On the Connection Between the Gamma-ray and (Sub-)mm Emission in Active Galactic Nuclei

Abstract

This research investigates the connection between the submillimetre (sub-mm), millimetre (mm) and gamma-ray emission in a sample eight blazars (consisting of high- and intermediate-frequency peaked BL Lacertae Objects (HBLs and IBLs respectively) as well as Flat Spectrum Radio Quasars (FSRQs)) and one radio galaxy. Light curves using both short-term (~6 days to ~3 months) and long-term (5.5 - 12 years) observations at gamma-ray and (sub-)mm wavebands are presented. Long-term light curves at (sub-)mm wavelengths show evidence that emission at these wavelengths is source class dependent. Similarities in emission patterns and flux variability were observed between FSRQs and IBLs. The correlation between emission at 1.35 mm and the 100 MeV to 100 GeV gamma-ray wavebands was studied both qualitatively and statistically using the discrete correlation function (DCF) method. Results from the DCF analysis showed that while all sources exhibit different behavioural patterns at different epochs, some general trends can be drawn based on the source type. It was found that IBLs behaved more like FSRQs than HBLs, although IBLs are classified as BL Lacertae objects, with HBLs showing the weakest correlation and variability at both emission bands and FSRQs showing the strongest evidence for correlation and variability within this sample set. This provides further evidence for the hypothesis of the unified Active Galactic Nuclei model, in which these objects evolve from FSRQ type blazars into IBLs and then into HBLs. This is because IBLs exhibit behavioural patterns of both FSRQs and BL Lacertae objects. In addition to this, time delay analysis of 3C 454.3, BL Lacertae and 3C 273 in the correlation study yielded separation distances between the emission regions ranging between ~0.1 pc to ~19 pc in the rest frame of the observer. These are in agreement with other studies in the literature (e.g. (214;42)). However, much greater separation distances were observed for 3C 279 and OJ 287 (> 70 pc). These findings suggest that the nature and geometry of blazar jets are highly complex and vary from epoch to epoch. It was concluded that extensive consistent long-term multiwavelength studies of a larger sample of sources from all blazar sub-classes would help further constrain the location of the wavelength-dependent emission regions in the jet.