Multiwavelength periodicity search in a sample of ?-ray bright blazars

ABSTRACT We present the results of a long-term periodicity search in sample ?-ray blazars within multiwavelength context. These have been selected from Steward Observatory as part its optical monitoring program between 2008 and 2018. study 15 sources with temporal coverage their total polarized emission sufficiently large (>9 yr) to perform reliable analysis. collect data several observatories extend coverage, enabling longer periods. In addition, are also gathered high-energy (E > 100 MeV) band Fermi Large Area Telescope; GHz radio Owens Valley Radio Observatory. identify 5 promising candidates host quasi-periodic emission, AO 0235+164, PKS 1222+216, Mrk 501, BL Lacertae, 1ES 2344+514 periods one or more bands statistical significances ?3? after trial factor correction. 0235+164 shows period ?8.2 yr R band; 1222+216 has modulation ?1.6 yr; 501 displays ?5 quasi-periodicity wavelengths; Lacertae presents ?1.8 emission; 2344 + 514 hint ?5.5 band. interpret these framework most common models scenarios, namely presence binary supermassive black hole system; geometrical effects like helical precessing jets.