X-ray, Optical, and Near-infrared Monitoring of the New X-ray Transient MAXI J1820+070 in the Low/hard State

Understand

We report X-ray, optical, and near-infrared monitoring of the new X-ray transient MAXI J1820$+$070 discovered with MAXI on 2018 March 11.

• Its X-ray intensity reached $\sim 2$ Crab in 2--20 keV at the end of March, and then gradually decreased until the middle of June.
• In this period, the X-ray spectrum was described by Comptonization of the disk emission, with a photon index of $\sim$1.5 and an electron temperature of $\sim$50 keV, which is consistent with a black hole X-ray binary in the low/hard state.
• The electron temperature and the photon index were slightly decreased and increased with increasing flux, respectively.