scholarly journals A search for Centaurus A-like features in the spectra of Fermi-LAT detected radio galaxies

2020 ◽  
Vol 492 (4) ◽  
pp. 4666-4679 ◽  
Author(s):  
Cameron B Rulten ◽  
Anthony M Brown ◽  
Paula M Chadwick
Keyword(s):  
Radio Galaxies ◽  
Spectral Energy ◽  
Spectral Features ◽  
Strong Positive Correlation ◽  
Large Area ◽  
Show Evidence ◽  
Simple Extrapolation ◽  
Γ Ray ◽  
5 Ghz ◽  
Centaurus A

ABSTRACT Motivated by the detection of a hardening in the γ-ray spectrum of the radio galaxy Centaurus A, we have analysed $\mathord {\sim }10$ yr of Fermi-Large Area Telescope (LAT) observations of 26 radio galaxies to search for similar spectral features. We find that the majority of the radio galaxies’ γ-ray spectral energy distributions are best fitted with a simple power-law model, and no spectral hardening similar to that found in Centaurus A was detected. We show that, had there been any such spectral features present in our sample of radio galaxies, they would have been seen, but note that seven of the radio galaxies (3C 111, 3C 120, 3C 264, IC 4516, NGC 1218, NGC 2892, and PKS 0625−35) show evidence for flux variability on 6-month time-scales, which makes the detection of any steady spectral features difficult. We find a strong positive correlation (r = 0.9) between the core radio power at 5 GHz and the γ-ray luminosity and, using a simple extrapolation to TeV energies, we expect around half of the radio galaxies studied will be detectable with the forthcoming Cherenkov Telescope Array.

scholarly journals Non-thermal emission in lobes of radio galaxies – III. 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236

2019 ◽  
Vol 491 (4) ◽  
pp. 5740-5746 ◽  
Author(s):  
Massimo Persic ◽  
Yoel Rephaeli
Keyword(s):  
Thermal Emission ◽  
Radio Galaxies ◽  
Spectral Energy ◽  
Large Area ◽  
Microwave Background ◽  
Extragalactic Background Light ◽  
X Ray ◽  
Radiation Fields ◽  
Cygnus A ◽  
Γ Ray

ABSTRACT Recent analyses of the broad spectral energy distributions (SEDs) of extensive lobes of local radio galaxies have confirmed the leptonic origin of their Fermi/Large Area Telescope γ-ray emission, significantly constraining the level of hadronic contribution. SEDs of distant (DL > 125 Mpc) radio-galaxy lobes are currently limited to the radio and X-ray bands, hence give no information on the presence of non-thermal (NT) protons but are adequate to describe the properties of NT electrons. Modelling lobe radio and X-ray emission in 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236, we fully determine the properties of intralobe NT electrons and estimate the level of the related γ-ray emission from Compton scattering of the electrons off the superposed cosmic microwave background, extragalactic background light, and source-specific radiation fields.

scholarly journals Non-thermal emission in radio galaxy lobes – II. Centaurus A, Centaurus B, and NGC 6251

2019 ◽  
Vol 490 (2) ◽  
pp. 1489-1497 ◽  
Author(s):  
Massimo Persic ◽  
Yoel Rephaeli
Keyword(s):  
Thermal Emission ◽  
Background Radiation ◽  
Spectral Energy Distribution ◽  
Recent Analysis ◽  
Spectral Energy ◽  
Energetic Proton ◽  
X Ray ◽  
Radiation Fields ◽  
Γ Ray ◽  
Centaurus A

ABSTRACT Radio and γ-ray measurements of large lobes of several radio galaxies provide adequate basis for determining whether emission in these widely separated spectral regions is largely by energetic electrons. This is very much of interest as there is of yet no unequivocal evidence for a significant energetic proton component to account for γ-ray emission by neutral pion decay. A quantitative assessment of the pion yield spectral distribution necessitates full accounting of the local and background radiation fields in the lobes; indeed, doing so in our recent analysis of the spectral energy distribution of the Fornax A lobes considerably weakened previous conclusions on the hadronic origin of the emission measured by the Fermi satellite. We present the results of similar analyses of the measured radio, X-ray, and γ-ray emission from the lobes of Centaurus A, Centaurus B, and NGC 6251. The results indicate that the measured γ-ray emission from these lobes can be accounted for by Compton scattering of the radio-emitting electrons off the superposed radiation fields in the lobes; consequently, we set upper bounds on the energetic proton contents of the lobes.

