First Detection in Gamma-Rays of a Young Radio Galaxy: Fermi-Lat Observations of the Compact Symmetric Object PKS 1718−649

Migliori, G.; Siemiginowska, Aneta; Sobolewska, M.; Loh, Alan; Corbel, S.; Ostorero, L.; Stawarz, Ł.

doi:10.3847/2041-8205/821/2/l31

Cited by 58 publications

(68 citation statements)

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“…Similar luminosities are also observed for the extended radio galaxies Centaurus A and M87. However, these two are less distant (z<0.006), as is the other bona fide young radio source detected by Fermi -LAT, NGC 6328 (Migliori et al 2016).…”

Section: Origin Of the γ-Ray Emissionmentioning

confidence: 88%

“…The two sources have similar (low) L γ , linear sizes and dynamically estimated ages. The inner structure of NGC 3894 is as small as ∼ 5 pc and its dynamic age is ∼ 60 years, whereas the estimated linear size and dynamic age of NGC 6328 are ∼ 2 pc and ∼ 100 yr (Migliori et al 2016). This seems to suggest that the detection of CSOs is limited to the closest targets and could be connected to the very first evolutionary stages.…”

Section: Origin Of the γ-Ray Emissionmentioning

confidence: 89%

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NGC 3894: a young radio galaxy seen by Fermi-LAT

Principe

Migliori

Johnson

et al. 2020

A&A

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Context. According to radiative models, radio galaxies may produce γ-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by the Fermi Large Area Telescope (LAT) so far. Aims. NGC 3894 is a nearby (z =0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with a γ-ray counterpart in the Fourth Fermi-LAT source catalog. Here we present a study of the source in the γ-ray and radio bands aimed at investigating its high-energy emission and assess its young nature. Methods. We analyzed 10.8 years of Fermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35 years were used to study the radio morphology of NGC 3894 and its evolution. Results. NGC 3894 is detected in γ-rays with a significance > 9σ over the full period, and no significant variability has been observed in the γ-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law (Γ = 2.0 ± 0.1) and a flux on the order of 2.2 × 10 −9 ph cm−2 s −1 . For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to be βapp,NW = 0.132±0.004 and βapp,SE = 0.065±0.003, respectively. Conclusions. Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59 ± 5 years. The estimated range of viewing angle (10 • < θ < 21 • ) does not exclude a possible jet-like origin of the γ-ray emission.

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Section: Origin Of the γ-Ray Emissionmentioning

confidence: 88%

Section: Origin Of the γ-Ray Emissionmentioning

confidence: 89%

NGC 3894: a young radio galaxy seen by Fermi-LAT

Principe

Migliori

Johnson

et al. 2020

A&A

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“…PMN J1603-4904 adds to the class of so far very rare extragalactic jets that show a spectral turnover in the MHz to GHz range, and are detected at γ-rays. As it is the second confirmed object of this type, following PKS 1718-649 (Migliori et al 2016), there are some noteworthy differences. First, PKS 1718-649 is a nearby galaxy (z = 0.014) in contrast to PMN J1603-4904 at z = 0.23.…”

Section: Discussionmentioning

confidence: 99%

The MHz-peaked radio spectrum of the unusualγ-ray source PMN J1603–4904

Müller

Burd

Schulz

et al. 2016

A&A

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Context. The majority of bright extragalactic γ-ray sources are blazars. Only a few radio galaxies have been detected by Fermi/LAT. Recently, the GHz-peaked spectrum source PKS 1718-649 was confirmed to be γ-ray bright, providing further evidence for the existence of a population of γ-ray loud, compact radio galaxies. A spectral turnover in the radio spectrum in the MHz to GHz range is a characteristic feature of these objects, which are thought to be young due to their small linear sizes. The multiwavelength properties of the γ-ray source PMN J1603-4904 suggest that it is a member of this source class. Aims. The known radio spectrum of PMN J1603-4904 can be described by a power law above 1 GHz. Using observations from the Giant Metrewave Radio Telescope (GMRT) at 150, 325, and 610 MHz, we investigate the behavior of the spectrum at lower frequencies to search for a low-frequency turnover. Methods. Data from the TIFR GMRT Sky Survey (TGSS ADR) catalog and archival GMRT observations were used to construct the first MHz to GHz spectrum of PMN J1603-4904. Results. We detect a low-frequency turnover of the spectrum and measure the peak position at about 490 MHz (rest-frame), which, using the known relation of peak frequency and linear size, translates into a maximum linear source size of ∼1.4 kpc. Conclusions. The detection of the MHz peak indicates that PMN J1603-4904 is part of this population of radio galaxies with turnover frequencies in the MHz to GHz regime. Therefore it can be considered the second confirmed object of this kind detected in γ-rays. Establishing this γ-ray source class will help to investigate the γ-ray production sites and to test broadband emission models.

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“…Finally, the Fermi -LAT detection of a young Compact Symmetric Object (CSO), i.e. PKS 1718-649 (Migliori et al 2016) further supports the non-thermal γ-ray production in the lobes (for a detailed discussion see Migliori 2018, these proceedings).…”

Section: Radio Galaxies Are γ-Ray Emittersmentioning

confidence: 80%

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

Torresi

2018

Proc. IAU

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Thanks to the Fermi γ-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 γ-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.

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First Detection in Gamma-Rays of a Young Radio Galaxy: Fermi-Lat Observations of the Compact Symmetric Object PKS 1718−649

Cited by 58 publications

References 46 publications

NGC 3894: a young radio galaxy seen by Fermi-LAT

NGC 3894: a young radio galaxy seen by Fermi-LAT

The MHz-peaked radio spectrum of the unusualγ-ray source PMN J1603–4904

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

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