysis heating cooling

Local Energy Balance Analysis Inner Disk Outer Disk Black Curve = initial state (low turbulence)Blue Curve = final state (high turbulence)

Classic Limit Cycle Instability Outburst occurs due to high external accretion rate (inner disk inherently unstable) Transition wave stalls after ~ r grav and outburst ends after ~ seconds (for α = 0.1 disk) (e.g., Honma et al. 1991; Szuszkiewicz & Miller 1998, 2001) Increasing turbulence can give longer or shorter outbursts; transition wave generally propagates within the region where turbulence is increased (i.e., where jet is ejected)

Outburst Light Curves Turbulence increased within inner ~400 r grav Turbulence increased within inner ~100 r grav

Classic Limit Cycle Instability Get repeating outbursts “forever” (until external accretion rate decreases) Increasing turbulence can give a wider variety of behavior: Single outburst, then returns to a stable state Single outburst, then returns to a stable state Repeating outbursts with initial outburst longer? Repeating outbursts with initial outburst longer?

What if Turbulence is Increased in the Middle Part of the Disk Only?

We Get a Delayed Disk Outburst (see also Lovelace et al. 1994)

Delayed Outbursts: Observational Counterparts? (Eikenberry et al and Rothstein et al. 2005) Infrared X-ray

Conclusions Rapid increase in turbulence ( α parameter) is a new way to drive an accretion disk into outburst Key ingredient for the big outbursts: Energy balance curve must change faster than thermal timescale If the change is caused by an ejection, this requires jet velocity >> α x (sound speed) … easy condition to meet!