scholarly journals The γ-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LAT

2018 ◽  
Vol 619 ◽  
pp. A71 ◽  
Author(s):  
◽  
H. Abdalla ◽  
A. Abramowski ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
...  
Keyword(s):  
Exposure Time ◽  
Statistical Significance ◽  
Spectral Energy Distribution ◽  
Spectral Characteristics ◽  
Physical Nature ◽  
High Energy ◽  
Spectral Energy ◽  
The Core ◽  
Advanced Analysis ◽  
Centaurus A

Centaurus A (Cen A) is the nearest radio galaxy discovered as a very-high-energy (VHE; 100 GeV–100 TeV) γ-ray source by the High Energy Stereoscopic System (H.E.S.S.). It is a faint VHE γ-ray emitter, though its VHE flux exceeds both the extrapolation from early Fermi-LAT observations as well as expectations from a (misaligned) single-zone synchrotron-self Compton (SSC) description. The latter satisfactorily reproduces the emission from Cen A at lower energies up to a few GeV. New observations with H.E.S.S., comparable in exposure time to those previously reported, were performed and eight years of Fermi-LAT data were accumulated to clarify the spectral characteristics of the γ-ray emission from the core of Cen A. The results allow us for the first time to achieve the goal of constructing a representative, contemporaneous γ-ray core spectrum of Cen A over almost five orders of magnitude in energy. Advanced analysis methods, including the template fitting method, allow detection in the VHE range of the core with a statistical significance of 12σ on the basis of 213 hours of total exposure time. The spectrum in the energy range of 250 GeV–6 TeV is compatible with a power-law function with a photon index Γ = 2.52 ± 0.13stat ± 0.20sys. An updated Fermi-LAT analysis provides evidence for spectral hardening by ΔΓ ≃ 0.4 ± 0.1 at γ-ray energies above 2.8+1.0−0.6 GeV at a level of 4.0σ. The fact that the spectrum hardens at GeV energies and extends into the VHE regime disfavour a single-zone SSC interpretation for the overall spectral energy distribution (SED) of the core and is suggestive of a new γ-ray emitting component connecting the high-energy emission above the break energy to the one observed at VHE energies. The absence of significant variability at both GeV and TeV energies does not yet allow disentanglement of the physical nature of this component, though a jet-related origin is possible and a simple two-zone SED model fit is provided to this end.

scholarly journals ON THE GAMMA-RAY EMISSION FROM THE CORE AND RADIO LOBES OF THE RADIO GALAXY CENTAURUS A

2014 ◽  
Vol 28 ◽  
pp. 1460182
Author(s):  
NAREK SAHAKYAN ◽  
FRANK M. RIEGER ◽  
FELIX AHARONIAN ◽  
RUIZHI YANG ◽  
EMMA DE ONA-WILHELMI
Keyword(s):  
Power Law ◽  
Gamma Ray ◽  
Radio Galaxy ◽  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
Radio Image ◽  
The Core ◽  
Gamma Ray Emission ◽  
Centaurus A

We summarize recent results based on an analysis of Fermi-LAT data for the lobes and the core of the nearby radio galaxy Centaurus A (Cen A). In the case of the core, high-energy (HE; > 100 MeV) γ-rays up to 50 GeV have been detected with a detection significance of about 44σ. The average gamma-ray spectrum of the core reveals interesting evidence for a possible deviation from a simple power-law. A likelihood analysis with a broken power-law model shows that the photon index becomes substantially harder above Eb ≃ 4 GeV, changing from Γ1 = 2.74 ± 0.03 below to Γ2 = 2.09 ± 0.20 above. It seems possible that this hardening marks the contribution of an additional high-energy component beyond the common synchrotron-self Compton jet emission. In the case of the lobes, the high-energy gamma-ray emission extends up to 6 GeV, with a significance of more than 10 and 20 σ for the north and the south lobe, respectively. Based on a detailed spatial analysis and comparison with the associated radio lobes, a substantial extension of the HE γ-ray emission beyond the WMAP radio image for the northern lobe of Cen A is found. We provide a short discussion of the lobe's spectral energy distribution (SED) in the context of hadronic and time-dependent leptonic scenarios.

