The broad-line region and dust torus size of the Seyfert 1 galaxy PGC 50427

Abstract

We present the results of three-year monitoring campaigns of the z = 0.024 type 1 active Galactic nucleus (AGN) PGC 50427. Using robotic telescopes of the Universitatssternwarte Bochum near Cerro Armazones in Chile, we monitored PGC 50427 in the optical and near-infrared (NIR). Through the use of photometric reverberation mapping with broad-and narrow band filters, we determine the size of the broad-line emitting region by measuring the time delay between the variability of the continuum and the Ha emission line. The Ha emission line responds to blue continuum variations with an average rest frame lag of 19.0 +/- 1.23 days. Using single epoch spectroscopy obtained with the Southern African Large Telescope (SALT) we determined a broad-line H alpha velocity width of 1020 km s(-1) and in combination with the rest frame lag and adoption of a geometric scaling factor f = 5.5, we calculate a black hole mass of M-BH similar to 17 x 10(6) M-circle dot. Using the flux variation gradient method, we separate the host galaxy contribution from that of the AGN to calculate the rest frame 5100 angstrom luminosity at the time of our monitoring campaign. We measured small luminosity variations in the AGN (similar to 10%) accross the three years of the monitoring campaign. The rest frame lag and the host-subtracted luminosity permit us to derive the position of PGC 50427 in the BLR size - AGN luminosity diagram, which is remarkably close to the theoretically expected relation of R proportional to L-0.5. The simultaneous optical and NIR (J and K-s) observations allow us to determine the size of the dust torus through the use of dust reverberation mapping method. We find that the hot dust emission (similar to 1800 K) lags the optical variations with an average rest frame lag of 46.2 +/- 2.60 days. The dust reverberation radius and the nuclear NIR luminosity permit us to derive the position of PGC 50427 on the known tau - MV diagram. The simultaneous observations for the broad-line region and dust thermal emission demonstrate that the innermost dust torus is located outside the BLR in PGC50427, supporting the unified scheme for AGNs.