2025ApJ...982...25D

In active galactic nuclei, X-ray illumination of the accretion disk around a supermassive black hole (SMBH) results in the production of the Kα fluorescent line of iron, which provides insights into accretion physics and SMBH spins. In this work, we studied X-ray reflection from the accretion disk in the Seyfert 1 galaxy NGC 3783 using all the data collected by the Chandra High Energy Transmission Grating Spectrometer. We used hardness-ratio diagrams to distinguish between different spectral states and conducted spectral analysis of all the multiepoch data sets, as well as the source in the observed spectral states. Our hardness analysis indicates that the source gradually evolved into a harder state (2013-2016) compared to the previous epochs (2000-2001). Our spectral modeling implies that the relativistically broadened iron emission from the innermost accretion disk is associated with a near-maximal SMBH spin ($a=0.9{8}_{-0.12}^{+0.02}$) in all the data sets, even though the hard state was present in 17% of them, and a consistent spin is also found in different spectral states. In addition, the narrow, bright Fe Kα line from distant regions has an excess velocity of $62{0}_{-70}^{+80}$ km s^–1 relative to the rest frame, implying that some distant layers of the disk could be twisted. Our results suggest that, despite long-term changes in the X-ray brightness of NGC 3783, likely caused by eclipsing material, the relativistic reflection can be constrained thanks to the substantial counts provided by the multiepoch observations, while a warped disk structure may be present.