Abstract
BL Lac object 3C 371 is variable in optical and radio range, according to long-term monitoring data, for example AAVSO (American Association of Variable Star Observers) and OVRO (Owens Valley Radio Observatory). In addition, some authors note intra-night variability. However, in terms of access, just a few works are devoted to this topic, and questions remain about intra-day variability in radio range. The purpose of the work is to search for fast variability in radio (5, 6.1, 6.7 GHz) and optical bands (V, R, I) using international cooperation in 2019 and 2020 observation sessions. The 16-m radio telescope VIRAC, in Latvia, as well as optical telescopes AZT-3 (Mayaki, Ukraine), VNT (Vihorlat, Slovakia), and Schmidt camera (Baldone, Latvia) were used. To analyze variability, the STFT method of spectrograms and Lomb–Scargle periodograms for non-uniform time series were used. As result of the work, there is no correlation between optical and radio observations, and no significant quasi-harmonic variability was detected in radio range, but there is irregular low amplitude variability. In the optical range, there is variability with a characteristic time of about seven days and possibly less. Cyclical variability of 3C 371 was found in the optical range, and intra-day variability in radio range is most likely absent, as there are irregular variations and noise. It is planned to continue joint radio-optical observations 3C 371 to accumulate the necessary statistics.
Highlights
3C 371 refers to BL Lacertae type objects and is located in the Draco constellation of the northern sky, and is one of the closest and brightest objects of this type
It is assumed that the angle between the jet axis and the observer’s line of sight is less than 18◦ [1], but during a long-term (1994–2020) study the angular structure of 3C 371 in the radio range on the North American VLBA system, superluminal velocities of the bright components of the jet were not detected, which is unusual for BL Lac objects
The 16-m radio telescope is equipped with a cryogenic full power receiver (in two circular polarization, left (LCP) and right (RCP)), tuned to frequencies 5, 6.1, 6.7, and 8 GHz, with a back-end SDR-detector allowing for quick adjustment of the receiving parameters
Summary
3C 371 refers to BL Lacertae type objects (type of active galactic nucleus, named after its prototype, BL Lacertae) and is located in the Draco constellation of the northern sky, and is one of the closest and brightest objects of this type. 3C 371 has a radio jet, and an optical jet, discovered from observations at a ground telescope and confirmed by observations at the Hubble Space. It is assumed that the angle between the jet axis and the observer’s line of sight is less than 18◦ [1], but during a long-term (1994–2020) study the angular structure of 3C 371 in the radio range on the North American VLBA system, superluminal velocities of the bright components of the jet were not detected (http://www.physics.purdue.edu/astro/MOJAVE/sourcepages/1807+698.shtml), which is unusual for BL Lac objects. Old photographic plates with 3C 371 images, obtained since 1895, are well preserved, which made it possible to estimate the amplitude of optical variability of this object in the limit ±1.5 m [3]
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