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

TL;DR

This paper reports an extraordinary gamma-ray flare from the gravitationally lensed blazar PKS 1830-211, with significant gamma-ray variability but minimal changes at lower energies, highlighting a unique gamma-ray only flaring behavior.

Contribution

It presents the first detailed observation of a gamma-ray only flare in a gravitationally lensed blazar, revealing new insights into high-energy emission mechanisms.

Findings

Gamma-ray flux increased by a factor of ~12 during the flare.

No significant variability observed in NIR and X-ray bands.

PKS 1830-211 exhibits substantial gamma-ray variability without corresponding lower-energy changes.

Abstract

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 October and November 2010. The source experienced on October 14 a flux increase of a factor of ~ 12 with respect to its average value and kept brightest at this flux level (~ 500 x 10^{-8} ph cm^-2 sec^-1) for about 4 days. The 1-month gamma-ray light curve across the flare showed a mean flux F(E>100 MeV)= 200 x 10^{-8} ph cm^-2 sec^-1, which resulted in an enhancement by a factor of 4 with respect to the average value. Following the gamma-ray flare, the source was observed in NIR-Optical energy bands at the Cerro Tololo Inter-American Observatory and in X-rays by Swift/XRT and INTEGRAL/IBIS. The main result of these multifrequency observations is that the large variability observed in gamma-rays has not a significant counterpart at lower frequencies: no variation greater than a factor of ~ 1.5 resulted in 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.