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This paper presents the gamma-ray spectral and timing results from the long-term regular observations of Mrk 421 with the Large Area Telescope (LAT) onboard Fermi during 2008 August - 2023 August. We discerned six periods the relatively…

High Energy Astrophysical Phenomena · Physics 2025-03-05 B. Kapanadze , A. Gurchumelia , M. Aller

Even with several thousand {\it Fermi}-LAT blazar detections, the $\gamma$-ray emission mechanism is poorly understood. We explore correlated optical/$\gamma$-ray flux variations for 178 {\it Fermi}-LAT blazars regularly monitored by KAIT,…

High Energy Astrophysical Phenomena · Physics 2019-07-31 I. Liodakis , R. W. Romani , A. V. Filippenko , D. Kocevski , W. Zheng

In this work, we study the short term flaring activity from the high synchrotron peaked blazar Mrk 501 detected by the FACT and H.E.S.S. telescopes in the energy range 2-20 TeV during June 23-24, 2014 (MJD 56831.86-56831.94). We revisit…

High Energy Astrophysical Phenomena · Physics 2018-12-26 K K Singh , H Bhatt , S Bhattacharyya , N Bhatt , A K Tickoo , R C Rannot

The gamma-ray survey of the sky by the Fermi Gamma-ray Space Telescope offers both opportunities and challenges for multiwavelength and multi-messenger studies. Gamma-ray bursts, pulsars, binary sources, flaring Active Galactic Nuclei, and…

High Energy Astrophysical Phenomena · Physics 2019-08-13 D. J. Thompson

In this work, I have presented a multi-frequency variability and correlation study of the blazar Ton 599, which was observed first time in flaring state at the end of 2017. Data from \textit{Fermi}-LAT, Swift-XRT/UVOT, Steward Observatory,…

High Energy Astrophysical Phenomena · Physics 2019-01-30 Raj Prince

Fermi-LAT >30 MeV observations have increased the number of detected solar flares by almost a factor of 10 with respect to previous space observations. These sample both the impulsive and long duration phases of GOES M and X class flares.…

Solar and Stellar Astrophysics · Physics 2019-08-14 Melissa Pesce-Rollins , Nicola Omodei , Vahe' Petrosian , Wei Liu , Fatima Rubio da Costa , Alice Allafort

BL Lac objects are an extreme type of active galactic nuclei (AGNs) that belong to the largest population of $\gamma$-ray sources: blazars. This class of AGNs shows a double-bumped spectral energy distribution that is commonly described in…

High Energy Astrophysical Phenomena · Physics 2020-04-08 E. J. Marchesini , A. Paggi , F. Massaro , N. Masetti , R. D'Abrusco , I. Andruchow , R. de Menezes

The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy \gamma-ray telescope, covering the energy range from 20…

Instrumentation and Methods for Astrophysics · Physics 2015-03-20 LAT Collaboration

Fermi-LAT observations provide continuous and regularly-sampled measurements of gamma-ray photon flux for hundreds of blazars. Many of these light curves, spanning almost 15 years, have been thoroughly examined for periodicity in multiple…

High Energy Astrophysical Phenomena · Physics 2023-09-26 Polina Novikova , Ekaterina Shishkina , Dmitry Blinov

We search through $\gamma$-ray data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope and find 24 blazars (or candidates) that have a single clear flare event in their 9.5 year long-term light curves.…

High Energy Astrophysical Phenomena · Physics 2020-01-08 Gege Wang , Zhongxiang Wang , Liang Chen , Jianeng Zhou , Yi Xing

We present a systematic reassessment of 5,062 high-Galactic latitude gamma-ray sources from the Fermi-LAT 4FGL-DR4 catalog using Firmamento, a web-based platform for multi-frequency source discovery and analysis. Our goal is to provide an…

CTA 102 is a $\gamma$-ray bright blazar that exhibited multiple flares in observations by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope during the period of 2016-2018. We present results from the analysis of…

The Fermi Large Area Telescope (LAT) has been surveying the sky in gamma rays from 30 MeV to more than 300 GeV since August 2008. Fermi is the only mission able to detect high energy > few hundreds MeV emission from the Sun during the new…

High Energy Astrophysical Phenomena · Physics 2019-08-15 G. Iafrate , F. Longo

The Fermi-LAT has observed new gamma-ray flares from the blazar B0218+357 during July 2014. While no significant change in the gamma-ray spectrum has been previously observed through the flaring phase in late-2012, during this recent high…

