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Since the launch of the Fermi satellite, BL Lacertae has been moderately active at gamma-rays and optical frequencies until May 2011, when the source started a series of strong flares. The exceptional optical sampling achieved by the…

High Energy Astrophysical Phenomena · Physics 2019-08-14 C. M. Raiteri , M. Villata , F. D'Ammando , V. M. Larionov , M. A. Gurwell , D. O. Mirzaqulov , P. S. Smith

Ever since the discovery by the Fermi mission that active galactic nuclei (AGN) produce copious amounts of high-energy emission, its origin has remained elusive. Using high-frequency radio interferometry (VLBI) polarization imaging, we…

High Energy Astrophysical Phenomena · Physics 2018-05-15 B. Rani , S. G. Jorstad , A. P. Marscher

The launch of the Fermi Gamma-ray Space Telescope has heralded a new era in the study of gamma-ray pulsars. The population of confirmed gamma-ray pulsars has gone from 6-7 to more than 60, and the superb sensitivity of the Large Area…

High Energy Astrophysical Phenomena · Physics 2015-05-19 Paul S. Ray , Pablo M. Saz Parkinson

The Fermi All-sky Variability Analysis (FAVA) provides a photometric alternative for identifying week-long gamma-ray flares across the entire sky while being independent of any diffuse Galactic or isotropic emission model. We reviewed 779…

High Energy Astrophysical Phenomena · Physics 2024-02-29 Scott D. Joffre , Núria Torres-Albà , Marco Ajello , Daniel Kocevski , Rolf Buehler

The use of Bayesian neural networks is a novel approach for the classification of gamma-ray sources. We focus on the classification of Fermi-LAT blazar candidates, which can be divided into BL Lacertae objects and Flat Spectrum Radio…

High Energy Astrophysical Phenomena · Physics 2022-05-13 Anja Butter , Thorben Finke , Felicitas Keil , Michael Krämer , Silvia Manconi

The classification of gamma-ray-detected blazar candidates of uncertain type (BCU) is a relevant problem in extragalactic gamma-ray astronomy. Here we report the optical spectroscopic characterization, using two 3-4~m class telescopes,…

We report on the results of deep X-ray follow-up observations of four unidentified Fermi/LAT gamma-ray sources at high Galactic latitudes using Suzaku. The studied objects were detected with high significance during the first 3 months of…

The Large Area Telescope (LAT) aboard the Fermi satellite allows us to study the high-energy gamma-ray sky with unprecedented sensitivity. However, the origin of 31% of the detected gamma-ray sources remains unknown. This population of…

High Energy Astrophysical Phenomena · Physics 2015-05-27 Hannes-S. Zechlin , Dieter Horns

The Fermi-LAT DR1 and DR2 4FGL catalogues feature more than 5000 gamma-ray sources of which about one fourth are not associated with already known objects, and approximately one third are associated with blazars of uncertain nature. We…

High Energy Astrophysical Phenomena · Physics 2021-06-30 S. Germani , G. Tosti , . Lubrano , S. Cutini , I. Mereu , A. Berretta

Blazars are the most common sources of $\gamma$-ray photons in the extragalactic sky. Their $\gamma$-ray light curves are characterized by bright flaring episodes, similarly to what is observed at longer wavelengths. These gamma-ray bursts…

High Energy Astrophysical Phenomena · Physics 2025-06-04 Matteo Cerruti

The Fermi-LAT has detected more than 3000 sources in the GeV $\gamma$-ray regime. The majority are extra-galactic and these sources are dominated by blazars. However, $\sim28$ per cent of the sources in Fermi 3LAC are listed as blazar…

High Energy Astrophysical Phenomena · Physics 2017-02-01 L. Klindt , B. van Soelen , P. J. Meintjes , P. Väisänen

Associating gamma-ray sources to their low-energy counterparts is one of the major challenges of modern gamma-ray astronomy. In the context of the Fourth Fermi Large Area Telescope Source Catalog (4FGL), the associations rely mainly on…

High Energy Astrophysical Phenomena · Physics 2020-06-03 Raniere de Menezes , Raffaele D'Abrusco , Francesco Massaro , Dario Gasparrini , Rodrigo Nemmen

Significant progress in the classification of Fermi unassociated sources , has led to an increasing number of blazars are being found. The optical spectrum is effectively used to classify the blazars into two groups such as BL Lacs and flat…

Instrumentation and Methods for Astrophysics · Physics 2020-06-10 Yijun Xu , Weirong Huang , Hui Deng , Ying Mei , Feng Wang

We present multi-epoch optical spectroscopy of seven southern Fermi-monitored blazars from 2008 - 2013 using the Small and Medium Aperture Research Telescope System (SMARTS), with supplemental spectroscopy and polarization data from the…

High Energy Astrophysical Phenomena · Physics 2015-11-11 Jedidah C. Isler , C. M. Urry , C. Bailyn , P. S. Smith , P. Coppi , M. Brady , E. Macpherson , I. Hasan , M. Buxton

Machine learning (ML) and deep learning (DL) techniques are increasingly used across astrophysics, enabled by the growing availability of data and improved acquisition methods. These approaches now support tasks from redshift estimation to…

High Energy Astrophysical Phenomena · Physics 2025-07-09 E. Oukacha , Y. Becherini

Context: GeV gamma-ray pulsations from over 140 pulsars have been characterized using the Fermi Large Area Telescope, enabling improved understanding of the emission regions within the neutron star magnetospheres, and the contributions of…

We perform a blind search for the variability of the gamma-ray sky in the energy range E>1 GeV using 308 weeks of the Fermi-LAT data. We use the technique based on the comparison of the weekly photon counts and exposures in sky pixels by…

High Energy Astrophysical Phenomena · Physics 2015-12-22 M. S. Pshirkov , G. I. Rubtsov

Fermi Gamma-ray Space Telescope has detected a diverse range of gamma-ray transients since its launch in 2008. Over the years, Fermi has accumulated an extensive public archive of transient events. Traditional classification methods for…

High Energy Astrophysical Phenomena · Physics 2026-03-31 Arpan Aryam John , Krushna Govind Shete , Shabnam Iyyani , Saptarshi Bej

Nearly one-third of the gamma-ray sources detected by Fermi are still unidentified, despite significant recent progress in this effort. On the other hand, all the gamma-ray extragalactic sources associated in the second Fermi-LAT catalog…

High Energy Astrophysical Phenomena · Physics 2019-08-19 F. Massaro , R. D'Abrusco , A. Paggi , N. Masetti , M. Giroletti , G. Tosti , Howard A. Smith , S. Funk