scholarly journals Extreme and high synchrotron peak blazars beyond 4FGL: The 2BIGB γ-ray catalogue

2020 ◽  
Vol 493 (2) ◽  
pp. 2438-2451
Author(s):  
B Arsioli ◽  
Y-L Chang ◽  
B Musiimenta
Keyword(s):  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
High Energy ◽  
Spectral Energy ◽  
Large Area ◽  
Data Repositories ◽  
Total Contribution ◽  
Public Data ◽  
Γ Ray

ABSTRACT This paper presents the results of a γ-ray likelihood analysis over all the extreme and high synchrotron peak blazars (EHSP and HSP) from the 3HSP catalogue. We investigate 2013 multifrequency positions under the eyes of Fermi Large Area Telescope, considering 11 yr of observations in the energy range between 500 MeV and 500 GeV, which results in 1160 γ-ray signatures detected down to the TS=9 threshold. The detections include 235 additional sources concerning the Fermi Large Area Telescope Fourth Source Catalog (4FGL), all confirmed via high-energy TS (Test Statistic) maps, and represent an improvement of ∼25 per cent for the number of EHSP and HSP currently described in γ-rays. We build the γ-ray spectral energy distribution (SED) for all the 1160 2BIGB sources, plot the corresponding γ-ray logN−logS, and measure their total contribution to the extragalactic gamma-ray background, which reaches up to ∼33 per cent at 100 GeV. Also, we show that the γ-ray detectability improves according to the synchrotron peak flux as represented by the figure of merit parameter, and note that the search for TeV peaked blazars may benefit from considering HSP and EHSP as a whole, instead of EHSPs only. The 2BIGB acronym stands for ‘Second Brazil-ICRANet Gamma-ray Blazars’ catalogue, and all the broad-band models and SED data points will be available on public data repositories (OpenUniverse, GitHub, and Brazilian Science Data Center-BSDC).

scholarly journals FERMI LAT OBSERVATION OF CENTAURUS A RADIO GALAXY

2013 ◽  
Vol 23 ◽  
pp. 27-33
Author(s):  
N. V. SAHAKYAN
Keyword(s):  
Gamma Ray ◽  
Radio Galaxy ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Large Area ◽  
Radio Image ◽  
Likelihood Analysis ◽  
Low Energies ◽  
Photon Index ◽  
Centaurus A

The results of analysis of approximately 3 year gamma-ray observations (August 2008–July 2011) of the core of radio galaxy Centaurus A with the Fermi Large Area Telescope (Fermi LAT) are presented. Binned likelihood analysis method applying to the data shows that below several GeV the spectrum can be described by a single power-law with photon index Γ = 2.73 ± 0.06. However, at higher energies the new data show significant excess above the extrapolation of the energy spectrum from low energies. The comparison of the corresponding Spectral Energy Distribution (SED) at GeV energies with the SED in the TeV energy band reported by the H.E.S.S. collaboration shows that we deal with two or perhaps even three components of gamma-radiation originating from different regions located within the central 10 kpc of Centaurus A. The analysis of gamma-ray data of Centaurus A lobe accumulated from the beginning of the operation until November 14, 2011 show extension of the HE gamma-ray emission beyond the WMAP radio image in the case of the Northern lobe [9]. The possible origins of gamma-rays from giant radio lobes of Centaurus A are discussed in the context of hadronic and leptonic scenarios.

X-ray and γ-ray emissions from NLSy1 galaxies

2018 ◽  
Vol 27 (10) ◽  
pp. 1844001 ◽  
Author(s):  
V. Baghmanyan ◽  
N. Sahakyan
Keyword(s):  
Spectral Properties ◽  
Radio Galaxies ◽  
Narrow Line ◽  
High Luminosity ◽  
Large Area ◽  
X Ray ◽  
Emission Properties ◽  
Balmer Lines ◽  
Γ Ray

The recent observations by Fermi large area telescope (Fermi-LAT) showed that in addition to the radio galaxies and blazars, Narrow-Line Seyfert 1 (NLSy1) galaxies are also [Formula: see text]-rays emitters. NLSy1 are AGNs with optical spectral properties similar to those of Seyfert 1 galaxies, except for having narrow Balmer lines and strong optical lines. They also exhibit strong X-ray variability, steep X-ray spectra and relatively high luminosity. The multiwavelength emission properties of 1H 0323+342, SBS 0846+513 and PMN J0948+0022 are discussed, using the [Formula: see text]-ray data from the last 8.8 years Fermi-LAT observations as well as available Swift(UVOT/XRT) data. It is shown that one-zone synchrotron/synchrotron self-Compton (SSC) model can satisfactorily reproduce their observed broadband spectra.

