The dust reverberation mapping is one of powerful methods to investigate the structure of the dusty tori in AGNs , and it has been performed on more than a hundred type 1 AGNs .
However , no clear results have been reported on type 2 AGNs because their strong optical–UV extinction completely hides their accretion disc emission .
Here we focus on an X-ray-bright type 2 AGN , NGC 2110 , and utilize 2–20 keV X-ray variation monitored by MAXI to trace disc emission , instead of optical–UV variation .
Comparing it with light curves in the WISE infrared ( IR ) W1 band ( \lambda = 3.4 ~ { } \mu m ) and W2 band ( \lambda = 4.6 ~ { } \mu m ) with cross-correlation analyses , we found candidates of the dust reverberation time lag at \sim 60 days , \sim 130 days , and \sim 1250 days between the X-ray flux variation and those of the IR bands .
By examining the best-fitting X-ray and IR light curves with the derived time lags , we found that the time lag of \sim 130 days is most favoured .
With this time lag , the relation between the time lag and luminosity of NGC 2110 is consistent with those in type 1 AGNs , suggesting that the dust reverberation in NGC 2110 mainly originates in hot dust in the torus innermost region , the same as in type 1 AGNs .
As demonstrated by the present study , X-ray and IR simultaneous monitoring can be a promising tool to perform the dust reverberation mapping on type 2 AGNs .