Ultraluminous X-ray Sources in the Interacting Galaxy System NGC 4490 and NGC 4485

摘要

We report the X-ray study of five brightest ultraluminous X-ray sources (ULXs) in the interacting galaxy system NGC 4490 and NGC 4485 using the archived data from three Chandra and one XMM-Newton observations. To investigate spectral variations of these ULXs, we plotted their disk luminosities against the innermost disk temperatures estimated via the multi-color disk model. We found that the observed spectral variations are classified into two types; one indicating a power-law relation between the luminosity and the innermost disk temperature and the other without such a relation. The latter type shows flux changes more than an order. We discuss spectral state changes for individual sources.