Quasar X-ray Classification: Bright vs. Weak

Quasars are extremely luminous active galactic nuclei that emit large amounts of energy across the electromagnetic spectrum, including X-rays. X-ray bright and X-ray weak quasars can be distinguished based on their X-ray emission levels.

1. 'X-ray Bright Quasars': 'X-ray bright quasars' refer to those quasars that emit a significant amount of X-ray radiation. These quasars have high X-ray luminosities and can be easily detected in X-ray surveys. They typically exhibit strong X-ray emission lines and have a high X-ray-to-optical flux ratio.

2. 'X-ray Weak Quasars': 'X-ray weak quasars', on the other hand, emit relatively low levels of X-ray radiation. They have lower X-ray luminosities compared to 'X-ray bright quasars' and may be more challenging to detect in X-ray surveys. 'X-ray weak quasars' often have weaker or even undetectable X-ray emission lines and a lower X-ray-to-optical flux ratio.

The distinction between 'X-ray bright' and 'X-ray weak' quasars is primarily based on the strength of their X-ray emission and the resulting X-ray luminosity. However, it is important to note that these classifications may also depend on the sensitivity of the X-ray observatory used for the observations and the specific detection thresholds employed.