A Multiwavelength Study to Decipher the 2017 Flare of the Blazar OJ 287

In 2017 February, the blazar OJ 287 underwent a period of intense multiwavelength activity. It reached a new historic peak in the soft X-ray (0.3-10 keV) band, as measured by the Swift X-ray Telescope. This event coincides with a very-high-energy (VHE) γ-ray outburst that led VERITAS to detect emission above 100 GeV, with a detection significance of 10σ (from 2016 December 9 to 2017 March 31). The time-averaged VHE γ-ray spectrum was consistent with a soft power law (Γ = −3.81 ± 0.26) and an integral flux corresponding to ∼2.4% that of the Crab Nebula above the same energy. Contemporaneous data from multiple instruments across the electromagnetic spectrum reveal a complex flaring behavior, primarily in the soft X-ray and VHE bands. To investigate the possible origin of such an event, our study focuses on three distinct activity states: before, during, and after the 2017 February peak. The spectral energy distributions during these periods suggest the presence of at least two nonthermal emission zones, with the more compact one responsible for the observed flare. Broadband modeling results and observations of a new radio knot in the jet of OJ 287 in 2017 are consistent with a flare originating from a strong recollimation shock outside the radio core.