ISS/NICER X-ray observations of eta Car

The system is highly eccentric (e~0.9), resulting in modulated X-ray emission during its 5.54yr orbit. The X-ray flux increases in the months prior to periastron passage, exhibiting strong flares, then rapidly declines to a flat minimum lasting a few weeks, followed by a gradual recovery.

We present the Neutron Star Interior Composition Explorer telescope spectra obtained before, during, and after the 2020 X-ray minimum, and perform spectral analysis to establish the temporal behavior of the X-ray flux and X-ray-absorbing column density (N_H_(t)) for the 2-10keV and 5-10keV energy ranges. The latter range is dominated by the stellar wind-collision region and, therefore, these spectral parameters-in particular, N_H_(t)-serve as potentially stringent constraints on the binary orientation.