Optical monitoring of the broad-line radio galaxy 3C390.3

Matthias Dietrich, Bradley M. Peterson, Catherine J. Grier, Misty C. Bentz, Jason Eastman, Stephan Frank, Raymond Gonzalez, Jennifer L. Marshall, Darren L. Depoy, Jose L. Prieto

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


We have undertaken a new ground-based monitoring campaign on the broad-line radio galaxy 3C390.3 to improve the measurement of the size of the broad emission-line region and to estimate the black hole mass. Optical spectra and g-band images were observed in late 2005 for three months using the 2.4m telescope at MDM Observatory. Integrated emission-line flux variations were measured for the hydrogen Balmer lines Hα, Hβ, Hγ, and for the helium line He IIλ4686, as well as g-band fluxes and the optical active galactic nucleus (AGN) continuum at λ =5100 Å. The g-band fluxes and the optical AGN continuum vary simultaneously within the uncertainties, τcent = (0.2 ± 1.1)days. We find that the emission-line variations are delayed with respect to the variable g-band continuum by τ(Hα) = 56.3+2.4-6.6days, τ(Hβ) = 44.3+3.0-3.3days, τ(Hγ) = 58.1 +4.3-6.1days, and τ(He II4686) = 22.3 +6.5-3.8days. The blue and red peaks in the double-peaked line profiles, as well as the blue and red outer profile wings, vary simultaneously within ±3 days. This provides strong support for gravitationally bound orbital motion of the dominant part of the line-emitting gas. Combining the time delay of the strong Balmer emission lines of Hα and Hβ and the separation of the blue and red peaks in the broad double-peaked profiles in their rms spectra, we determine Mvir bh = 1.77+0.29-0.31 × 108 MȮ and using σline of the rms spectra M vir bh = 2.60+0.23-0.31 × 108 MȮ for the central black hole of 3C390.3, respectively. Using the inclination angle of the line-emitting region which is measured from superluminal motion detected in the radio range, accretion disk models to fit the optical double-peaked emission-line profiles, and X-ray observations, the mass of the black hole amounts to Mbh = 0.86 +0.19-0.18 × 109 MȮ (peak separation) and Mbh = 1.26+0.21-0.16 × 109 MȮline), respectively. This result is consistent with the black hole masses indicated by simple accretion disk models to describe the observed double-peaked profiles, derived from the stellar dynamics of 3C390.3, and with the AGN radius-luminosity relation. Thus, 3C390.3 as a radio-loud AGN with a low Eddington ratio, L edd/L bol = 0.02, follows the same AGN radius-luminosity relation as radio-quiet AGNs.

Original languageEnglish (US)
Article number53
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 20 2012
Externally publishedYes


  • galaxies: active
  • quasars: emission lines
  • quasars: individual (3C390.3)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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