Studying timing properties of low-mass X-ray binaries with NICER and Swift

The X-ray Timing Instrument of the Neutron star Interior Composition Explorer (NICER) allows investigating short-term variability of compact objects in the soft (0.2-12 keV) X-ray band. NICER's flexibility combined with its large collection area at low energies has provided a new view of the properties and evolution of the inflows and outflows of matter in these systems. We used publicly available NICER monitoring data of several black hole X-ray binaries candidates, including MAXI J1535-571 and MAXI J1820+070, to follow their outbursts. We present our findings on outburst evolution, quasi-periodic oscillations, and state transitions. We highlight the behavior of individual sources and discuss peculiarities. MAXI J1820+070, for example, showed in many observations type-C quasi-periodic oscillations with a characteristic frequencies below 1 Hz. This finding suggests that the source stayed in a state of low effective accretion for large parts of its outburst. In addition, we present the results of our study of covariance spectra and of multi-waveband studies based on Swift/UVOT data, and discuss implications.