High Energy Astrophysical Phenomena · Physics 2015-02-12 S. Buson , C. C. Cheung , S. Larsson , J. D. Scargle

We report on long-term multi-wavelength monitoring of blazar Mrk 421 by the GASP-WEBT collaboration and Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by…

High Energy Astrophysical Phenomena · Physics 2019-08-14 M. I. Carnerero , C. M. Raiteri , M. Villata , J. A. Acosta-Pulido , V. M. Larionov , P. S. Smith , F. D'Ammando

We present a search for intraday transient gamma-ray signals using 15.4 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 2024-07-30 D. A. Prokhorov , A. Moraghan

We present the first Fermi Large Area Telescope (LAT) catalog of long-term $\gamma$-ray transient sources (1FLT). This comprises sources that were detected on monthly time intervals during the first decade of Fermi-LAT operations. The…

High Energy Astrophysical Phenomena · Physics 2021-09-29 L. Baldini , J. Ballet , D. Bastieri , J. Becerra Gonzalez , R. Bellazzini , A. Berretta , E. Bissaldi , R. D. Blandford , E. D. Bloom , R. Bonino , E. Bottacini , P. Bruel , S. Buson , R. A. Cameron , P. A. Caraveo , E. Cavazzuti , S. Chen , G. Chiaro , D. Ciangottini , S. Ciprini , P. Cristarella Orestano , M. Crnogorcevic , S. Cutini , F. D'Ammando , P. de la Torre Luque , F. de Palma , S. W. Digel , N. Di Lalla , F. Dirirsa , L. Di Venere , A. Domínguez , A. Fiori , H. Fleischhack , A. Franckowiak , Y. Fukazawa , S. Funk , P. Fusco , F. Gargano , D. Gasparrini , S. Germani , N. Giglietto , F. Giordano , M. Giroletti , D. Green , I. A. Grenier , S. Griffin , S. Guiriec , M. Gustafsson , J. W. Hewitt , D. Horan , R. Imazawa , G. Jóhannesson , M. Kerr , D. Kocevski , M. Kuss , S. Larsson , L. Latronico , J. Li , I. Liodakis , F. Longo , F. Loparco , M. N. Lovellette , P. Lubrano , S. Maldera , A. Manfreda , G. Martí-Devesa , H. Matake , M. N. Mazziotta , I. Mereu , M. Meyer , N. Mirabal , W. Mitthumsiri , T. Mizuno , M. E. Monzani , A. Morselli , I. V. Moskalenko , S. Nagasawa , M. Negro , R. Ojha , M. Orienti , E. Orlando , M. Palatiello , V. Paliya , D. Paneque , Z. Pei , M. Persic , M. Pesce-Rollins , V. Petrosian , H. Poon , T. A. Porter , G. Principe , J. L. Racusin , S. Rainò , R. Rando , B. Rani , M. Razzano , S. Razzaque , A. Reimer , O. Reimer , P. M. Saz Parkinson , L. Scotton , D. Serini , C. Sgrò , E. J. Siskind , G. Spandre , P. Spinelli , D. J. Suson , H. Tajima , D. Tak , D. F. Torres , G. Tosti , E. Troja , K. Wood , M. Yassine , G. Zaharijas

We present the detections of 19 solar flares detected in high-energy gamma rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first four years of operation. Interestingly, all flares are associated with fairly fast…

High Energy Astrophysical Phenomena · Physics 2017-02-22 LAT collaboration

Aims. We use a sample of 83 core-dominated active galactic nuclei (AGN) selected from the MOJAVE (Monitoring of Jets in AGN with VLBA Experiments) radio-flux-limited sample and detected with the Fermi Large Area Telescope (LAT) to study the…

Cosmology and Nongalactic Astrophysics · Physics 2015-05-28 T. G. Arshakian , J. León-Tavares , M. Boettcher , J. Torrealba , V. H. Chavushyan , M. L. Lister , E. Ros , J. A. Zensus

The extensive observations done by the X-ray telescope onboard Neil Gehrels Swift observatory has revealed the presence of late time flares concurrent with the decaying afterglow emission. However, the origin of these flares are elusive. In…

High Energy Astrophysical Phenomena · Physics 2023-09-15 Joseph Saji , Shabnam Iyyani , Kratika Mazde