Gamma-säteily aktiivisissa galakseissa

Despite vigorous research efforts, the origin of the gamma-ray emission from the active galactic nuclei (AGN) is still poorly understood. It is well-established that the gamma-rays are emitted from relativistic jets in AGN, but the exact location of the gamma-ray production zone in the jet is heavily debated and this uncertainty limits our ability to constrain the gamma-ray emission mechanism. The underlying problem is the limited angular resolution of gamma-ray telescopes that makes it impossible to image AGN at high energies and directly identify what part of the radio source is associated with the gamma-ray emission site. The most popular models to date associate the gamma-ray source either with the immediate vicinity of a black hole (<0.1 pc) or with the parsec-scale outflow (1-10pc). In order to get closer to the answer, we will combine high resolution imaging monitoring of over 300 parsec-scale jets at radio wavelengths from the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) Survey and 4+ years of gamma-ray monitoring data from the Large Area Telescope onboard NASA's Fermi Gamma-ray Space Telescope. We will analyze correlations between gamma-ray flares and brightening of the radio core as well as changes in the parsec scale radio jet structure. Our current data set is significantly larger than what has been used in such analyses before, and we expect to be able to draw statistically robust conclusions about a typical time delays between the gamma-ray flaring and ejection/flaring events seen in the radio images. The aim is to then assess the typical distance from the black hole at which most of the gamma-rays are produced.

Active galactic nuclei (AGN) are the most luminous, long-lasting objects in the Universe. Their energy source is believed to be accretion of matter onto a supermassive black hole. They sometimes show fast bi-polar outflows that serve as sites of efficient particle acceleration, rendering AGN as powerful emitters across the entire range of the electromagnetic spectrum, from radio to high-energy gamma-rays. One of the long-standing fundamental questions is the origin of the gamma-rays - where and how are they produced? The limited angular resolution of gamma-ray telescopes, compared to e.g. the radio telescope arrays, makes it impossible to image AGN at high energies and directly identify the gamma-ray emission site. The main goal of this project is to use an indirect approach to shed light on this problem. We will carry out a joint statistical analysis of temporal variations in gamma-ray emission and structural changes seen in high-resolution radio images for a large number of sources.