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Stellar magnetic activity provides substantial information on the magneticdynamo and the coronal heating process. We present a catalog of X-ray activityfor about 6000 stars, based on the $Chandra$ and $Gaia$ DR2 data. We alsoclassified more than 3000 stars as young stellar objects, dwarf stars, or giantstars. By using the stars with valid stellar parameters and classifications, westudied the distribution of X-ray luminosity ($L_X$) and the ratio ofX-ray-to-bolometric luminosities ($R_X$), the positive relation between $L_X$,$R_X$, and hardness ratio, and the long-term X-ray variation. This catalog canbe used to investigate some important scientific topics, including theactivity-rotation relation, the comparison between different activityindicators, and the activities of interesting objects (e.g., A-type stars andgiants). As an example, we use the catalog to study the activity-rotationrelation, and find that the young stellar objects, dwarfs, and giants fall on asingle sequence in the relation $R_X$ versus Rossby number, while the giants donot follow the relation $R_X$ versus $P_{\rm rot}^{-2}R^{-4}$ valid for dwarfs.

Stellar X-ray activity across the Hertzsprung-Russell diagram. I. Catalogs