scholarly journals Modelling the Multifrequency SED of AGN Candidates among the Unidentied EGRET and Fermi Gamma-Ray Sources

2014 ◽  
Vol 1 (1) ◽  
pp. 163-169
Author(s):  
Pieter J. Meintjes ◽  
Pheneas Nkundabakura ◽  
Brian Van Soelen ◽  
Alida Odendaal
Keyword(s):  
Gamma Ray ◽  
Radio Galaxy ◽  
Radio Galaxies ◽  
Galactic Latitude ◽  
Large Telescope ◽  
High Galactic Latitude ◽  
New Class ◽  
Multi Wavelength ◽  
One Year

Of the 271 sources in the 3rd EGRET catalogue, 131 were reported as unidentied, i.e. not associated with any particular class of point source in the sky. Since the largest fraction of the EGRET sources were extragalactic, a sample of 13 extragalactic unidentied sources have been selected for multi-wavelength follow-up studies. Five of the selected EGRET sources coincide with gamma-ray flux enhancements seen in the Fermi-LAT data after one year of operation. In this article, we report the multi-wavelength properties of, among others, the 5 sources detected by Fermi-LAT from our sample of high galactic latitude unidentied EGRET sources. Recent spectroscopic observations with the Southern African Large Telescope (SALT) conrmed one of the unidentied EGRET sources as a possible Seyfert 2 galaxy, or alternatively, a narrow line radio galaxy. The detected gamma-ray emission (E<sub>γ</sub> &gt; 30 MeV) of the 5 coinciding EGRET/Fermi-LAT sources are tted with external Compton and Synchrotron Self Compton (SSC) models to investigate the energetics required to produce the EGRET/Fermi gamma-ray flux. In all the models the inclination angle of the jet with respect to the observer is jet 60, between those of Seyfert 1 and Seyfert 2/radio galaxies. These results confirm the possibility of Seyfert and radio galaxies sources are constituting a new class of gamma-ray source in the energy range E<sub>γ</sub> &gt; 30 MeV.

scholarly journals Gamma-ray emission in radio galaxies under the VLBI scope

2019 ◽  
Vol 627 ◽  
pp. A148 ◽  
Author(s):  
R. Angioni ◽  
E. Ros ◽  
M. Kadler ◽  
R. Ojha ◽  
C. Müller ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Monitoring Program ◽  
Radio Galaxies ◽  
High Energy ◽  
Viewing Angle ◽  
Long Baseline ◽  
Superluminal Motion ◽  
Multi Wavelength ◽  
The Individual ◽  
The Relationship

Aims. In the framework of the multi-wavelength and very long baseline interferometry (VLBI) monitoring program TANAMI (Tracking Active Nuclei with Austral Milliarcsecond Interferometry), we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the γ-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. Methods. The TANAMI program monitors a large sample of radio-loud AGN at 8.4 GHz and 22.3 GHz with the Australian long baseline array (LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We performed a kinematic analysis for five γ-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed 103 months of Fermi-LAT data in order to study possible connections between the γ-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey, with a total of fifteen sources. Results. We find that the first γ-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. We detect subluminal parsec-scale jet motions in the peculiar AGN PKS 0521−36, and we confirm the presence of fast γ-ray variability in the source down to timescales of six hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to βapp ∼ 3, in the jet of the TeV radio galaxy PKS 0625−35. Our VLBI results constrain the jet viewing angle to be θ <  53°, allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical compact symmetric object (CSO) PKS 1718−649, we place an upper limit on the separation speed between the two mini-lobes. This in turn allows us to derive a lower limit on the age of the source. Conclusions. We can draw some preliminary conclusions on the relationship between pc-scale jets and γ-ray emission in radio galaxies, based on Fermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the γ-ray flux, as seen in blazars. On the other hand, the γ-ray luminosity does not show any dependence on the core brightness temperature and core dominance, which are two common indicators of jet Doppler boosting. This seems to indicate that γ-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, in accordance with the unified model of jetted AGN.

scholarly journals Gamma-ray emission in radio galaxies, from MeV to TeV

2018 ◽  
Vol 14 (S342) ◽  
pp. 158-166
Author(s):  
Eleonora Torresi
Keyword(s):  
Gamma Ray ◽  
Radio Galaxies ◽  
High Energy ◽  
Cherenkov Telescopes ◽  
New Class ◽  
Very High Energy ◽  
Structure Complexity ◽  
The Impact ◽  
Jet Structure ◽  
Very High

AbstractThanks to the Fermi λ-ray satellite and the current Imaging Atmospheric Cherenkov Telescopes, radio galaxies have arisen as a new class of high- and very-high energy emitters. The favourable orientation of their jets makes radio galaxies extremely relevant in addressing important issues such as: (i) revealing the jet structure complexity; (ii) localising the emitting region(s) of high- and very-high energy radiation; (iii) understanding the physical processes producing these photons. In this review the main results on the λ-ray emission studies of radio galaxies from the MeV to TeV regimes will be presented, and the impact of future Cherenkov Telescope Array observations will be discussed.

