The Relative Wavelength Independence of IR Time Lags in NGC4151 During
  the Years 2010-2015
  We present results of a study of the correlation between the infrared (JHKL)
and optical(B) fluxes of the nucleus of the Seyfert galaxy NGC 4151 for the
years 2010 - 2015 using our own data (partially published) in combination with
published data of Roberts and Rumstey (2012), Guo et al. (2014) and Schnulle et
al. (2013, 2015).We find similar lags for each of the HKL passbands relative to
the optical of 37 +-3 days. The lags are the same to within the accuracy of
measurement. We do not confirm a significant decrease in the lag for HKL in
2013-2014 previously reported by Schnulle et al. (2015), but we find that the
lag of the short-lag component of J increased. We discuss our results within
the framework of the standard model, where the variable infrared radiation is
mainly due to the thermal re-emission of short-wave radiation by dust clouds
close to a variable central source. There is also some contribution to the IR
emission from the accretion disk, and this contribution increases with
decreasing wavelength. The variability in J and K is not entirely simultaneous,
which may be due to the differing contributions of the radiation from the
accretion disk in these bands. The absence of strong wavelength-dependent
changes in infrared lag across the HKL passbands can be explained by having the
dust clouds during 2010-2015 be located beyond the sublimation radius. The
relative wavelength independence of the infrared lags is also consistent with
the hollow bi-conical outflow model of Oknyansky et al. (2015).