scholarly journals X-ray and γ-ray orbital variability from the γ-ray binary HESS J1832−093

2020 ◽  
Vol 637 ◽  
pp. A23 ◽  
Author(s):  
G. Martí-Devesa ◽  
O. Reimer
Keyword(s):  
Energy Distribution ◽  
Massive Star ◽  
Spectral Energy Distribution ◽  
Compact Object ◽  
Spectral Energy ◽  
Large Area ◽  
Optical Telescope ◽  
X Ray ◽  
Orbital Modulation ◽  
Γ Ray

Context.γ-ray binaries are systems composed of a massive star and a compact object whose interaction leads to particle acceleration up to relativistic energies. In the last fifteen years, a few binaries have been found to emit at high energies, but their number is still low. The TeV source HESS J1832−093 has been proposed as a binary candidate, although its nature is unclear. Neither a GeV counterpart nor a period was detected. Aims. The purpose of this work is to search for a GeV counterpart to understand the origin of the TeV signal detected by H.E.S.S. For an unambiguous identification of its binary nature, finding an orbital modulation is crucial. Methods. We analysed data spanning more than 10 years from the Fermi Large Area Telescope (Fermi-LAT), together with Swift archival observations taken between 2015 and 2018, using both the X-Ray Telescope and UV/Optical Telescope. We searched for periodicities in both X-ray and GeV bands. Results. We find a periodic modulation of ∼ 86 days in the X-ray source candidate counterpart XMMU J183245−0921539, together with indications of γ-ray modulation with a compatible period in the GeV candidate counterpart 4FGL J1832.9−0913. Neither an optical nor a UV counterpart is found at the X-ray source location. The overall spectral energy distribution strongly resembles the known γ-ray binary HESS J0632+057. Conclusions. Both the spectral energy distribution and the discovery of an orbital period allow the identification of the TeV source HESS J1832−093 as a new member of the γ-ray binary class.

Multiwavelength study of different flaring and low-activity states of blazar 4C+21.35

2020 ◽  
Vol 500 (1) ◽  
pp. 1127-1138
Author(s):  
Debbijoy Bhattacharya ◽  
Krishna Mohana A ◽  
Subir Bhattacharyya ◽  
Nilay Bhatt ◽  
C S Stalin
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
Optical Data ◽  
Spectral Energy ◽  
Emission Region ◽  
Electromagnetic Spectrum ◽  
Large Area ◽  
Γ Ray ◽  
The One ◽  
Low Activity

ABSTRACT Blazars, a class of active galactic nuclei, emit over the entire accessible electromagnetic spectrum and modelling of their broad-band spectral energy distribution (SED) is the key to constrain the underlying emission mechanisms. Here we report the results on the one-zone leptonic emission modelling carried out on the blazar 4C+21.35 using multiwavelength data spanning over the period 2008–2018. Broad-band SED modelling using γ-ray data from Fermi-Large Area Telescope, X-ray data from Swift-XRT and AstroSat, and UV–optical data from Swift-UVOT, AstroSat, and Catalina Real-Time Transient Survey was carried out at seven different epochs, including three γ-ray flaring episodes and four quiescent periods (three long-term averaged ones and one during AstroSat observing period). Our SED modelling suggests that two compact emission regions originating at a different time outside the broad-line region and moving away from the core with variation primarily in the jet electron spectra can explain the emission from the high-, moderate-, and low-activity periods. The emissions from high- and first low-activity states are likely to have originated in the first region. The moderate- and second low-activity states are likely due to the second emission region with fresh particle acceleration/injection at a later time.

scholarly journals The coordinated radio and infrared survey for high-mass star formation

2018 ◽  
Vol 615 ◽  
pp. A103 ◽  
Author(s):  
I. E. Kalcheva ◽  
M. G. Hoare ◽  
J. S. Urquhart ◽  
S. Kurtz ◽  
S. L. Lumsden ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Plane ◽  
High Mass ◽  
Spectral Energy ◽  
Mass Star ◽  
Large Area ◽  
Massive Star Formation ◽  
Extended Source ◽  
5 Ghz

