Rothstein MIT 2006

Observationally-Inspired Simulations of the Disk-Jet Interaction in GRS 1915+105: 

Observationally-Inspired Simulations of the Disk-Jet Interaction in GRS 1915+105 David Rothstein Cornell University with assistance from Richard Lovelace (Cornell University)

The Basic Idea: 

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!

Question (for starters): 

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.

Why Increase the Turbulence Rapidly?: 

(Eikenberry et al. 1998; Rothstein et al. 2005) Why Increase the Turbulence Rapidly? Black hole transients (especially GRS 1915+105) undergo rapid state transitions after which the disk variability timescales get faster Disk Disk Jet Jet (?)

Why Increase the Turbulence Rapidly?Theoretical reasons : 

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: 

Our Work One-dimensional simulations of a standard disk (since timescale of interest is ~107 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): 

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

Local Energy Balance Analysis: 

Local Energy Balance Analysis

Local Energy Balance Analysis: 

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

Classic Limit Cycle Instability: 

Classic Limit Cycle Instability Outburst occurs due to high external accretion rate (inner disk inherently unstable) Transition wave stalls after ~ 150-200 rgrav and outburst ends after ~ 20-30 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: 

Outburst Light Curves Turbulence increased within inner ~400 rgrav Turbulence increased within inner ~100 rgrav

Classic Limit Cycle Instability: 

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 Repeating outbursts with initial outburst longer?

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

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): 

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

Delayed Outbursts:Observational Counterparts?(Eikenberry et al. 2000 and Rothstein et al. 2005): 

Delayed Outbursts: Observational Counterparts? (Eikenberry et al. 2000 and Rothstein et al. 2005) Infrared X-ray

Conclusions: 

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!