Quasi-periodic Oscillations in Black Hole X-ray Binaries

Sufficiently massive stars end their lives as black holes, which may be surrounded by an accretion disk,

formed by drawing material from the outer layers of a companion star. As the hot (>107 K) and ionized

accreted gas spirals in closer to the black hole, a significant fraction of the liberated gravitational

potential energy is radiated away as light. Such systems are known as black hole x-ray binary (BHBs)

because the radiation is primarily in the X-ray regime. BHBs are observed to dim and brighten at almost

regular intervals, with frequencies ranging from 40 Hz to 450 Hz, in a phenomenon called quasi-periodic

oscillations (QPO). While the frequencies are thought to depend only on fundamental black hole

properties such as mass and spin, the strength (brightness) and sharpness (coherence) of QPO power

spectra are poorly understood. In this work we study the dependence of properties of the QPO power

spectra peaks on dissipation fraction, which is defined as the fraction of accreted gravitational potential

energy that goes into heating the region around the disk photosphere.