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SUMMARY:A new accretion disc instability and measuring the inner torque of
  a relativistic disc - Dr. William Potter (University of Oxford)
DTSTART:20141103T160000Z
DTEND:20141103T170000Z
UID:TALK52614@talks.cam.ac.uk
CONTACT:Adrian Barker
DESCRIPTION:In the first part of the talk I will introduce a disc instabil
 ity caused by a variable alpha parameter. The alpha parameter is expected 
 from theory and simulations to depend on the detailed plasma properties\, 
 in particular\, the magnetic Prandtl number. I will show that a variable a
 lpha can lead to a disc instability resulting in limit cycle behaviour and
  flaring (analogous to the hydrogen ionisation instability in dwarf novae)
 . This new instability is likely to be important in explaining the complex
  outbursts of X-ray binary systems. In the second part of the talk I will 
 show that the functional form of the high frequency tail of a relativistic
  Novikov-Thorne disc spectrum depends on the size of the inner torque on t
 he disc. Measuring the inner torque acting on accretion discs is important
  in understanding the physics in the plunging region and relativistic jet 
 production. I demonstrate this difference numerically using a ray-tracing 
 code utilising adaptive mesh refinement.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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