Multiwavelength observations of the lensed quasar PKS 1830-211 during the 2019 γ-ray flare

Abstract

<p>PKS 1830-211 is a <em>γ</em>-ray emitting, high-redshift (<em>z</em> =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 <em>γ</em>-ray flares that were detected by both AGILE-GRID (Gamma-Ray Imaging Detector) and <em>Fermi </em>Large Area Telescope (<em>Fermi</em>-LAT), reaching a maximum <em>γ</em>-ray flux of <em>F</em>_{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, <i>Fermi</i>, <i>INTEGRAL</i>, <i>NuSTAR</i>, <i>Swift</i>, and <i>Chandra</i>), 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 above 15 GHz, and a clear maximum of the 15 GHz data approximately 110 d after the <em>γ</em>-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 <em>γ</em>-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 improved sensitivity, in extending the data availability in energy bands currently uncovered.<br></p>