Fermi Gamma-ray Space Telescope

4LAC source SED fitting: a cooperative social experiment in the LAT Collaboration

Stefano Ciprini


Several parallel activities are ongoing for the construction of the next Fourth LAT AGN Catalog (4LAC), a catalog of gamma-ray blazars and other AGN companion and subsidiary of the forthcoming 8-year Fermi LAT Fourth Source general Catalog 4FGL. Among them one can be defined as a cooperative effort within the Fermi LAT Collaboration, that is addressed to fit the synchrotron components of the spectral energy distributions (SEDs) of preliminary and statistically-associated AGN/blazar candidate counterparts in the error ellipses of the 4FGL catalog sources. This sort of "human-pipeline" allowed us to manually inspect and fit, one-by-one, the SEDs of about 3000 preliminary sources for the next 4LAC catalog. The work is both based on source association software with two methods developed by the LAT Collaboration (Bayesian and Likelihood ratio methods, used in previous 2LAC, 3LAC, 2FHL, 3FHL catalogs) and on the SED Builder web tool at the Space Science Data Center of ASI in Rome. This social routine project performed thanks to 33 collaborators among professional scientists and students within the LAT Collaboration and a couple of non professional individuals, could open the way to future ideas for citizen science (also known as community/civic/crowd-sourced/networked science) projects related to Fermi LAT gamma-ray AGN science and catalogs.