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CATEGORIES:DAMTP Astrophysics Seminars
SUMMARY:A new accretion disc instability and measuring the
  inner torque of a relativistic disc - Dr. William
  Potter (University of Oxford)
DTSTART;TZID=Europe/London:20141103T160000
DTEND;TZID=Europe/London:20141103T170000
UID:TALK52614AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/52614
DESCRIPTION:In the first part of the talk I will introduce a d
 isc instability caused by a variable alpha paramet
 er. The alpha parameter is expected from theory an
 d simulations to depend on the detailed plasma pro
 perties\, in particular\, the magnetic Prandtl num
 ber. I will show that a variable alpha can lead to
  a disc instability resulting in limit cycle behav
 iour and flaring (analogous to the hydrogen ionisa
 tion instability in dwarf novae). This new instabi
 lity is likely to be important in explaining the c
 omplex outbursts of X-ray binary systems. In the s
 econd part of the talk I will show that the functi
 onal form of the high frequency tail of a relativi
 stic Novikov-Thorne disc spectrum depends on the s
 ize of the inner torque on the disc. Measuring the
  inner torque acting on accretion discs is importa
 nt in understanding the physics in the plunging re
 gion and relativistic jet production. I demonstrat
 e this difference numerically using a ray-tracing 
 code utilising adaptive mesh refinement.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberf
 orce Road\, Cambridge
CONTACT:Adrian Barker
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