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In 1989, an air-borne experiments (VEGA experiment) aiming at the detection of a few 10 GeV $\gamma$-ray were carried out. In these experiments, nine point-source candidates along the Galactic plane were reported. In these candidates, the…

Astrophysics · Physics 2007-05-23 Ryoji Enomoto

Recent observations with atmospheric Cherenkov telescope systems such as H.E.S.S. and MAGIC have revealed a large number of new sources of very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated along the Galactic…

Astrophysics · Physics 2008-11-26 S. Funk , O. Reimer , D. F. Torres , J. A. Hinton

A comprehensive search for variable and transient radio sources has been conducted using ~55,000 snapshot images of the FIRST survey. We present an analysis leading to the discovery of 1,627 variable and transient objects down to mJy levels…

Cosmology and Nongalactic Astrophysics · Physics 2015-05-30 Nithyanandan Thyagarajan , David J. Helfand , Richard L. White , Robert H. Becker

For the duration of the Fermi Gamma-Ray Space Telescope's mission, approximately one-third of the point sources detected have been noted as "unassociated," meaning that they seem to have no known counterpart at any other…

High Energy Astrophysical Phenomena · Physics 2021-08-11 S. Bruzewski , F. K. Schinzel , G. B. Taylor , L. Petrov

We present a low-frequency imaging study of an extended sample of X-shaped radio sources using the Giant Metrewave radio telescope (GMRT) at two frequencies (610 and 240 MHz). The sources were drawn from a Very Large Array FIRST-selected…

Astrophysics of Galaxies · Physics 2019-05-08 Dharam V. Lal , Biny Sebastian , C. C. Cheung , A. Pramesh Rao

B2013+370 and B2023+336 are two blazars at low-galactic latitude that were previously proposed to be the counterparts for the EGRET unidentified sources, 3EG J2016+3657 and 3EG J2027+3429. Gamma-ray emission associated with the EGRET…

High Energy Astrophysical Phenomena · Physics 2015-06-03 E. Kara , M. Errando , W. Max-Moerbeck , E. Aliu , M. Bottcher , P. Fortin , J. P. Halpern , R. Mukherjee , A. C. S. Readhead , J. L. Richards

This paper presents results of a survey search for bright compact radio sources at 22 GHz with the VERA radio-interferometer. Each source from a list of 2494 objects was observed in one scan for 2 minutes. The purpose of this survey was to…

Astrophysics · Physics 2008-11-26 L. Petrov , T. Hirota , M. Honma , K. M. Shibata , T. Jike , H. Kobayashi

We recently identified the blazar-like radio source G74.87+1.22 (B2013+370) as the counterpart of the high-energy gamma-ray source 3EG J2016+3657 in the Galactic plane. However, since most blazar identifications of EGRET sources are only…

Astrophysics · Physics 2009-10-31 J. P. Halpern , M. Eracleous , R. Mukherjee , E. V. Gotthelf

The radio spectral index is a powerful probe for classifying cosmic radio sources and understanding the origin of the radio emission. Combining data at 147 MHz and 1.4 GHz from the TIFR GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey…

Instrumentation and Methods for Astrophysics · Physics 2018-01-10 F. de Gasperin , H. T. Intema , D. A. Frail

The limited angular resolution of gamma-ray telescopes prevents a direct identification of the majority of sources detected so far. This is particularly true for the low latitude, probably galactic, ones only 10 % of which has been…

The third EGRET catalog contains a large number of unidentified sources. This subset of objects is expected to include known gamma-ray emitters of Galactic origin such as pulsars and supernova remnants, in addition to an extragalactic…

Astrophysics · Physics 2009-03-26 J. M. Siegal-Gaskins , V. Pavlidou , A. V. Olinto , C. Brown , B. D. Fields

A brief summary of the main properties of the unidentified gamma-ray sources detected by EGRET is presented, with particular emphasis on the different populations and their phenomenological characteristics.

Astrophysics · Physics 2016-11-09 G. E. Romero

A significant fraction (~30%) of the high-energy gamma-ray sources listed in the second Fermi LAT catalog (2FGL) are still of unknown origin, being not yet associated with counterparts at low energies. We recently developed a new…

High Energy Astrophysical Phenomena · Physics 2015-06-15 F. Massaro , R. D'Abrusco , A. Paggi , N. Masetti , M. Giroletti , G. Tosti , Howard A. Smith , S. Funk

Starting in 1991 we have performed a regular monitoring of EGRET sources with the Effelsberg 100-m telescope and the IRAM 30-m at Pico Veleta. In comparison with data on a sample of flat-spectrum quasars which have not been seen by EGRET we…

Astrophysics · Physics 2007-05-23 M. Pohl , A. Muecke , W. Reich , P. Reich , R. Schlickeiser , H. Ungerechts

Gigahertz-Peaked spectrum (GPS) sources are compact active galactic nuclei, presumably young precursors of bright radio sources. The study of GPS radio properties provides information about the features of synchrotron radiation in…

Astrophysics of Galaxies · Physics 2020-01-08 Yu. Sotnikova , T. Mufakharov , E. Majorova , M. Mingaliev , R. Udovitskiy , N. Bursov , T. Semenova

Blazars are a highly-variable, radio-loud subclass of active galactic nuclei (AGN). In order to better understand such objects we must be able to easily identify candidate blazars from the growing population of unidentified sources. Working…

High Energy Astrophysical Phenomena · Physics 2015-06-16 Philip S. Cowperthwaite , F. Massaro , R. D'Abrusco , A. Paggi , G. Tosti , Howard A. Smith

The INTEGRAL satellite has been observing the gamma-ray sky for 15 years and has detected over 900 X-ray sources of various nature. However, more than 200 of these sources still lack precise identification. Our goal is to reveal the nature…

High Energy Astrophysical Phenomena · Physics 2018-10-31 Francis Fortin , Sylvain Chaty , Alexis Coleiro , John Tomsick , Christian Nitschelm

Spectral variability of radio sources encodes information about the conditions of intervening media, source structure, and emission processes. With new low-frequency radio interferometers observing over wide fractional bandwidths, studies…

Astrophysics of Galaxies · Physics 2020-12-23 K. Ross , J. R. Callingham , N. Hurley-Walker , N. Seymour , P. Hancock , T. M. O. Franzen , J. Morgan , S. V. White , M. E. Bell , P. Patil

Microquasars are X-ray binaries with relativistic jets. The microquasar LS 5039 turned out to be the first high-energy gamma-ray microquasar candidate due to its likely association with the EGRET source 3EG J1824-1514. Further theoretical…

Astrophysics · Physics 2015-06-24 V. Bosch-Ramon , J. M. Paredes , G. E. Romero

We compute the variation of the beaming fraction with the efficiency of high energy gamma-ray production in the outer gap pulsar model of Romani and Yadigaroglu. This allows us to correct the fluxes observed for pulsars in the EGRET band…

Astrophysics · Physics 2009-10-22 I. -A. Yadigaroglu , Roger W. Romani
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