The radio, optical, and γ-ray light curves of the blazar S5 1803+784, from the beginning of the Fermi-Large Area Telescope (LAT) mission in 2008 August–2018 December, are presented. The aim of this work is to look for correlations among different wavelengths useful for further theoretical studies. We analysed all the data collected by Fermi-LAT for this source, taking into account the presence of nearby sources, and we collected optical data from our own observations and public archive data to build the most complete optical and γ-ray light curve possible. Several γ-ray flares (F > 2.3 10−7ph(E > 0.1 GeV) cm−2 s−1) with optical coverage were detected, all but one with corresponding optical enhancement; we also found two optical flares without a γ-ray counterpart. We obtained two Swift Target of Opportunity observations during the strong flare of 2015. Radio observations performed with VLBA and EVN through our proposals in the years 2016–2020 were analysed to search for morphological changes after the major flares. The optical/γ-ray flux ratio at the flare peak varied for each flare. Very minor optical V − I colour changes were detected during the flares. The X-ray spectrum was well fitted by a power law with photon spectral index α = 1.5, nearly independent of the flux level: No clear correlation with the optical or the γ-ray emission was found. The γ-ray spectral shape was well fitted by a power law with average photon index α = 2.2. These findings support an inverse-Compton origin for the high-energy emission of the source, nearly co-spatial with the optically emitting region. The radio maps showed two new components originating from the core and moving outwards, with ejection epochs compatible with the dates of the two largest γ-ray flares.

中文翻译：

---

耀变体 S5 1803+784 的多波长耀斑观测

展示了 2008 年 8 月至 2018 年 12 月费米大区域望远镜 (LAT) 任务开始时 blazar S5 1803+784 的射电、光学和 γ 射线光变曲线。这项工作的目的是寻找对进一步理论研究有用的不同波长之间的相关性。我们分析了 Fermi-LAT 为该源收集的所有数据，考虑到附近源的存在，我们从我们自己的观测和公共档案数据中收集了光学数据，以构建尽可能完整的光学和 γ 射线光曲线。检测到几个具有光学覆盖的γ射线耀斑（F > 2.3 10-7ph(E > 0.1 GeV) cm-2 s-1），除了一个具有相应的光学增强外；我们还发现了两个没有 γ 射线对应物的光学耀斑。我们在 2015 年的强烈耀斑期间获得了两次 Swift 机会目标观测。通过我们在 2016 年至 2020 年的建议，对 VLBA 和 EVN 进行的射电观测进行了分析，以寻找主要耀斑后的形态变化。耀斑峰值处的光通量/γ射线通量比随每个耀斑而变化。在耀斑期间检测到非常小的光学 V - I 颜色变化。X 射线光谱很好地符合光子光谱指数 α = 1.5 的幂律，几乎与通量水平无关：没有发现与光学或 γ 射线发射的明确相关性。γ 射线光谱形状很好地符合平均光子指数 α = 2.2 的幂律。这些发现支持源的高能发射的逆康普顿起源，几乎与光学发射区域共空间。