Presentation #114.05 in the session Stellar-Mass and Galactic Black Holes.
Astrophysical black holes tell us about accretion and ejection physics in the strongest gravity regime in the Universe. Reverberation mapping is a tool for “resolving” those compact regions, in which X-ray light echoes off the accretion disk near the innermost stable circular orbit. The NICER Observatory has revolutionized reverberation mapping the inner accretion disks of black hole X-ray binaries in outburst, and in this talk, I will give an overview of these recent results. In particular, I will present our key finding that the reverberation lags get longer during the hard-to-soft state transition when a ballistic radio jet is launched. This may suggest an increase in the size of the X-ray emitting region, possibly due to an expanding corona. I will present the modeling results using the reverberation model reltrans for MAXI J1820+070 and MAXI J1535-571, and put these results into the context of other multi-wavelength approaches to understanding the disk-corona-jet connection in black hole transients.