Unraveling the enigmatic soft x-ray excess: Current understanding and future perspectives

This article explores various theoretical models proposed to explain the soft x-ray excess phenomenon, including warm Comptonization, ionized reflection models, and ionized outflowing disc winds. The soft x-ray excess is better understood thanks to crucial observations made by ROSAT, XMM-Newton, and eROSITA. The article briefly touches upon historical discoveries in this field, specifically the initial detection of the soft x-ray excess in Narrow Line Seyfert 1 galaxies. While progress has been made in comprehending the soft x-ray excess, the article also acknowledges the challenges and limitations of the different models. We emphasize the importance of further studies to refine theoretical models by, for example, building up a large database of reverberation time lags between the disc and coronal x-ray emission to achieve a more comprehensive understanding of this intriguing phenomenon.