Multi-wavelength observations of the lensed quasar PKS 1830−211 during the 2019 γ-ray flare

PKS 1830−211 is a γ-ray emitting, high-redshift (z = 2.507 ± 0.002), lensed flat-spectrum radio quasar. During the period mid-February to mid-April 2019, this source underwent a series of strong γ-ray flares that were detected by both AGILE-GRID and Fermi-LAT, reaching a maximum γ-ray flux of FE>100 MeV ≈ 2.3 × 10−5 photons cm−2 s−1. Here we report on a coordinated campaign from both on-ground (Medicina, OVRO, REM, SRT) and orbiting facilities (AGILE, Fermi, INTEGRAL, NuSTAR, Swift, Chandra), with the aim of investigating the multi-wavelength properties of PKS 1830−211 through nearly simultaneous observations presented here for the first time. We find a possible break in the radio spectra in different epochs above 15 GHz, and a clear maximum of the 15 GHz data approximately 110 days after the γ-ray main activity periods. The spectral energy distribution shows a very pronounced Compton dominance (> 200) which challenges the canonical one-component emission model. Therefore we propose that the cooled electrons of the first component are re-accelerated to a second component by, e.g., kink or tearing instability during the γ-ray flaring periods. We also note that PKS 1830−211 could be a promising candidate for future observations with both Compton satellites (e.g., e-ASTROGAM) and Cherenkov arrays (CTAO) which will help, thanks to their improved sensitivity, in extending the data availability in energy bands currently uncovered.