Revealing the Warm Absorber in MCG--6-30-15 with the Chandra HETG

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  • 4 January 2001
Abstract
We present detailed evidence for a warm absorber in the Seyfert 1 galaxy MCG--6-30-15 and refute earlier claims for relativistic O line emission. The HETG spectra show numerous absorption lines from a wide range of ionization states of N, O, Mg, Ne, Si, S, Ar, Ca and Fe. The O VII edge and 1s^2--1snp resonance line series to n=9 are clearly detected at rest in the AGN frame. We attribute previous reports of an apparently highly redshifted O VII edge to the 1s^2--1snp (n > 5) O VII resonance lines, and a neutral Fe L absorption complex. The shape of the Fe L feature is nearly identical to that seen in the spectra of several X-ray binaries and gives the first direct X-ray evidence for dust embedded in a warm absorber. The O VIII resonance lines and weak edge are also detected, and the spectral rollover below ~ 2 keV is explained by the superposition of numerous absorption lines and edges. We identify, for the first time, a KLL resonance in the O VI photoabsorption cross section, giving a measure of the O VI column density. The O VII (f) emission detected at the systemic velocity implies an ~5% covering fraction and no major changes in average source flux over the past century. Our observations show that a warm absorber model is not only adequate for MCG--6-30-15, the data REQUIRE it. This contradicts the conclusions of Branduardi-Raymont et al. (2001) and eliminates the arguments in favor of low energy, highly relativistic line emission from the vicinity of the black hole (the relativistic 6 keV Fe line is not in question).

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