The Soft State of the Black Hole Transient Source MAXI J1820+070: Emission from the Edge of the Plunge Region?

Understand

The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the Sky.

• It was too bright for X-ray CCD instruments such as XMM-Newton and Chandra, but was well observed by photon-counting instruments such as NICER and NuSTAR.
• We report here on the discovery of an excess emission component during the soft state.
• It is best modelled with a blackbody spectrum in addition to the regular disk emission, modelled either as diskbb or kerrbb.