Searching for new very high energy emitting AGN among the unclassifed and unassociated Fermi-LAT sources

[摘要] English: Jet dominated Active Galactic Nuclei (AGN) are the most energetic persistent sources of emissionin the universe, emitting radiation across the entire electromagnetic spectrum. When these jetsare pointed towards the observer, they become known as blazars. Blazar emission is dominatedby the beamed non-thermal emission from the relativistic jet and are the brightest sources in theextragalactic sky. Blazars, sub-categorized into BL Lacertae objects (BL Lacs) and Flat SpectrumRadio Quasars (FSRQs) exhibit variability at all wavelengths on diverse timescales, highpolarization and weak or featureless optical spectra. These extreme sources provide a laboratoryto test some of the most energetic physical processes in the known universe. In order to study theprocesses responsible for the highest energy emission originating from blazar jets, more Very HighEnergy (VHE) emitting blazars must be found and studied with Imaging Air Cherenkov Telescopes(IACTs). The small sample of currently known VHE emitting blazars, studied for many years,has not yet provided a complete understanding of blazar physics. A study to monitor 17 VHEblazars detected by the High Energy Stereoscopic System (H.E.S.S.) with the Watcher RoboticTelescope has been underway since May 2015. A fast reduction and analysis pipeline, written inpython and using PyRAF to interface with IRAF, was developed to perform aperture photometryon 14 of these sources and search for long-term variability (LTV). In addition, to search for newVHE emitting blazars observable with IACTs, a sample of 11 Blazar Candidates of UncertainType (BCUs) listed in the Third Fermi Large Area Telescope Source Catalog (3FGL), 11 BCUsand an unassociated source listed in the Third Catalogue of Hard Large Area Telescope sources(3FHL), selected based on hard -ray spectra and lack of redshift measurements were identi edfor spectroscopic follow-up with the aim of classifying them. The selected sources were observedwith the SpUpNIC grating spectrograph mounted on the SAAO 1.9-m telescope. A selection of6 3FHL sources identi ed for spectroscopic study were also observed with the Sutherland HighspeedOptical Camera (SHOC) mounted on the SAAO 1.0-m telescope to search for intra-dayvariability (IDV). All 22 of the BCUs were classi ed as BL Lac objects based on the absence ofstrong emission lines and a diluted Ca break (less than 40%). Further, redshifts were calculatedfor 11 BCUs and potential redshifts for 4 BCUs. Further searches for photometry variability wereundertaken for all sources. Spectral Energy Distributions (SEDs) were constructed to determinewhich of the observed BCUs were good candidates to be observed with IACTs. The 50h H.E.S.S.and Cherenkov Telescope Array (CTA) South sensitivity curves were overlayed on the SEDs. Ofthe BCUs observed, 8 of the sources have -ray emission above the CTA detection threshold andare good candidates for VHE observation.

[发布机构] University of the Free State