Optical spectroscopic classification of a selection of Southern Hemisphere 3FHL blazar candidates

Abstract

ABSTRACT The Fermi-LAT has detected more than 7000 $\gamma$-ray sources which show emission above 50 MeV of which more than half are associated with blazars. However, the Fourth Fermi-LAT catalogue (4FGL-DR4) lists 1625 of these as blazar candidates of uncertain type. Increasing the number of classified Fermi-LAT sources is important for improving our understanding of extragalactic $\gamma$-ray sources and can be used to search for new classes of very high energy sources. We report on the optical spectroscopy of twelve blazar candidates with hard photon indices included in the Third Catalogue of Hard Fermi-LAT Sources during 2016 and 2017 using the SAAO 1.9-m telescope. We classify all the sources observed as BL Lac objects, and determine the potential spectroscopic redshift for seven of them.