Multiwavelength 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 2019 mid-February to mid-April, this source underwent a series of strong γ-ray flares that were detected by both AGILE- GRID (Gamma-Ray Imaging Detector) and Fermi Large Area Telescope ( Fermi -LAT), reaching a maximum γ-ray flux of F E > 100 MeV ≈2 . 3 ×10 -5 photons cm -2 s -1 . Here, we report on a coordinated campaign from both on-ground [Medicina, Owens Valley Radio Observatory (OVRO), Rapid Eye Mount (REM), and Sardinia Radio Telescope (SRT)] and orbiting facilities (AGILE, Fermi , INTEGRAL , NuSTAR , Swift , and Chandra ), with the aim of investigating the multiwavelength 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 abo v e 15 GHz, and a clear maximum of the 15 GHz data approximately 110 d 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, for example, 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. enhanced ASTROGAM (e-ASTROGAM)] and Cherenkov arrays [Cherenkov Telescope Array Observatory (CTAO)] which will help, thanks to their impro v ed sensitivity, in extending the data availability in energy bands currently unco v ered.