LST-1 observations of an enormous flare of BL Lacertae in 2021

TL;DR

LST-1, a prototype Cherenkov telescope, observed a major gamma-ray flare from BL Lacertae in 2021, detecting rapid intra-night variability and contributing valuable data on blazar activity at tens of GeV energies.

Contribution

This work presents the first detailed analysis of BL Lacertae flares observed by LST-1, demonstrating its capability to detect rapid variability at low gamma-ray energies.

Findings

Detection of significant gamma-ray flares from BL Lac in 2021

Observation of intra-night variability reaching 3-4 times the Crab Nebula flux

LST-1's successful operation in capturing rapid flux changes

Abstract

The first prototype of LST (LST-1) for the Cherenkov Telescope Array has been in commissioning phase since 2018 and already started scientific observations with the low energy threshold around a few tens of GeV. In 2021, LST-1 observed BL Lac following the alerts based on multi-wavelength observations and detected prominent gamma-ray flares. In addition to the daily flux variability, LST-1 also detected sub-hour-scale intra-night variability reaching 3-4 times higher than the gamma-ray flux from the Crab Nebula above 100 GeV. In this proceeding, we will report the analysis results of LST-1 observations of BL Lac in 2021, especially focusing on flux variability.