Asca Observation of an X-ray–luminous Active Nucleus in Markarian

We have obtained a moderately long (10 s) ASCA observation of the Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous infrared galaxy population. In the best-fitting model we do not see the X-ray source directly; the spectrum consists of a scattered power-law component and a reflection component, both of which have been absorbed by a column . About three-quarters of the observed hard 22 22 N ≈ 3 # 10 cm H X-rays arise from the scattered component, reducing the equivalent width of the iron Ka line. The implied ratio of 1–10 keV X-ray luminosity to bolometric luminosity, , is typical of Seyfert 1 galaxies and radioL /L ∼ 2% X bol quiet QSOs of comparable bolometric luminosities and indicates that the bolometric luminosity is dominated by the active galactic nucleus (AGN). Our estimate of the X-ray luminosity also moves Mrk 231 in line with the correlations found for AGNs with extremely strong Fe ii emission. A second source separated by about 29 is also clearly detected and contributes about 25% of the total flux. Subject headings: galaxies: active — galaxies: individual (Markarian 231) — galaxies: nuclei — galaxies: Seyfert — X-rays: galaxies