摘要
Distinct changes of the spectral and variability properties observed in black hole transients during a bright outburst deliver insight into the evolution of the accretion flow and accretion geometry. We investigated NICER and Swift monitoring observations of H 1743-322 during its 2018 outburst as well as NuSTAR and XMM-Newton data. The observed hardness ratios, rms amplitudes, and properties of quasiperiodic oscillations indicate that H 1743-322 showed another hard-state-only, or so-called "failed", outburst. The energy spectra obtained from NuSTAR and XMM-Newton data confirm the hard-state nature and give photon indices of ∼1.7, typically found in the hard state of H 1743-322. The NICER monitoring observations allow us to follow the evolution of covariance ratios during a hard-state-only outburst of H 1743-322 for the first time. We confirm that the presence of flat covariance ratios at low energies is established early in the outburst and find that this shape is maintained throughout the outburst.