The vanishing of the primary emission region in PKS 1510-089

TL;DR

In July 2021, PKS 1510-089 showed a dramatic decrease in high-energy gamma-ray and optical fluxes, indicating the vanishing of the primary emission region, while very-high-energy gamma-ray and X-ray fluxes remained steady, suggesting different emission zones.

Contribution

This study provides evidence for the disappearance of the primary emission region in PKS 1510-089 and proposes possible geometric or efficiency changes in the jet as explanations.

Findings

High-energy gamma-ray and optical fluxes dropped significantly.

Very-high-energy gamma-ray and X-ray fluxes remained steady.

Optical polarization vanished, indicating changes in the emission region.

Abstract

In July 2021, PKS 1510-089 exhibited a significant flux drop in the high-energy gamma-ray (by a factor 10) and optical (by a factor 5) bands and remained in this low state throughout 2022. Similarly, the optical polarization in the source vanished, resulting in the optical spectrum being fully explained through the steady flux of the accretion disk and the broad-line region. Unlike the aforementioned bands, the very-high-energy gamma-ray and X-ray fluxes did not exhibit a significant flux drop from year to year. This suggests that the steady-state very-high-energy gamma-ray and X-ray fluxes originate from a different emission region than the vanished parts of the high-energy gamma-ray and optical jet fluxes. The latter component has disappeared through either a swing of the jet away from the line-of-sight or a significant drop in the photon production efficiency of the jet close to the black hole. Either change could become visible in high-resolution radio images.