We present the first results from a detailed analysis of photometric and spectrophotometric data on the narrow-line Seyfert 1 galaxy Mrk 335 , collected over a 120-day span in the fall of 2010 .
From these data we measure the lag in the He ii \lambda 4686 broad emission line relative to the optical continuum to be 2.7 \pm 0.6 days and the lag in the H \beta \lambda 4861 broad emission line to be 13.9 \pm 0.9 days .
Combined with the line width , the He ii lag yields a black hole mass , M _ { BH } = ( 2.6 \pm 0.8 ) \times 10 ^ { 7 } M _ { \odot } .
This measurement is consistent with measurements made using the H \beta \lambda 4861 line , suggesting that the He ii emission originates in the same structure as H \beta , but at a much smaller radius .
This constitutes the first robust lag measurement for a high-ionization line in a narrow-line Seyfert 1 galaxy and supports a scenario in which the He ii emission originates from gas in virial motion rather than outflow .