A New Phase of Optical Activity of BL Lacertae in the Fall of 2024: Intra-Night Flux and Polarization Variations

TL;DR

This study documents unprecedented intra-night optical flux and polarization variability in BL Lacertae during fall 2024, providing insights into jet emission mechanisms through high-resolution, multi-band observations.

Contribution

It presents the most rapid intra-night variability episodes in a blazar with detailed polarization and flux analysis, enhancing understanding of jet physics.

Findings

Confirmed zero time delay between optical bands at minute scale.

Observed stable polarization during rapid flux variations.

Detected some of the most spectacular intra-night variability episodes.

Abstract

BL Lacertae is not only archetypical of an entire class of jet-dominated active galactic nuclei, blazars, but also one of the most active and rapidly changing objects in this class. In the fall of 2024 (September--November), BL Lacertae underwent another episode of strong optical activity, reaching an R-band magnitude of about 12 and showing extremely rapid and large-amplitude inter- and intra-night flux and polarization variations. During this period, the object was monitored over 40 nights using telescopes with an aperture of up to 2 m at three observatories: Rozhen and Belogradchik in Bulgaria and Skinakas in Greece. The results from this study include some of the most spectacular intra-night variability episodes detected in a blazar. These rapid variations, combined with high photometric accuracy and high time resolution, allowed for confirmation of consistency between different optical bands with zero time delays, down to a minute scale. Unlike previous activity reports, polarization was relatively stable on these short time-scales. Possible connections between polarization, flux, and intra-night variability were explored in order to better model or constrain the physical processes and emission mechanisms in the relativistic jets.