Multiband optical–IR variability of the blazar PKS 0537–441
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We have reconsidered the simultaneous and homogeneous optical–IR light curves and the corresponding spectral indices curve of the blazar PKS 0537–441 from January 2011 to May 2015. 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 varying disk and/or other geometric effects under the shock-in-jet scenario.
KeywordsGalaxies active BL lacertae objects general BL lacertae objects individual PKS 0537–441
This work is supported by the Science Research Project of Education Department of Yunnan Province, China (2017ZZX079, 2016ZZX230), and the Youth Program of the Applied Basic Research Projects of Yunnan Province, China (2017FD147). This paper has made use of up-to-date SMARTS optical/near-infrared light curves that are available at www.astro.yale.edu/smarts/glast/home.php.
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