Direct observation of the Broad Line Region in X-rays during the low state of NGC4051

Abstract

NGC 4051 is one of the X-ray brightest and most variable Seyfert galaxies. During 2009 NGC 4051 was caught at its lowest state ever observed by $XMM-Newton$. The low source continuum emission allows a clear measurement of the He-like emission lines of N${}^{+5}$ and O${}^{+6}$. The exceptionally high intercombination line flux is a direct measurement of either a high density or a UV irradiated photoionized plasma. Either way, this provides an unambiguous distance diagnostic. We find that the line emitting region has a density of $\sim 3\times 10^{10}$ cm${}^{-3}$ and distance of a few $10^{15}$ cm from the continuum source, placing it within the UV-optical Broad Line Region of NGC 4051. Both N${}^{+5}$ and O${}^{+6}$ independently result in similar measurements for density and distance. In addition, we find the kinematics of the broad O${}^{+7}$ Ly$\alpha$ match those of the He${}^{+1}\lambda 4686$\,Å line, which is associated with the NGC 4051 Broad Line Region. This is the first direct X-ray measurement of a Seyfert Broad Line Region.

References in corpus (11)

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Cited by in corpus (5)

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• A systematic study of photoionized emission and warm absorption signatures of the NLS1 Mrk 335
• Variable oxygen emission from the accretion disk of Mrk 110
• Study of the optical to X-ray broad emission lines of Mrk 110
• A NICER viewing angle on the accretion stream of Vela X-1