Meenakshi Rajagopal | Searcharxiv

arXiv2020

Identifying the 3FHL Catalog. IV. Swift Observations of Unassociated Fermi-LAT 3FHL Sources

The Fermi Large Area Telescope (Fermi-LAT) 3FHL catalog is the latest catalog of >10 GeV sources and will remain an important resource for the high-energy community for the foreseeable future. Therefore, it is crucial that this catalog is made complete by providing associations for most sources. In this paper, we present the results of the X-ray analysis of 38 3FHL sources. We found a single bright X-ray source in 20 fields, two sources each in two fields and none for the remaining 16. The analysis of the properties of the 22 3FHL fields with X-ray sources led us to believe that most (19/22) are of extra-galactic origin. A machine-learning algorithm was used to determine the source type and we find that 15 potential blazars are likely BL Lacertae objects (BL Lacs). This is consistent with the fact that BL Lacs are by far the most numerous population detected above >10 GeV in the 3FHL.

astro-ph.HE↗

arXiv2019

Identifying the 3FHL catalog: CTIO results

Active galactic Nuclei (AGNs) with their relativistic jets pointed towards the observer, form a subclass of luminous gamma-ray sources commonly known as blazars. The study of blazars is essential to improve our understanding on the AGNs emission mechanisms and evolution, as well as to map the extragalactic background light. To do so, however, one needs to correctly classify and measure a redshift for a large sample of these sources. The Third {\it Fermi}--LAT Catalog of High-Energy Sources (3FHL) contains $\approx1160$ blazars reported at energies greater than $10$\,GeV. However $\sim$25\% of these sources are unclassified and $\sim$50\% lack of redshift information. To increase the spectral completeness of the 3FHL catalog, we are working on an optical spectroscopic follow up campaign using 4--m and 8--m telescopes. In this paper, we present the results of the second part of this campaign, where we observed 23 blazars using the 4\,$m$ telescope at CTIO in Chile. We report all the 23 sources to be classified as BL Lacs, a confirmed redshift measurement for 3 sources, a redshift lower limit for 2 sources and a tentative redshift measurement for 3 sources.

astro-ph.HE↗