Ultraluminous X-ray Sources in the Interacting Galaxy System NGC4490 and NGC4485

We report the X-ray study of five brightest ultraluminous X-ray sources (ULXs) in the interacting galaxy system NGC4490 and NGC4485 using the archived data from three Chandra and one XMMNewton 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.
Meeting Information: The 3rd Suzaku international Conference "Energetic Cosmos : from Suzaku to ASTRO-H" (June 29-July 2, 2009. Grand Park Otaru Hotel), Otaru, Hokkaido Japan
Meeting sponsors: The University of Tokyo, The Institute of Physical and Chemical Research, The Japan Society for the Promotion of Science