Articles written in Journal of Astrophysics and Astronomy
Volume 39 Issue 3 June 2018 Article ID 0030
We have reconsidered the simultaneous and homogeneous optical–IR light curves and the corresponding spectral indices curve of the blazarPKS0537–441 from January 2011 toMay2015. All the curves show significant fluctuations on various timescales, and the flux variations seem to be more pronounced towards the IR bands. The relation between average fluxes and spectral indices reveals the existence of redder-when-brighter (RWB) and bluer-when-brighter (BWB) trends at different flux levels, along with a long-term achromatic trend and a mild RWB trend on short-term timescales. Cross-correlation analyses present an energy-dependent time delay that the lower-frequency variations follow higher-frequency ones by a few weeks and a hysteresis pattern between spectra and fluxes. Our analysis reveals some potential coherence between low-energy-peaked BL Lacs (LBLs) and FSRQs, and indicates that the observed flux variability and spectral changes could be due to the superposition of a dominant jet emission, an underlying thermal contribution from a more slowly varyingdisk and/or other geometric effects under the shock-in-jet scenario.
Volume 42 All articles Published: 31 July 2021 Article ID 0092
We report the detection of quasi-periodic oscillations (QPOs) in the radio light curve of the blazar PKS 1510-089 spanning nearly 38 years, by means of the weighted wavelet Z-transform and Lomb–Scargle periodogram methods. Prominent QPOs with high confidence (>4$\sigma$) of $570\pm 30$, $800\pm 30$; and $1070\pm 40$ days in the 8 GHz light curve, $430\pm 10$ and $1080 \pm 30$ days in the 14.5 GHz light curve have been identified after estimating the significance against the red noise background. Moreover, the most significant QPO of about 1080 days exceeded 4$\sigma$ confidence level at two of the three frequencies but did not exactly persist the whole observations, indicating that QPOs in blazars are transient in nature. We suggest that the search for QPO in blazar light curves should evaluate the statistical significances and consider theinfluences of the colored noise, after reviewing earlier QPO claims of PKS 1510-089.
Volume 42, 2021
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