Spectroscopic reverberation mapping of Quasar PKS 0736 + 017: broad-line region and black-hole mass

Abstract

To understand the mass distribution and co-evolution of supermassive black holes with their host galaxy, it is crucial to measure the black hole mass of AGN. Reverberation mapping is a unique tool to estimate the black hole masses in AGN. We performed spectroscopic reverberation study using long-term monitoring data with more than 100 spectra of a radio-loud quasar PKS 0736 + 017 to estimate the size of the broad-line region (BLR) and black hole mass. The optical spectrum shows strong H β and H γ emission lines. We generated the light curves of 5100 Å continuum flux (f5100), H β, and H γ. All the light curves are found to be strongly variable with fractional variability of 69 per cent, 21 per cent, 30 per cent for V-band, H β, and H γ light curves, respectively. Along with the thermal contribution, non-thermal emission contributes to the estimated continuum luminosity at 5100 Å. Using different methods, e.g. CCF, JAVELIN, von-neumann, we estimated the size of the BLR, which is found to be 66.4+6.0−4.2−4.2+6.0 light days in the rest frame. The BLR size combined with the line width of H β provides a black hole mass of 7.32+0.89−0.91×107M⊙−0.91+0.89×107M⊙⁠. The source closely follows the BLR size–luminosity relation of AGN.