# The Variability and Period Analysis for the BL Lac AO 0235+164

## TL;DR

This study presents optical and radio variability analysis of BL Lac AO 0235+164, revealing significant brightness changes and a time lag between optical and radio emissions, enhancing understanding of its emission mechanisms.

## Contribution

It provides new optical R-band observations and correlates optical and radio variability, identifying a time lag that informs models of emission regions in BL Lac objects.

## Key findings

- Optical brightness varied by 4.88 mag with rapid changes.
- Optical variations lead radio by approximately 23 days.
- Detected significant short-term variability in optical data.

## Abstract

Variability is one of the extreme observational properties of BL Lacertae objects. AO 0235+164 is a well studied BL Lac through the whole electro-magnetic wavebands. In the present work, we show its optical R band photometric observations carried out during the period of Nov, 2006 to Dec. 2012 using the Ap6E CCD camera attached to the primary focus of the $\rm 70-cm$ meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of $\Delta R$ = 4.88 mag (14.19 - 19.07 mag) and a short time scale of $\Delta T_v$ = 73.5 min during our monitoring period. During the period of Dec. 2006 to Nov. 2009, we made radio observations of the source using the 25-m radio telescope at Xinjiang Astronomical Observatory. When a discrete correlation function (DCF) is adopted to the optical and radio observations, we found that the optical variation leads the radio variation by 23.2$\pm$12.9 days.