Program: GN-2017A-Q-41

The most promising technique to constrain the location and geometry of the dusty torus is reverberation, i.e. measuring the time with which the dust responds to changes in the ionising flux. Here we propose the first spectroscopic monitoring campaign of the dusty torus in a luminous, local AGN. Our case study will be Mrk 876 (z=0.129). Near-IR spectroscopy, unlike photometry, can explore several signatures of the hottest dust simultaneously, and it is through their combination that will constrain its location, geometry and chemistry. We will determine: (i) how the hot dust spectral energy distribution (i.e. both temperature and flux) changes in response to the variable ionising continuum, (ii) the dust reverberation lag time at several near-IR frequencies, (iii) the variability of the Paschen broad emission lines, and (iv) the variability of the strongest near-IR coronal lines. Mrk 876 has en estimated dust response time of about a year, broad emission lines with the broad- and narrow-line components clearly discernible and strong coronal lines. We have already started our near-IR monitoring campaign with GNIRS in semester 2016A and wish to continue it in this semester. Our program is supported by an extensive optical monitoring campaign with the 2 m LCOGT.