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 ] λ 5007 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 days between the H β and V -band light curves. Combining this lag with FWHM(H β ) = 1933 ± 81 km s −1 and a virial coefficient of f  = 0.7, we derive a virial black hole mass of M ⊙ , which agrees well with previous estimates by other methods.