2018ApJ...868...71S

We present a spectral-timing analysis of observations taken in fall 2017 of the newly detected X-ray transient MAXI J1535-571. We included 38 Swift/XRT window timing mode observations, 3 XMM-Newton observations, and 31 Neutron star Interior Composition Explorer observations in our study. We computed the fundamental diagrams commonly used to study black hole transients, and fitted power density and energy spectra to study the evolution of spectral and timing parameters. The observed properties are consistent with a bright black hole X-ray binary (F_0.6–10keV^{max}^=3.71±0.02×10^–7 erg cm^–2 s^–1) that evolves from the low-hard-state to the high-soft state and back to the low-hard-state. In some observations the power density spectra showed type-C quasiperiodic oscillations, giving additional evidence that MAXI J1535-571 is in a hard state during these observations. The duration of the soft state with less than 10 days is unusually short and observations taken in spring 2018 show that MAXI J1535-571 entered a second (and longer) soft state.