CHANDRA OBSERVATIONS OF NGC 4698: A SEYFERT 2 GALAXY WITH NO ABSORPTION

摘要

We present Chandra ACIS-S observations of the enigmatic Seyfert 2 galaxy NGC 4698. This object, together with several other bona fide Seyfert 2 galaxies, shows no absorption in the low spatial resolution ASCA data, in contrast to the standard unification models. Our Chandra observations of NGC 4698 probe directly the nucleus, allowing us to check whether nearby sources contaminate the ASCA spectrum. Indeed, the Chandra observations show that the ASCA spectrum is dominated by two nearby AGNs. The X-ray flux of NGC 4698 is dominated by a nuclear source with luminosity L_(0.3-8) kev ～ 10~(39) ergs s~(-1), coincident with the radio nucleus. Its spectrum is well represented by a power law, Γ ≈ 2.2, obscured by a small column density of 5 x 10~(20) cm~(-2), suggesting that NGC 4698 is an atypical Seyfert galaxy. On the basis of its low luminosity, we then interpret NGC 4698 as a Seyfert galaxy that lacks a broad-line region.