Rms-spectra study of Low-frequency QPOs in Black hole binary sytems using NICER

It is eminent that the low-frequency QPOs ranging from 0.1-30.0 Hz are observed in the hard or hard-intermediate state of Blackhole X-ray binaries. On the basis of Q-factor and the presence of harmonic, sub-harmonic and Broad Lorentzian noise they have been classified into A, B and C type of QPOs. The C-type QPO is very common and generally seen in the hard state and the B-type QPO, which is less common appears in hard-soft transition states. The earlier study of rms spectra for B and C type of QPOs with RXTE suggest that the origin of the two types of QPOs are different. In this work, we inspect the NICER archival observations of Blackhole sources in which B or C-type of QPOs was present and studied the rms-lag spectra.