scholarly journals Radio Galaxies - The TeV Challenge

2018 ◽  
Author(s):  
Bindu Rani
Keyword(s):  
Gamma Ray ◽  
Radio Galaxies ◽  
High Energy ◽  
Energy Emission ◽  
Long Baseline ◽  
Multi Wavelength ◽  
Emission Models ◽  
Radiation Processes ◽  
High Energy Emission ◽  
Near Future

Over the past decade, our knowledge of the $\gamma$-ray sky has been revolutionized by ground- and space-based observatories by detecting photons up to several hundreds of tera-electron volt (TeV) energies. A major population of the $\gamma$-ray bright objects are active galactic nuclei (AGN) with their relativistic jets pointed along our line-of-sight. Gamma-ray emission is also detected from nearby mis-aligned AGN such as radio galaxies. While the TeV-detected radio galaxies ($TeVRad$) only form a small fraction of the $\gamma$-ray detected AGN, their multi-wavelength study offers a unique opportunity to probe and pinpoint the high-energy emission processes and sites. Even in the absence of substantial Doppler beaming $TeVRad$ are extremely bright objects in the TeV sky (luminosities detected up to $10^{45}~erg~s^{-1}$), and exhibit flux variations on timescales shorter than the event-horizon scales (flux doubling timescale less than 5 minutes). Thanks to the recent advancement in the imaging capabilities of high-resolution radio interferometry (millimeter very long baseline interferometry, mm-VLBI), one can probe the scales down to less than 10 gravitational radii in $TeVRad$, making it possible not only to test jet launching models but also to pinpoint the high-energy emission sites and to unravel the emission mechanisms. This review provides an overview of the high-energy observations of $TeVRad$ with a focus on the emitting sites and radiation processes. Some recent approaches in simulations are also sketched. Observations by the near-future facilities like Cherenkov Telescope Array, short millimeter-VLBI, and high-energy polarimetry instruments will be crucial for discriminating the competing high-energy emission models.

X-Ray Astronomy

1969 ◽  
Vol 13 ◽  
pp. 289-312
Author(s):  
Herbert Friedman
Keyword(s):  
Radio Galaxy ◽  
Galactic Plane ◽  
Background Radiation ◽  
Galactic Latitude ◽  
Intergalactic Gas ◽  
High Galactic Latitude ◽  
X Ray ◽  
Diffuse Background ◽  
Distant Radio Galaxy ◽  
Radio Power

Although searches so far have been restricted to a few small rockets and balloons, some 40 discrete x-ray sources have already been resolved against a diffuse, nearly isotropic background radiation. The strongest source is about 2000 times as bright as the weakest detectable with present rocket instruments. Nearly all of the discrete sources lie close to the galactic plane and most likely are members of the spiral arms of the Milky Way. One x-ray source at high galactic latitude is identifiable with a distant radio galaxy, Virgo A, and its x-ray luminosity is 70 times its radio power. The diffuse background radiation seems to be resolvable into at least two components: one may be associated with the interaction of cosmic rays and the microwave photons of the cosmological 3 K background; the other with bremsstrahlung from hot, intergalactic gas.

scholarly journals Monitoring and Multi-Messenger Astronomy with IceCube

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 40
Author(s):  
René Reimann
Keyword(s):  
Gamma Ray ◽  
Neutrino Flux ◽  
High Energy ◽  
Observation Window ◽  
Large Program ◽  
Astrophysical Neutrinos ◽  
Multi Wavelength ◽  
Very High Energy ◽  
Scientific Results

IceCube currently is the largest neutrino observatory with an instrumented detection volume of 1 km3 buried in the ice-sheet close to the antarctic South Pole station. With a 4 π field of view and an up-time of >99%, it is continuously monitoring the full sky to detect astrophysical neutrinos. With the detection of an astrophysical neutrino flux in 2013, IceCube opened a new observation window to the non-thermal Universe. The IceCube collaboration has a large program to search for astrophysical neutrinos, including measurements of the energy spectrum of the diffuse astrophysical flux, auto- and cross-correlation studies with other multi-messenger particles, and a real-time alert and follow-up system. On 22 September 2017, the IceCube online system sent out an alert reporting a high-energy neutrino event. This alert triggered a series of multi-wavelength follow-up observations that revealed a spatially-coincident blazar TXS 0506+056, which was also in an active flaring state. This correlation was estimated at a 3 σ level. Further observations confirmed the flaring emission in the very-high-energy gamma-ray band. In addition, IceCube found an independent 3.5 σ excess of a time-variable neutrino flux in the direction of TXS 0506+056 two years prior to the alert by examining 9.5 years of archival neutrino data. These are the first multi-messenger observations of an extra-galactic astrophysical source including neutrinos since the observation of the supernova SN1987A. This review summarizes the different detection and analysis channels for astrophysical neutrinos in IceCube, focusing on the multi-messenger program of IceCube and its major scientific results.

