Origin of the Fe K line in the NuSTAR spectrum near Sgr A*

Ascertain whether the Fe K emission line observed in the NuSTAR spectrum during the April 5, 2024 observation originates from Sgr A* or from the nearby supernova remnant Sgr A East, given the inability to spatially disentangle these sources at NuSTAR’s 43-arcsecond resolution.

Background

During the NuSTAR observations coincident with JWST monitoring, the authors detected a clear Fe K line in the X-ray spectrum. Due to NuSTAR's spatial resolution and the proximity of Sgr A East to Sgr A*, the origin of the line cannot be distinguished from the blended field.

Although the flare spectrum could be studied by treating the non-flare emission as background, identifying the source of the Fe K line is important for interpreting the composition of the non-flare X-ray emission and its relation to the environment around Sgr A*. This uncertainty affects models of the quiescent and flaring emission components.

References

An Fe K line is clearly visible, but it is unclear whether this originates from Sgr A* or from the Sgr A East SNR, which cannot be disentangled from Sgr A* at the spatial resolution of NuSTAR (43'').

— Simultaneous JWST, NuSTAR, and VLA Monitoring of Sgr A*: A Unified Picture of the Variable IR, X-ray and Radio Emission  (2512.20786 - Yusef-Zadeh et al., 23 Dec 2025) in Section 3.2 (NuSTAR X-ray data reduction)