Inclination dependence of QPO phase lags in black hole X-ray binaries

Understand

Quasi-periodic oscillations (QPOs) with frequencies from $\sim0.05$-$30$ Hz are a common feature in the X-ray emission of accreting black hole binaries.

• As the QPOs originate from the innermost accretion flow, they provide the opportunity to probe the behaviour of matter in extreme gravity.
• In this paper, we present a systematic analysis of the inclination dependence of phase lags associated with both Type-B and Type-C QPOs in a sample of 15 Galactic black hole binaries.
• We find that the phase lag at the Type-C QPO frequency strongly depends on inclination, both in evolution with QPO frequency and sign.