Decomposition of disk and jet optical emission: Case of PKS~1510-089 and PKS~0736+017

Abstract

Measuring BLR size and black hole mass of jetted quasars with strong radio emission is challenging due to the contribution from non-thermal synchrotron radiation from the jet in the optical continuum. Here, we investigate the optical continuum emission in two flat-spectrum radio quasars (FSRQs), PKS~0736+017 and PKS~1510-089, by separating the thermal emission from the accretion disk and the non-thermal synchrotron emission from the jet using their distinct polarization signatures. Our analysis combines multi-epoch optical spectro-photometric and polarimetric observations from the archival optical continuum, H$β$ emission line light curves from earlier reverberation mapping campaigns, and 37 GHz radio data. For PKS~0736+017, we find that the disk contributes approximately 70 % ($f_d = 0.70^{+0.01}_{-0.01}$) of the total optical emission. After removing the jet component, we obtain a revised H$β$ lag of $84.8^{+23.2}_{-18.4}$ days. In contrast, the disk contribution in PKS~1510-089 is lower with 37.5 % ($f_d = 0.37^{+0.01}_{-0.01}$), with a corresponding H$β$ lag of $54.4^{+4.4}_{-5.4}$ days. Our findings highlight the need for careful decomposition of optical light curves in jet-dominated AGN.