The Remarkable γ-Ray Activity in the Gravitationally Lensed Blazar PKS 1830-211
Costa, E.; Barbiellini, G.; Longo, F.; Chen, A. W.; Giommi, P.; Popović, L. Č.; Pellizzoni, A.; Miller, H. R.; De Rosa, A.; Gianotti, F.; Feroci, M.; Kuulkers, E.; Del Monte, E.; Donnarumma, I.; Evangelista, Y.; Soffitta, P.; Trois, A.; Vercellone, S.; Pacciani, L.; Verrecchia, F.; Giusti, M.; Striani, E.; Vittorini, V.; Tavani, M.; Bulgarelli, A.; Giuliani, A.; Pucella, G.; Cattaneo, P. W.; Fuschino, F.; Lazzarotto, F.; Piano, G.; Trifoglio, M.; Pittori, C.; Lucarelli, F.; Simić, S.; Eggen, J.; Maune, J.
Italy, India, United States, Serbia, Chile, Spain
Abstract
We report the extraordinary γ-ray activity (E > 100 MeV) 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 × 10-8 photons cm-2 s-1) for about four days. The one-month γ-ray light curve across the flare showed a mean flux F(E > 100 MeV) = 200 × 10-8 photons cm-2 s-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 10-100 MeV. We discuss the theoretical implications of our findings.