Multi-band behaviour of the TeV blazar PG 1553+113 in optical range on diverse timescales

Abstract

Context. The TeV BL Lac object PG 1553+113 is one of the primary candidates for a binary supermassive black hole system. Aims. We study the flux and spectral variability of PG 1553+113 on intra-night to long-term timescales using (i) BVRI data collected over 76 nights from January 2016 to August 2019 involving nine optical telescopes and (ii) historical VR data (including ours) obtained for the period from 2005 to 2019. Methods. We analysed the light curves using various statistical tests, fitting and cross-correlation techniques, and methods for the search for periodicity. We examined the colour-magnitude diagrams before and after the corresponding light curves were corrected for the long-term variations. Results. Our intra-night monitoring, supplemented with literature data, result in a low duty cycle of ∼(10–18)%. In April 2019, we recorded a flare, which marks the brightest state of PG 1553+113 for the period from 2005 to 2019: R ≃ 13.2 mag. This flare is found to show a clockwise spectral hysteresis loop on its VR colour-magnitude diagram and a time lag in the sense that the V-band variations lead the R-band ones. We obtain estimates of the radius, the magnetic field strength, and the electron energy that characterize the emission region related to the flare. We find a median period of (2.21 ± 0.04) years using the historical light curves. In addition, we detect a secondary period of about 210 days using the historical light curves corrected for the long-term variations. We briefly discuss the possible origin of this period.

Characterizing the Optical Nature of the Blazar S5 1803+784 during Its 2020 Flare

“…According to the shock-in-jet scenario, the variability amplitude is larger at higher frequencies. This has been observed by many authors (e.g., Massaro et al 1998;Papadakis et al 2003;Dai et al 2011;Agarwal et al 2021b) and indicates that blazar spectra get steeper with a decrease in brightness and get flatter as brightness increases (Massaro et al 1998;Papadakis et al 2003). In many instances, the amplitude of variability of blazars at higher wavelengths is either comparable to or greater than that at lower wavelengths (Ghosh et al 2000).…”

“…During our observations, three telescopes were used, namely, the 1.0 m RC (T100) telescope, 60 cm RC robotic (T60) telescope, and 0.5 m RC (ATA50) telescope in Turkey. The technical details of the 1.0 m RC telescope and 60 cm RC robotic telescope are summarized in Agarwal et al (2021b) while the 0.5 m f/8 RC (ATA50) telescope is located at Ataturk University, Erzurum, and it is equipped with an Apogee Alta U230 2K charge-coupled device (CCD) with a field of view of 26 3 × 26 3, and standard Johnson BVR and Sloan Digital Sky Survey ugriz filters. A log of our photometric observations, along with the total period of observation on a particular night, is presented in Tables 1 and 2.…”

Multiwavelength analysis and modeling of OJ 287 during 2017–2020

“…In the period between Feb. 2019 -Jan. 2020, we performed observations of OJ 287 using five different telescopes around the globe: the 2.15 m Jorge Sahade telescope (JS, telescope A) and the 60 cm Helen Sawyer Hogg telescope (HSH, telescope B), CASLEO, Argentina; the 1.3 m JC Bhattacharya Telescope (JCBT; telescope C) at the Vainu Bappu Observatory (VBO), India. The technical descriptions of the above telescopes are summarized in Table 1 of Agarwal et al (2019) and Agarwal et al (2021). The number of observations made in each band on a particular date during our monitoring campaign is provided in Table 1.…”

A Possible Quasi-Periodic Oscillation in the X-ray Emission of 3C 120

“…Lomb-Scargle Periodogram (LSP) is a powerful tool widely used to search for periodicities in time series data (e.g., [17,40,41] and references therein). It was proposed by [42] and extended by [43].…”