Radio and gamma-ray follow-up of the exceptionally high activity state of PKS 1510-089 in 2011

TL;DR

This study analyzes the multiwavelength variability of PKS 1510-089 during its 2011 high activity period, revealing correlations between gamma-ray, optical, and radio emissions, and suggesting the gamma-ray region is located downstream in the jet.

Contribution

It provides a detailed multiwavelength analysis of PKS 1510-089's 2011 activity, linking gamma-ray flares to radio outbursts and jet dynamics, offering insights into emission region locations.

Findings

Gamma-ray and radio fluxes peaked simultaneously during the 2011 outbursts.

Optical polarization angle rotated by about 380 degrees during a gamma-ray flare.

Radio outburst lagged behind gamma-ray flares, indicating emission regions are downstream in the jet.

Abstract

We investigate the radio and gamma-ray variability of the flat spectrum radio quasar PKS 1510-089 in the time range between 2010 November and 2012 January. In this period the source showed an intense activity, with two major gamma-ray flares detected in 2011 July and October. During the latter episode both the gamma-ray and the radio flux density reached their historical peak. Multiwavelength analysis shows a rotation of about 380 deg of the optical polarization angle close in time with the rapid and strong gamma-ray flare in 2011 July. An enhancement of the optical emission and an increase of the fractional polarization both in the optical and in radio bands is observed about three weeks later, close in time with another gamma-ray outburst. On the other hand, after 2011 September a huge radio outburst has been detected, first in the millimeter regime followed with some time delay at centimeter down to decimeter wavelengths. This radio flare is characterized by a rising and a decaying stage, in agreement with the formation of a shock and its evolution, as a consequence of expansion and radiative cooling. If the gamma-ray flare observed in 2011 October is related to this radio outburst, then this strongly indicates that the region responsible for the gamma-ray variability is not within the broad line, but a few parsecs downstream along the jet.