Is PKS 0625-354 another variable TeV active galactic nucleus?

TL;DR

This paper reports the detection of gamma-ray variability in the active galaxy PKS 0625-354 using H.E.S.S. telescopes, providing new insights into gamma-ray emission mechanisms in non-blazar AGN.

Contribution

It presents the first detailed gamma-ray variability study of PKS 0625-354, challenging its classification and expanding understanding of non-blazar AGN emission.

Findings

Detected gamma-ray variability with >5sigma significance

Observed flux decrease over nine nights

Constructed multi-band spectral energy distribution

Abstract

The majority of the active galactic nuclei (AGN) detected at very-high-energies above 100 GeV belong to the class of blazars with a small angle between the jet-axis and the line-of-sight. Only about 10 percent of the gamma-ray AGN are objects with a larger viewing angle resulting in a smaller Doppler boosting of the emission. Originally, it was believed that gamma-ray emission can only be observed from blazars and those are variable in its brightness. Instead, the last years have shown that non-blazar active galaxies also show a fascinating variability behaviour which provide important new insights into the physical processes responsible for the gamma-ray production and especially for flaring events. Here, we report on the observation of gamma-ray variability of the active galaxy PKS 0625-354 detected with the H.E.S.S. telescopes in November 2018. The classification of PKS 0625-354 is a still matter of debate. The H.E.S.S. measurements were performed as part of a flux observing program and showed in the first night of the observation a detection of the object with >5sigma. A denser observation campaign followed for the next nine nights resulting in a decrease of the gamma-ray flux. Those observations were accompanied with Swift in the X-ray and UV/optical band allowing for the reconstruction of a multi-band broad-band spectral energy distribution. We will discuss the implications of the gamma-ray variability of the object.