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Spectral Hardening of the Accretion Disk in Black Hole X-ray Binaries: Implications for X-ray Transients and Black Hole Spin

Event Details

Event Dates: 

Friday, February 21, 2014 - 12:00pm

Seminar Location: 

  • CASA Conference Room C324

Speaker Name(s): 

Greg Salvesen

Speaker Affiliation(s): 

JILA
Seminar Type/Subject

Scientific Seminar Type: 

  • Astrophysics Lunch Seminar

Event Details & Abstract: 

The X-ray spectrum of the accretion disk around a black hole in an X-ray binary can be well-fit with a standard multi-color blackbody disk model. From this model fit, X-ray observers derive the location of the inner edge of the accretion disk. The extent to which the inner disk is truncated is a powerful observational diagnostic that can be used to understand how the disk behaves in transient episodes and to measure the angular momentum (a.k.a. spin) of the black hole. An often overlooked caveat when fitting the X-ray spectrum of an accretion disk is the degree to which physical effects, such as Comptonization and the disk vertical structure, act to harden the seed accretion disk spectrum. My talk will address two important consequences of dismissing the role of spectral hardening in the observed accretion disk spectrum. These are: (1) Allowing hardening processes to evolve during black hole transient episodes can explain the observed accretion disk evolution without the need for invoking a mobile inner disk edge. (2) Measurements of black hole spin change drastically for small deviations from the canonically assumed amount of disk spectral hardening. Lastly, I will briefly outline additional work that I am pursuing to quantify spectral hardening of the accretion disk in black hole X-ray binaries.