The Remarkable gamma-Ray Activity in the Gravitationally Lensed Blazar PKS 1830-211

We report the extraordinary gamma-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<SUP>-8</SUP> photons cm<SUP>-2</SUP> s<SUP>-1</SUP>) for about four days. The one-month gamma-ray light curve across the flare showed a mean flux F(E > 100 MeV) = 200 10<SUP>-8</SUP> photons cm<SUP>-2</SUP> s<SUP>-1</SUP>, which resulted in a factor of four enhancement with respect to the average value. Following the gamma-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 gamma-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 "gamma-ray only flaring" blazar showing substantial variability only above 10-100 MeV. We discuss the theoretical implications of our findings.