Improving the Flux Calibration in Reverberation Mapping by Spectral Fitting:Application to the Seyfert Galaxy MCG-6-30-15

Abstract

We propose a method for the flux calibration of reverberation mapping spectra, based on accurate measurement of [O III] λ5007 emission by spectral fitting. Our method can achieve better accuracy than the traditional method of Groningen & Wanders, allowing reverberation mapping measurements for objects with variability amplitudes as low as ∼5%. As a demonstration, we reanalyze the data of the Seyfert 1 galaxy MCG-6-30-15, taken from the 2008 campaign of the Lick active galactic nucleus monitoring project, which previously failed to obtain a time lag for this weakly variable object, owing to a relatively large flux calibration uncertainty. We detect a statistically significant rest-frame time lag of {6.38}_-2.69^+3.07 days between the Hβ and V-band light curves. Combining this lag with FWHM(Hβ) = 1933 ± 81 km s^-1 and a virial coefficient of f = 0.7, we derive a virial black hole mass of {3.26}_-1.40^+1.59× {10}⁶ M _⊙, which agrees well with previous estimates by other methods.