Measurement of The Broad Line Region Size in a Luminous MACHO Quasar

TL;DR

This study measures the size of the broad line region in a luminous high-redshift quasar using broadband photometric reverberation mapping over 7.5 years, finding results consistent with local AGN size-luminosity relations.

Contribution

First application of broadband photometric reverberation mapping to a high-luminosity, high-redshift quasar to estimate BLR size.

Findings

Measured a 180+/-40 day lag in the quasar's emission lines.

Results align with extrapolated local AGN size-luminosity relation.

Supports the use of broadband photometry for high-z quasar BLR studies.

Abstract

We measure the broad emission line region (BLR) size of a luminous, L~1E47 erg/s, high-z quasar using broadband photometric reverberation mapping. To this end, we analyze ~7.5 years of photometric data for MACHO 13.6805.324 (z~1.72) in the B and R MACHO bands and find a time delay of 180+/-40 days in the rest frame of the object. Given the spectral-variability properties of high-z quasars, we associate this lag with the rest-UV iron emission blends. Our findings are consistent with a simple extrapolation of the BLR size-luminosity relation in local active galactic nuclei to the more luminous, high-z quasar population. Long-term spectroscopic monitoring of MACHO 13.6805.324 may be able to directly measure the line-to-continuum time-delay and test our findings.