Photometric AGN reverberation mapping – an efficient tool for BLR sizes, black hole masses, and host-subtracted AGN luminosities

Abstract

Photometric reverberation mapping employs a wide band pass to measure the AGN continuum variations and a suitable narrow band to trace the echo of an emission line in the broad line region (BLR). The narrow band catches both the emission line and the underlying continuum, and one needs to extract the pure emission line light curve. We performed a test on two local AGNs, PG0003+199 and Ark120, by observing well-sampled broad-(B, V) and narrow-band light curves with the robotic 15 cm telescope VYSOS-6 on Cerro Armazones, Chile. We find that, as long as the emission line contributes 50% to the band pass, the pure emission line light curve can be reconstructed from photometric monitoring data so that the time lag τ can be measured. For both objects the lags are consistent with spectroscopic reverberation results. We calculated virial black hole masses in agreement with literature values, by combining the BLR size R BLR (τ) from photometric monitoring with the velocity dispersion of a single contemporaneous spectrum. Applying the flux variation gradient method, we estimate the host galaxy contribution in the apertures used and the host-subtracted restframe 5100 Å luminosity L AGN . Our L AGN differs significantly from previous estimates, placing both sources ∼50% closer to the R BLR − L AGN relation. This suggests that the scatter in the current R BLR − L AGN relation is largely caused by uncertainties in R BLR due to undersampled light curves and by uncertainties in the host-subtracted AGN luminosities inferred so far. If the scatter can be reduced, then two quasar samples matching in R BLR should also match in intrinsic L AGN , independent of redshift, thus offering the prospect of probing cosmological models. Photometric reverberation mapping opens the door to efficiently measuring hundreds of BLR sizes and host-subtracted AGN luminosities even with small telescopes, but also routinely with upcoming large survey telescopes like the LSST.

Imprints of the quasar structure in time-delay light curves: Microlensing-aided reverberation mapping

“…The proposed technique of microlensing-aided reverberation mapping aims at taking advantage of this effect to measure the time lag between the continuum and broad line variations. Our method is not conceptually very different from photometric reverberation mapping (Haas et al 2011;Chelouche & Daniel 2012;Chelouche & Zucker 2013;Pozo Nuñez et al 2012;Edri et al 2012;Zu et al 2014;Bachev et al 2014). In that case, multi-band photometry is used to disentangle the flux of the continuum and of the BLR, while our technique can already be applied to singleband data.…”

Size and disk-like shape of the broad-line region of ESO 399-IG20

“…Recently, Haas et al (2011) proposed photometric reverberation mapping (PRM) as an efficient method to determine the BLR size through the use of broad band filters to trace the AGN continuum variations and narrow-band filters to catch the BLR emission line response. Because the narrow-band collects both the emission line flux and the underlying continuum, the challenge is to extract the pure emission line light curve.…”

“…While this method does not place a strict requirement on the object's redshift such that the emission line falls into the narrow-band filter (as in the case proposed by Haas et al 2011), the use of broad band filters only (as proposed by limits the application of PRM to cases with a sufficiently strong emission line contribution in the respective filter used. Despite of this handicap, this method has been successfully applied to determine the BLR size for one lowluminosity AGN NGC 4395 (Edri et al 2012) and one high-z luminous MACHO quasar ) consistent with previous spectroscopic RM results.…”

“…An advantage is that it does not require high spatial resolution imaging and can be applied directly to the monitoring data. Recently, FVG has been tested on PRM data (Haas et al 2011;Pozo Nuñez et al 2012). These tests show that by using a well defined range for the host galaxy slope (Sakata et al 2010) it is possible to separate the AGN contribution at the time of the monitoring campaigns.…”

“…Both results allow us to infer its position in the BLR sizeLuminosity R BLR ∝ L 0.5 AGN diagram. Additionally, pure broadband PRM ) is applied and compared with the broad-and narrow-band PRM technique (Haas et al 2011). Finally, the geometry of the BLR, whether spherical or an inclined disk, is inferred via light curve modeling.…”