Observationally-Inspired Observationally-Inspired Simulations of the Disk-Jet Simulations of the Disk-Jet

Interaction in GRS 1915+105Interaction in GRS 1915+105

David RothsteinDavid RothsteinCornell UniversityCornell University

with assistance from Richard Lovelace (Cornell University)

The Basic IdeaThe 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)Question (for starters)

What happens when the turbulence in a What happens when the turbulence in a steady accretion disk increases rapidly?steady accretion disk increases rapidly?

AnswerAnswer

The disk goes into an outburst that The disk goes into an outburst that matches observational data better than the matches observational data better than the

standard limit cycle instability.standard limit cycle instability.

~ 20 min ~ 20 min (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?Why Increase the Turbulence Rapidly?Theoretical reasonsTheoretical reasons

Models for steady jets typically require strong, Models for steady jets typically require strong, large-scale magnetic fieldslarge-scale magnetic fields

Tagger et al. 2004: Destruction of the magnetic Tagger et al. 2004: Destruction of the magnetic field field (when a transient jet is ejected)(when a transient jet is ejected) could cause could cause the magnetorotational instability (MRI) that drives the magnetorotational instability (MRI) that drives turbulence to become operableturbulence to become operable

Our WorkOur Work

One-dimensionalOne-dimensional simulations of a standard disk simulations of a standard disk(since timescale of interest is ~10(since timescale of interest is ~1077 orbital periods…) orbital periods…)

To model an increase in turbulence, we force the To model an increase in turbulence, we force the Shakura & Sunyaev (1973) Shakura & Sunyaev (1973) αα parameter to parameter to increaseincrease

All simulations begin with All simulations begin with αα = 0.01 (steady disk = 0.01 (steady disk with MRI suppressed) and increase to with MRI suppressed) and increase to αα = 0.1 = 0.1 (MRI “turns on”)(MRI “turns on”)

Increasing the turbulence in Increasing the turbulence in the inner disk the inner disk leads toleads to an an

outburst (and transition wave)outburst (and transition wave)

Local Energy Balance AnalysisLocal Energy Balance Analysis

heating

cooling

Local Energy Balance AnalysisLocal Energy Balance Analysis

Inner Disk

Outer Disk

Black Curve = initial state (low turbulence) Blue Curve = final state (high turbulence)

Classic Limit Cycle InstabilityClassic Limit Cycle Instability

Outburst occurs due to high external accretion rate Outburst occurs due to high external accretion rate (inner disk (inner disk inherently unstableinherently unstable))

Transition wave stalls after ~ 150-200 rTransition wave stalls after ~ 150-200 rgravgrav and outburst and outburst ends after ~ 20-30 seconds (for ends after ~ 20-30 seconds (for αα = 0.1 disk) = 0.1 disk)(e.g., Honma et al. 1991; Szuszkiewicz & Miller 1998, 2001)(e.g., Honma et al. 1991; Szuszkiewicz & Miller 1998, 2001)

Increasing turbulence can give Increasing turbulence can give longerlonger or or shortershorter outbursts; outbursts; transition wave generally transition wave generally

propagates within the region propagates within the region where turbulence is increased where turbulence is increased

(i.e., where jet is ejected)(i.e., where jet is ejected)

Outburst Light CurvesOutburst Light Curves

Turbulence increased within inner ~400 rgrav

Turbulence increased within inner ~100 rgrav

Classic Limit Cycle InstabilityClassic Limit Cycle Instability

Get repeating outbursts “forever” (until external Get repeating outbursts “forever” (until external accretion rate decreases)accretion rate decreases)

Increasing turbulence can give Increasing turbulence can give a wider variety of behavior:a wider variety of behavior:

• Single outburst, then returns Single outburst, then returns to a stable stateto a stable state

• Repeating outbursts with Repeating outbursts with initial outburst longer?initial outburst longer?

What if Turbulence is What if Turbulence is Increased in the Middle Increased in the Middle

Part of the Disk Only?Part of the Disk Only?

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

Delayed Outbursts:Delayed Outbursts:Observational Counterparts?Observational Counterparts?

(Eikenberry et al. 2000 and Rothstein et al. 2005)(Eikenberry et al. 2000 and Rothstein et al. 2005)

Infrared

X-ray

ConclusionsConclusions

Rapid increase in turbulence (Rapid increase in turbulence (αα parameter) is a parameter) is a new way to drive an accretion disk into outburstnew way to drive an accretion disk into outburst

Key ingredient for the big outbursts:Key ingredient for the big outbursts:Energy balance curve must change faster than Energy balance curve must change faster than thermal timescalethermal timescale

If the change is caused by an ejection, this If the change is caused by an ejection, this requires requires jet velocity >> jet velocity >> αα x (sound speed) x (sound speed) … … easy condition to meet!easy condition to meet!