Mass Measurements of Black Holes in X-Ray Transients: Is There a Mass Gap?

Understand

We explore possible systematic errors in the mass measurements of stellar mass black holes.

• We find that significant errors can arise from the assumption of zero or constant emission from the accretion flow, which is commonly used when determining orbital inclination by modelling ellipsoidal variations.
• For A0620-00, the system with the best available data, we show that typical data sets and analysis procedures can lead to systematic underestimates of the inclination by ten degrees or more.
• A careful examination of the available data for the 15 other X-ray transients with low-mass donors suggests that this effect may significantly reduce the black hole mass estimates in several other cases, most notably that of GRO J0422+32.