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A blazar is an active galactic nucleus (AGN) whose relativistic jet is directed nearly along the line of sight. This jet emits light at all wavelengths. To study these astrophysical sources accurately, we need to know their distance from the observer, which is estimated through their cosmological redshift. The luminosity of blazar jets is so great that the emission of the host galaxy is generally masked by that of the jet, making spectroscopic analysis of the galaxy difficult. Fortunately, blazars are  variable sources, with large fluctuations in luminosity. On short timescales, the blazar may be in a low-enough flux state for the host galaxy to be detectable, making it possible to extract the distance via spectroscopic observations. The aim of the internship is therefore to be able to react to, or even anticipate, a blazar’s low-flux state, in order to initiate spectroscopic monitoring that will improve our knowledge of the spatial distribution of these objects.

This internship proposes to use blazar data collected by the Fink platform since 2019, based in particular on observations from the Zwicky Transient Facility which is a pathfinder for the Vera C. Rubin Observatory / LSST. Fink is a numerical platform that collects and analyzes massive, real-time data streams that consist of flux variations of astronomical bodies. The physical processes behind these variations are manifold, and the variations are found on all scales, from our solar system (e.g. asteroids, comets) to our galaxy (e.g. variable stars, exoplanets) and beyond (e.g. supernovae, kilonova, AGN, gamma-ray bursts).

In the first part of the internship, the student will use available tools and catalogs to distinguish gamma-ray blazars from other astrophysical signals in Fink data. The second part of the internship will focus on understanding the variability of these sources. In particular, this involves developing techniques for reacting to or even anticipating a decrease in flux, and for broadcasting information in real time to astronomers observing the host galaxy. The student will also have the opportunity to work on correlations with data from other observatories, and thus reveal the multi-messenger nature of the underlying physical phenomena.

The student will have unrestricted access to the VirtualData cloud at the Université Paris-Saclay, to data from the Fink project (ZTF, Fermi, Swift, etc) and will be able to contribute to the work of the Redshift task-force of the CTA Consortium.