# Multi-color optical monitoring of the quasar 3C 273 from 2005 to 2016

## TL;DR

This study presents a comprehensive 11-year optical monitoring of quasar 3C 273, revealing intraday variability, chromatic trends, and potential quasi-periodicity, contributing valuable long-term data and analysis to quasar variability research.

## Contribution

It provides the first long-term, multi-band optical variability analysis of 3C 273, identifying intraday variability patterns, chromatic trends, and possible periodicity not previously documented.

## Key findings

- Intraday variability detected on seven nights with amplitudes up to 42%.
- A dominant bluer-when-brighter chromatic trend observed at different flux levels.
- Possible quasi-periodicity of approximately 3918 days identified.

## Abstract

We have monitored the quasar 3C 273 in optical $V$, $R$ and $I$ bands from 2005 to 2016. Intraday variability (IDV) is detected on seven nights. The variability amplitudes for most of nights are less than 10\% and four nights more than 20\%. When considering the nights with time spans $>4$ hours, the value of duty cycle (DC) is 14.17 per cent. Over the twelve years, the overall magnitude and color index variabilities are $\bigtriangleup I=0^{\rm m}.67$, $\bigtriangleup R=0^{\rm m}.72$, $\bigtriangleup V=0^{\rm m}.68$, and $\bigtriangleup (V-R)=0^{\rm m}.25$ respectively. The largest clear IDV has an amplitude of 42% over just 5.8 minutes and the weakest detected IDV is 5.4% over 175 minutes. The BWB (bluer when brighter) chromatic trend is dominant for 3C 273 and appears at different flux levels on intraday timescales. The BWB trend exists for short-term timescales and intermediate-term timescales but different timescales have different correlations. There is no BWB trend for our whole time-series data sets. A significant anti-correlation between BWB trend and length of timescales is found. Combining with $V$-band data from previous works, we find a possible quasi-periodicity of $P=3918\pm1112$ days. The possible explanations for the observed variability, BWB chromatic trend and periodicity are discussed.