Articles written in Journal of Astrophysics and Astronomy
Volume 43 All articles Published: 15 February 2022 Article ID 0009 ACTIVE GALACTIC NUCLEI
We study flux and spectral variability of the high energy peaked TeV blazar PG 1553 $+$ 113 on diverse timescales using the data collected from 2005 to 2019 which also includes the intensive intra-night monitoring of the target. Additionally, we recorded the brightest flare of the blazar PG 1553 $+$ 113 during April 2019 when the source attained an $R$-band magnitude of 13.2. Analyzing the spectral evolution of the source during the flare gave a clockwise spectral hysteresis loop and a time lag with $V$-band variations leading to the $R$-band ones. Various statistical tests, fitting procedures and cross-correlation techniques are applied to search for periodicity and examine the color-magnitude relationship. We find a median period of ($2.21 \pm 0.04$) years along with the secondary period of about 210 days. Finally, we briefly discuss variousphysical mechanisms which are capable of explaining our findings.
Volume 44, 2023
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