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Detection of quasi-periodic oscillations in the 37 GHz radio light curve of the blazar Ton 599 during 1990-2020

Alok C. Gupta, Alexandr E. Volvach, Shubham Kishore, Larisa N. Volvach, Paul J. Wiita, Lang Cui, Mauri J. Valtonen, Sandeep K. Mondal, Haritma Gaur

Abstract

Blazars are a subclass of radio-loud active galactic nuclei (AGNs) that display strong multi-wavelength variability on diverse timescales ranging from years down to minutes. In the last 1.5 decades, there have been occasional detections of quasi-periodic oscillations in several blazars in their time series data. We search for quasi-periodic oscillations (QPOs) in the 37 GHz radio band light curve of the flat-spectrum radio quasar Ton~599 made at the RT-22 radio telescope in Simeiz, Crimea, from 1990 to 2020. To identify and quantify the QPO nature of this radio light curve of Ton 599, we used the Lomb-Scargle periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ) analyses. We report the detection of a likely QPO of about 2.4 years in the 37 GHz radio light curves of Ton 599. We briefly discuss possible emission models for radio-loud active galactic nuclei that could explain such QPOs with periods of a few years.

Detection of quasi-periodic oscillations in the 37 GHz radio light curve of the blazar Ton 599 during 1990-2020

Abstract

Blazars are a subclass of radio-loud active galactic nuclei (AGNs) that display strong multi-wavelength variability on diverse timescales ranging from years down to minutes. In the last 1.5 decades, there have been occasional detections of quasi-periodic oscillations in several blazars in their time series data. We search for quasi-periodic oscillations (QPOs) in the 37 GHz radio band light curve of the flat-spectrum radio quasar Ton~599 made at the RT-22 radio telescope in Simeiz, Crimea, from 1990 to 2020. To identify and quantify the QPO nature of this radio light curve of Ton 599, we used the Lomb-Scargle periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ) analyses. We report the detection of a likely QPO of about 2.4 years in the 37 GHz radio light curves of Ton 599. We briefly discuss possible emission models for radio-loud active galactic nuclei that could explain such QPOs with periods of a few years.
Paper Structure (10 sections, 4 equations, 6 figures)

This paper contains 10 sections, 4 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Radio observations and analysis
  3. Results
  4. Discussion and conclusions
  5. Weighted wavelet Z (WWZ) analysis
  6. Generalized Lomb-Scargle periodogram (LSP) analysis
  7. REDFIT periodogram analysis
  8. Comparision of radio QPO with optical and $\gamma$-ray data
  9. Optical data and analysis
  10. Gamma-ray data and analysis

Figures (6)

  • Figure 1: Light curve of Ton 599 (yr: 1990 -- 2020), highlighting the portion of interest for periodicity searches.
  • Figure 2: WWZ map of light curve of Ton 599. The low-resolution region below the dashed white line represents the ROI.
  • Figure 3: Upper panel: LSP of the main segment of the light curve of Ton 599 from 1997 to 2020. The LSP fit is the mean of LSPs from $10^6$ simulated light curves; the 99.88% $\chi^2$ significance curve is evaluated following 2005AA...431..391V (see corresponding Eq. 16); the 99.92% (sim.) shows the percentile significance evaluated from the distribution of the simulated light curves' LSP powers. The QPO signal has been found to be at around the noted significance levels. Middle panel: As above, but for the entire set of observations from 1990 to 2020. Lower panel: As above, but for the restricted span 2006 to 2020.
  • Figure 4: REDFIT plot of the segmented light curve of Ton 599 (1997 -- 2020): b.c. spec. and th. spec. denote the bias-corrected spectrum and the fitted AR1 model spectrum, respectively.
  • Figure 5: Upper panel: R-band light curve from 2025AA...703A.259V binned into 15-day intervals, spanning from November 2011 to December 2020, and including points obtained with linear interpolation in gaps. Lower panel: LSP evaluation of the R-band binned and interpolated light curve.
  • ...and 1 more figures