Abstract

The source BL Lac exhibited an enhanced activity from August 2020 to July 2022. This activity peaked in July–August 2021. In this period the source reached historic brightness maxima in various energy ranges. Observations of this nonstandard maximum were carried out by the SAI staff of the Crimean Station of SAI and with the telescopes of the Caucasus Mountain Observatory (CMO SAI MSU). Optical and near-infrared photometric data as well as optical polarimetric data were obtained. When investigating the correlation between the optical and gamma-ray fluxes and between the optical and infrared fluxes, its high degree with an almost zero lag was confirmed—this means that the emission regions spatially coincide or are very close together. The degree of linear polarization in the investigated period changed in a wide range, reaching 20\({\%}\), with an anticorrelation between the degree of linear polarization and the brightness of the object having been observed. A similar pattern of variation was also observed in the preceding flares of this object. The changes in the electric vector position angle (EVPA) show a dependence on the rate of change of the object’s brightness. The EVPA changed greatly during flares and slowly at the times of a slow change in the intensity.

中文翻译：

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2021 年 7 月至 11 月 BL Lac 火炬燃烧活动调查

摘要

BL Lac 光源在 2020 年 8 月至 2022 年 7 月期间表现出增强的活动。该活动在 2021 年 7 月至 8 月达到顶峰。在此期间，光源在各个能量范围内达到了历史亮度最大值。这一非标准最大值的观测是由 SAI 克里米亚站的 SAI 工作人员使用高加索山天文台 (CMO SAI MSU) 的望远镜进行的。获得了光学和近红外光度数据以及光学偏振数据。在研究光学通量和伽马射线通量之间以及光学通量和红外通量之间的相关性时，证实了其几乎零滞后的高度——这意味着发射区域在空间上重合或非常接近。调查期间线偏振度变化幅度较大，达到20\({\%}\)，线性偏振度与被观察物体的亮度之间存在反相关性。在该物体之前的耀斑中也观察到了类似的变化模式。电矢量位置角（EVPA）的变化显示出对物体亮度变化率的依赖性。EVPA 在耀斑期间变化很大，在强度缓慢变化时变化缓慢。