Direct spectroscopic observation of matter falling onto a compact stellar object.

Abstract

GX 301-2 is an accreting x-ray pulsar with a massive hypergiant companion WRAY 977, embedded within a dense circumstellar environment. We report on detected redshifted hydrogen- and helium-like iron lines, together with transitions from lower ionization states, observed with XRISM/Resolve during an x-ray flare. Notably, these spectral features evolve from absorption lines at the beginning of the observation to emission lines at the end, with intervening phases exhibiting a mixture of both absorption and emission features. This behavior constitutes direct evidence of inflowing material accreting onto the neutron star. The results suggest a dynamic accretion geometry, evolving from predominantly radial inflow to a transverse, potentially disk-like configuration during the x-ray flare. Observations of inflowing matter thus constitute a direct test of accretion hypotheses and highlight the complex interplay between stellar wind and transient accretion disks in wind-accreting systems.