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Spatial extension is an important characteristic for correctly associating gamma-ray-emitting sources with their counterparts at other wavelengths and for obtaining an unbiased model of their spectra. We present a new method for quantifying…

The parsec-scale radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been investigated using observations with the Very Long Baseline Array (VLBA). Comparisons between LAT…

High Energy Astrophysical Phenomena · Physics 2012-05-04 J. D. Linford , G. B. Taylor , R. W. Romani , J. F. Helmboldt , A. C. S. Readhead , R. Reeves , J. L. Richards

We investigate the gamma-ray and X-ray emission from the transient gamma-ray source Fermi J0035+6131, which was discovered with the Fermi Large Area Telescope (LAT) near the Galactic plane at $b=1.3^\circ$, and we discuss potential…

High Energy Astrophysical Phenomena · Physics 2018-10-16 Dirk Pandel , Philip Kaaret

The Fermi Large Area Telescope (LAT) is currently the most important facility for investigating the GeV $\gamma$-ray sky. With Fermi LAT more than three thousand $\gamma$-ray sources have been discovered so far. 1144 ($\sim40\%$) of the…

High Energy Astrophysical Phenomena · Physics 2016-09-07 G. Chiaro , D. Salvetti , G. La Mura , M. Giroletti , D. J. Thompson , D. Bastieri

Significant flares of GeV $\gamma$-ray emission from the Crab Nebula have been found by AGILE and Fermi-LAT years ago, indicating that extreme particle acceleration and radiation occurs in young pulsar wind nebulae. To enlarge the flare…

High Energy Astrophysical Phenomena · Physics 2021-02-24 Xiaoyuan Huang , Qiang Yuan , Yi-Zhong Fan

For over 15 years the Fermi Large Area Telescope (Fermi-LAT) has been monitoring the entire high-energy gamma-ray sky, providing the best sampled 0.1 -- $>1$ TeV photons to this day. As a result, the Fermi-LAT has been serving the…

High Energy Astrophysical Phenomena · Physics 2023-08-25 Janeth Valverde , D. Kocevski , M. Negro , S. Garrappa , A. Brill

We report on the results of X-ray and radio follow-up observations of two GeV gamma-ray sources 2FGL J0923.5+1508 and 2FGL J1502.1+5548, selected as candidates for high-redshift blazars from unassociated sources in the {\it Fermi} Large…

High Energy Astrophysical Phenomena · Physics 2015-06-16 Y. Takahashi , J. Kataoka , K. Niinuma , M. Honma , Y. Inoue , T. Totani , S. Inoue , T. Nakamori , K. Maeda

Blazars are the brightest and most abundant persistent sources in the extragalactic gamma-ray sky. Due to their significance, they are often observed across various energy bands to explore potential correlations between emissions at…

High Energy Astrophysical Phenomena · Physics 2024-01-22 P. Giommi , N. Sahakyan , D. Israyelyan , M. Manvelyan

Although not designed primarily as a polarimeter, the \textit{Fermi}-Large Area Telescope (LAT) has the potential to detect high degrees of linear polarization from some of the brightest gamma-ray sources. To achieve the needed accuracy in…

Instrumentation and Methods for Astrophysics · Physics 2019-08-14 Matteo Giomi , Rolf Bühler , Carmelo Sgrò , Francesco Longo , William Atwood

The production site and process responsible for the highly variable high-energy emission observed from blazar jets are still debated. Gravitational lenses can be used as microscopes to investigate the nature of such sources. We study the…

High Energy Astrophysical Phenomena · Physics 2025-10-09 Sarah M. Wagner , Jeffrey D. Scargle , Greg Madejski , Andrea Gokus , Krzysztof Nalewajko , Patrick Günther , Karl Mannheim

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with…

We present a search for Galactic transient gamma-ray sources using 13 years of the Fermi Large Area Telescope data. The search is based on a recently developed variable-size sliding-time-window (VSSTW) analysis and aimed at studying…

High Energy Astrophysical Phenomena · Physics 2023-01-11 Dmitry Prokhorov , Anthony Moraghan

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope observatory is a pair conversion telescope sensitive to gamma-rays over more than four energy decades, between 20 MeV and more than 300 GeV. Acting in synergy with the…

High Energy Astrophysical Phenomena · Physics 2019-08-14 Nicola Omodei

Blazars are a subclass of active galactic nuclei (AGN) that emit non-thermal radiation through relativistic jets, characterized by rapid flux and polarization variability. High synchrotron-peaked blazars (HSPs) and extreme high…

High Energy Astrophysical Phenomena · Physics 2025-11-26 Adithiya Dinesh , Alberto Dominguez , V. Paliya , J. L. Contreras , S. Buson , M. Ajello

The parsec-scale radio properties of 232 active galactic nuclei (AGNs), most of which are blazars, detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long…

High Energy Astrophysical Phenomena · Physics 2015-06-11 J. D. Linford , G. B. Taylor , F. K. Schinzel

Although the Fermi mission has increased our knowledge of gamma-ray AGN, many questions remain, such as the site of gamma-ray production, the emission mechanism, and the factors that govern the strength of the emission. Using data from a…

Cosmology and Nongalactic Astrophysics · Physics 2015-05-30 E. Nieppola , M. Tornikoski , E. Valtaoja , J. León-Tavares , T. Hovatta , A. Lähteenmäki , J. Tammi

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

We present the results of seven years of multicolour photometric monitoring of a sample of 31 $\gamma$-ray bright blazars using the RINGO3 polarimeter on the Liverpool Telescope from 2013--2020. We explore the relationships between…