# Time delay measurement of Mg II line in CTS C30.10 with SALT

## TL;DR

This study presents a 6-year monitoring of the quasar CTS C30.10, measuring the Mg II emission line time delay to understand the broad-line region size and its relation to luminosity, using SALT observations and multiple analysis methods.

## Contribution

First measurement of Mg II line time delay in a distant quasar using SALT, confirming the radius-luminosity relation similar to Hβ line studies.

## Key findings

- Mg II line time delay is approximately 562-564 days.
- The radius-luminosity relation for Mg II is consistent with that of Hβ.
- The results support the use of Mg II for black hole mass estimates at high redshift.

## Abstract

We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope (SALT). We measured the rest-frame time-lag of $562\pm 2$ days between the continuum variations and the response of the Mg II emission line, using the Javelin approach. More conservative approach, based on five different methods, imply the time delay of $564^{+109}_{-71}$ days. This time delay, combined with other available measurements of Mg II line delay, mostly for lower redshift sources, shows that the Mg II line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied H$\beta$ line.