Multi-color optical monitoring of Mrk 501 from 2010 to 2015

TL;DR

This study presents multi-year optical monitoring of Mrk 501, revealing intraday and long-term variability, a minimal variability timescale of 106 minutes, and a dominant bluer-when-brighter trend supporting the shock-in-jet model.

Contribution

First comprehensive optical variability analysis of Mrk 501 from 2010 to 2015, accounting for host galaxy subtraction and examining color-magnitude behavior.

Findings

Detected intraday variability with a minimum timescale of 106 minutes.

Observed a consistent bluer-when-brighter trend across multiple timescales.

Quantified variability amplitudes and duty cycle for optical bands.

Abstract

We have monitored the BL Lac object Mrk 501 in optical $V$, $R$ and $I$ bands from 2010 to 2015. For Mrk 501, the presence of strong host galaxy component can affect the results of photometry. After subtracting the host galaxy contributions, the source shows intraday and long-term variabilities for optical flux and color indices. The average variability amplitudes of $V$, $R$ and $I$ bands are $22.05\%, 22.25\%, 23.82\%$ respectively, and the value of duty cycle 14.87 per cent. A minimal variability timescale of 106 minutes is detected. No significant time lag between $V$ and $I$ bands is found on one night. The bluer-when-brighter (BWB) trend is dominant for Mrk 501 on intermediate, short and intraday timescales which supports the shock-in-jet model. For the long timescale, Mrk 501 in different state can have different BWB trend. The corresponding results of non-correcting host galaxy contributions are also presented.