Characterization of the Colliding Wind Region in the Superluminous Massive η Carinae

The massive binary system, η Car, is a Colliding Wind Binary with strong stellar winds that can reach hypersonic velocities up to 3000 km/s. With a high eccentricity of 0.9 and a period of 5.53 years the binary system passed periastron in February 2020. When the strong winds from the Luminous Blue Variable component (η Car A) collide with the wind from a mysterious companion (η Car B), a hot Colliding Wind Region (CWR) produces X-rays between 0.1 - 10.0- keV showing strong emission lines from Ions of elements like Fe, Ca, Mg, Si, and S. We present a new detailed X-ray line identification, with the analysis of the profiles and their changes over time using 20 years of observations made by the Chandra X-ray Observatory to characterize the physics of the CWR. We include in our analysis new Chandra observations made in 2019 and 2020 to study the sudden drop in η Car's X-ray emission and recovery. Our new Chandra X-ray observations are compared with X-ray monitoring observations by the NICER X-ray telescope installed at the ISS. Combining 28 HETG Chandra observations I produce a spectrum with ~1.9 Msec to make the most complete line identification of η Car to date. The S/N of the combined spectrum it is so high that "special" spectral features observed in the past are clearly observed allowing us to make a more detailed analysis. I analyze line profiles of strong lines Fe XXV, Fe XXVI, S XVI, S XV, Si XIV, Si XIII, and Mg XII measuring line centroids and widths to provide information of kinematics and dynamics in η Car's colliding wind. The Chandra observations are contrasted with X-ray monitoring programs made by RXTE and Swift. I also present frequent monitoring by NICER of the X-ray spectra from 0.5-10 keV through NICER's observatory science period and the approved monitoring programs obtained in Cycle 1, Cycle 2, and Cycle 3. We use NICER spectra to measure variations in column density, temperatures, emission, and flux from η Car and compare them with observations made by other X-ray telescopes. We find evidence, for the first time, of a decrease in the colliding wind temperatures just before the X-ray emission starts to decline. I compare colliding-wind binary hydrodynamical model predictions to the NICER observations. We also observed the shortest X-ray recovery of η Car.