Horne, Keith, De Rosa, G., Peterson, B. M., Barth, A. J., Ely, J., Fausnaugh, M. M., Kriss, G. A., Pei, L., Bentz, M. C., Cackett, E. M., Edelson, R., Eracleous, M., Goad, M. R., Grier, C. J., Kaastra, J., Kochanek, C. S., Krongold, Y., Mathur, S., Netzer, H., Proga, D., Tejos, N., Vestergaard, M., Villforth, C., Adams, S. M., Anderson, M. D., et al
Abstract
In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity-delay maps for the prominent broad emission lines (Lya, C IV, He II, and Hß) in the spectrum of NGC 5548. These are the most detailed velocity-delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He II response inside 5-10 lt-day has a broad single-peaked velocity profile. The Lya, C IV, and Hß responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s-1 in the 10-20 lt-day delay range. An incomplete ellipse in the velocity-delay plane is evident in Hß. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay $\tau =(R/c)(1-\sin i)\approx 5$ days gives the inclination i ? 45°. The inferred black hole mass is MBH ? 7 × 107 M?. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the "BLR Holiday" identified in previous work. Moreover, a helical "Barber-Pole" pattern, with stripes moving from red to blue across the C IV and Lya line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.