A catalogue of 239 ultra-compact H II  regions (UCHIIs) found in the CORNISH survey at 5 GHz and 1.5″ resolution in the region 10° < l < 65°,  |b| < 1° is presented. This is the largest complete and well-selected sample of UCHIIs to date and provides the opportunity to explore the global and individual properties of this key state in massive star formation at multiple wavelengths. The nature of the candidates was validated, based on observational properties and calculated spectral indices, and the analysis is presented in this work. The physical sizes, luminosities and other physical properties were computed by utilising literature distances or calculating the distances whenever a value was not available. The near- and mid-infrared extended source fluxes were measured and the extinctions towards the UCHIIs were computed. The new results were combined with available data at longer wavelengths and the spectral energy distributions (SEDs) were reconstructed for 177 UCHIIs. The bolometric luminosities obtained from SED fitting are presented. By comparing the radio flux densities to previous observational epochs, we find about 5% of the sources appear to be time variable. This first high-resolution area survey of the Galactic plane shows that the total number of UCHIIs in the Galaxy is ~750 – a factor of 3–4 fewer than found in previous large area radio surveys. It will form the basis for future tests of models of massive star formation.

scholarly journals Gamma-ray observations of low-luminosity active galactic nuclei

2020 ◽  
Vol 492 (3) ◽  
pp. 4120-4130 ◽  
Author(s):  
Raniere de Menezes ◽  
Rodrigo Nemmen ◽  
Justin D Finke ◽  
Ivan Almeida ◽  
Bindu Rani
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Detailed Comparison ◽  
Spectral Energy ◽  
X Rays ◽  
Large Area ◽  
Accretion Flow ◽  
Γ Rays ◽  
Γ Ray

ABSTRACT The majority of the activity around nearby (z ≈ 0) supermassive black holes is found in low-luminosity active galactic nuclei (LLAGN), the most of them being classified as low-ionization nuclear emission regions. Although these sources are well studied from radio up to X-rays, they are poorly understood in γ-rays. In this work, we take advantage of the all sky-surveying capabilities of the Large Area Telescope on board Fermi Gamma-ray Space Telescope to study the whole Palomar sample of LLAGN in γ-rays. Precisely, the four radio-brightest LLAGN in the sample are identified as significant γ-ray emitters, all of which are recognized as powerful Fanaroff–Riley I galaxies. These results suggest that the presence of powerful radio jets is of substantial importance for observing a significant γ-ray counterpart even if these jets are misaligned with respect to the line of sight. We also find that most of the X-ray-brightest LLAGN do not have a significant γ-ray and strong radio emission, suggesting that the X-rays come mainly from the accretion flow in these cases. A detailed analysis of the spectral energy distributions (SEDs) of NGC 315 and NGC 4261, both detected in γ-rays, is provided where we make a detailed comparison between the predicted hadronic γ-ray emission from a radiatively inefficient accretion flow (RIAF) and the γ-ray emission from a leptonic jet-dominated synchrotron self-Compton (SSC) model. Both SEDs are better described by the SSC model, while the RIAF fails to explain the γ-ray observations.

scholarly journals A search for γ-ray emission from a sample of local Universe low-frequency selected radio galaxies

2020 ◽  
Vol 496 (1) ◽  
pp. 903-912
Author(s):  
Max Harvey ◽  
Cameron B Rulten ◽  
Paula M Chadwick
Keyword(s):  
Low Frequency ◽  
Radio Galaxies ◽  
Large Area ◽  
Complete Sample ◽  
Local Universe ◽  
The Earth ◽  
Upper Limits ◽  
Γ Ray ◽  
The Look ◽  
Large Parameter Space

ABSTRACT Radio galaxies are uncommon γ-ray emitters, and only low-redshift radio galaxies are detected with the Fermi Large Area Telescope (Fermi-LAT). However, they offer potential insights into the emission mechanisms of active galaxies, particularly as the alignment of their jets with respect to the Earth means that, unlike blazars, their emission is not necessarily jet dominated. We use the Fermi-LAT data to perform an unbiased survey of 78 radio galaxies from the Bologna complete sample in order to search for new γ-ray-emitting radio galaxies. We observe statistically significant γ-ray emission from four of the six known Fermi-LAT-detected radio galaxies included in this sample, and find some evidence for γ-ray emission spatially coincident with four previously undetected radio galaxies. As a large parameter space is searched, we calculate a probability distribution to compute the look-elsewhere effect. We find that these four spatially coincident sub-threshold γ-ray excesses are most likely a chance association, and are unlikely to be emission from the radio galaxies. Upper limits on flux are calculated for the radio galaxies from which no γ-ray emission is observed.

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