The remarkable γ-ray activity in the gravitationally lensed blazar PKS 1830-211

Abstract

We report the extraordinary γ-ray activity (E > 100MeV) of the gravitationally lensed blazar PKS 1830-211 (z = 2.507) detected by AGILE between 2010 October and November. On October 14, the source experienced a factor of ∼12 flux increase with respect to its average value and remained brightest at this flux level (∼500 × 10-8photonscm-2s -1) for about four days. The one-month γ-ray light curve across the flare showed a mean flux F(E > 100MeV) = 200 × 10 -8photonscm-2s-1, which resulted in a factor of four enhancement with respect to the average value. Following the γ-ray flare, the source was observed in near-IR (NIR)-optical energy bands at the Cerro Tololo Inter-American Observatory and in X-Rays by Swift/X-Ray Telescope and INTEGRAL/IBIS. The main result of these multifrequency observations is that the large variability observed in γ-rays does not have a significant counterpart at lower frequencies: no variation greater than a factor of ∼1.5 appeared in the NIR and X-Ray energy bands. PKS 1830-211 is then a good "γ-ray only flaring" blazar showing substantial variability only above 10-100MeV. We discuss the theoretical implications of our findings. © 2011. The American Astronomical Society. All rights reserved.