scholarly journals THE SEARCH FOR BLAZARS AMONG THE UNIDENTIFIED EGRET gamma-RAY SOURCES

2013 ◽  
Vol 53 (A) ◽  
pp. 631-634
Author(s):  
Pieter J. Meintjes ◽  
Pheneas Nkundabakura
Keyword(s):  
Gamma Ray ◽  
Spectral Indices ◽  
Optical Photometry ◽  
Follow Up Study ◽  
Spectrum Radio ◽  
Multi Wavelength ◽  
The Mean ◽  
Bl Lacs ◽  
Radio Quasar

In this paper we report the results of a multi-wavelength follow-up study of selected flat spectrum extragalactic radio-optical counterparts within the error boxes of 13 unidentified EGRET sources. Two of these previously unidentified counterparts have been selected for optical photometric and spectroscopic follow-up studies. Spectroscopic observations made with the 4.1m SOAR telescope at Cerro Pachón, Chile, showed that the spectra of the optical counterparts of 3EG J0821−5814 (PKS J0820−5705) and 3EG J0706−3837 (PMN J0710−3835) correspond to a flat spectrum radio quasar (FSRQ) and LINER-Seyfert I galaxy respectively. Optical photometry of these sources, performed with the 1.0m telescope at Sutherland (South-Africa) shows noticeable intranight variability for PKS J0820−5705, as well as a 5 sigma variation of the mean brightness in the R-filter over a timescale of three nights. Significant variability has been detected in the B-band for PMN J0710−3835 as well. The gamma-ray spectral indices of all 13 candidates range between 2–3, correlating well with the BL Lacs and FSRQs detected with Fermi-LAT in the first 11 months of operation.

M 87 — TEN YEARS OF TEV GAMMA-RAY OBSERVATIONS

2010 ◽  
Vol 19 (06) ◽  
pp. 849-857
Author(s):  
MATTHIAS BEILICKE
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Radio Galaxy ◽  
Galactic Nuclei ◽  
Plasma Jet ◽  
Radio Galaxies ◽  
Jet Physics ◽  
X Ray ◽  
High Energies ◽  
Very High

The giant radio galaxy M 87 is located 16.7 Mpc away and harbours a supermassive black hole in its center. Structures of its relativistic plasma jet are resolved at radio, optical and X–ray energies. M 87 belongs to the class of active galactic nuclei and is one of only a few radio galaxies detected at very-high energies (E > 100 GeV ). This makes it a unique laboratory to study jet physics and the corresponding emission processes. The results obtained from TeV gamma-ray observations during the last decade are discussed.

scholarly journals Discovery of Rare Dying Radio Galaxies Using MeerKAT

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 102
Author(s):  
Nadeem Oozeer ◽  
Lawrence Rudnick ◽  
Michael F. Bietenholz ◽  
Tiziana Venturi ◽  
Kenda Knowles ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Radio Galaxy ◽  
Galaxy Cluster ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Central Black Hole ◽  
Massive Galaxies ◽  
Multi Wavelength ◽  
Radio Power

Dying radio galaxies represent a stage of the evolution of active galactic nuclei (AGN), during which the accreting central black hole has switched off and/or falls to such a low level that the plasma outflow can no longer be sustained. When this happens, the radio source undergoes a period of fading, the dying phase, before it disappears completely. We present the study of three potential dying radio sources using the MeerKAT radio telescope: MKT J072851.2-752743, MKT J001940.4-654722, and ACO 548B. The identification as dying radio sources came from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). We carry out a multi-wavelength analysis of the sources and derive their energetics. The ages of the sources are ∼30–70 Myr, they have magnetic fields of the order of a few μG, and they have relatively low radio power. Their potential optical counterparts are associated with massive galaxies. We show that ACO 548B, previously classified as two peripheral relic radio sources, is a dying radio galaxy. With its good sensitivity and resolution, MeerKAT is an ideal instrument to detect potential dying radio sources, and contribute to the understanding of the evolution of AGN population.

scholarly journals The SVOM Mission

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 113
Author(s):  
Maria Grazia Bernardini ◽  
Bertrand Cordier ◽  
Jianyan Wei
Keyword(s):  
Time Domain ◽  
Crucial Role ◽  
Gamma Ray ◽  
Complete Coverage ◽  
Gamma Ray Burst ◽  
Multi Wavelength ◽  
Working Together

SVOM (Space-based multiband astronomical Variable Objects Monitor) is a sino-french mission that is dedicated to Gamma-Ray Burst (GRB) science, expected to be launched in mid 2023. The mission includes four space-based and three ground-based instruments that, working together, will discover GRBs and provide rapid multi-wavelength follow-up in order to obtain a complete coverage of the GRB emission over seven decades in energy, from the trigger up to the very late phases of the afterglow. Thanks to its characteristics, SVOM will play a crucial role in time-domain and multi-messenger astronomy.

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