2021MNRAS.508.3104B

MAXI J1820+070 (ASSASN-18ey) is a black hole (BH) X-ray binary discovered in 2018. The brightness of the source triggered multi-wavelength campaigns of this source from different observatories. We analyse the power density spectra (PDS) obtained from NICER high cadence observations of the source in the hard state. We obtain the evolution of the characteristic frequencies by modelling the PDS. We interpret the characteristic frequencies of various PDS components (both QPOs and broad-band noise components) as variability occurring at a particular radius, and explain them in the context of the Relativistic Precession Model (RPM). We estimate the dimensionless spin of the BH at 0.799^+0.016_–0.015 by fitting the RPM.