A MODEL FOR THE INNER JET HIGH-ENERGY EMISSION OF CENTAURUS A

2010 ◽  
Vol 19 (06) ◽  
pp. 937-942
Author(s):  
MARIANA ORELLANA ◽  
GUSTAVO E. ROMERO
Keyword(s):  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Meson Production ◽  
High Energy ◽  
Spectral Energy ◽  
Hadronic Interactions ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Great Relevance ◽  
Centaurus A

We investigate the spectral energy distribution (SED) of Centaurus A resulting from a steady compact acceleration region, located close to the central black hole, where both leptonic and hadronic relativistic populations arise. We present here results of such a model, where we have considered synchrotron radiation by primary electrons and protons, inverse Compton scattering, and gamma-ray emission originated by the inelastic hadronic interactions between relativistic protons and cold nuclei within the jets. Photo-meson production by relativistic hadrons were also taken into account, as well as the effects of secondary particles injected by all interactions. The internal and external absorption of gamma-rays is shown to be of great relevance to shape the observable SED, which was also recently constrained by the results of Fermi and HESS.

scholarly journals The TeV-emitting radio galaxy 3C 264

2019 ◽  
Vol 627 ◽  
pp. A89 ◽  
Author(s):  
B. Boccardi ◽  
G. Migliori ◽  
P. Grandi ◽  
E. Torresi ◽  
F. Mertens ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Data Set ◽  
X Ray ◽  
The Core ◽  
Very High Energy ◽  
Acceleration Zone

Context.In March 2018, the detection by VERITAS of very-high-energy emission (VHE >  100 GeV) from 3C 264 was reported. This is the sixth, and second most distant, radio galaxy ever detected in the TeV regime.Aims.In this article we present a radio and X-ray analysis of the jet in 3C 264. We determine the main physical parameters of the parsec-scale flow and explore the implications of the inferred kinematic structure for radiative models of thisγ-ray emitting jet.Methods.The radio data set is comprised of VLBI observations at 15 GHz from the MOJAVE program, and covers a time period of about two years. Through a segmented wavelet decomposition method (WISE code), we estimated the apparent displacement of individual plasma features; we then performed a pixel-based analysis of the stacked image to determine the jet shape. The X-ray data set includes all available observations from theChandra, XMM, andSwiftsatellites, and is used, together with archival data in the other bands, to build the spectral energy distribution (SED).Results.Proper motion is mostly detected along the edges of the flow, which appears strongly limb brightened. The apparent speeds increase as a function of distance from the core up to a maximum of ∼11.5 c. This constrains the jet viewing angle to assume relatively small values (θ ≲ 10°). In the acceleration region, extending up to a de-projected distance of ∼4.8 × 104Schwarzschild radii (∼11 pc), the jet is collimating (r ∝ z0.40 ± 0.04), as predicted for a magnetically-driven plasma flow. By assuming that the core region is indeed magnetically dominated (UB/Ue >  1), the SED and the jet power can be well reproduced in the framework of leptonic models, provided that the high-energy component is associated to a second emitting region. The possibility that this region is located at the end of the acceleration zone, either in the jet layer or in the spine, is explored in the modeling.

scholarly journals Testing emission models on the extreme blazar 2WHSP J073326.7+515354 detected at very high energies with the MAGIC telescopes

2019 ◽  
Vol 490 (2) ◽  
pp. 2284-2299 ◽  
Author(s):  
◽  
◽  
V A Acciari ◽  
S Ansoldi ◽  
L A Antonelli ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Physical Nature ◽  
High Energy ◽  
Spectral Energy ◽  
Emission Model ◽  
Theoretical Frameworks ◽  
Spectral Parameters ◽  
Bl Lac Objects

ABSTRACT Extreme high-energy-peaked BL Lac objects (EHBLs) are an emerging class of blazars. Their typical two-hump-structured spectral energy distribution (SED) peaks at higher energies with respect to conventional blazars. Multiwavelength (MWL) observations constrain their synchrotron peak in the medium to hard X-ray band. Their gamma-ray SED peaks above the GeV band, and in some objects it extends up to several TeV. Up to now, only a few EHBLs have been detected in the TeV gamma-ray range. In this paper, we report the detection of the EHBL 2WHSP J073326.7+515354, observed and detected during 2018 in TeV gamma rays with the MAGIC telescopes. The broad-band SED is studied within an MWL context, including an analysis of the Fermi-LAT data over 10 yr of observation and with simultaneous Swift-XRT, Swift-UVOT, and KVA data. Our analysis results in a set of spectral parameters that confirms the classification of the source as an EHBL. In order to investigate the physical nature of this extreme emission, different theoretical frameworks were tested to model the broad-band SED. The hard TeV spectrum of 2WHSP J073326.7+515354 sets the SED far from the energy equipartition regime in the standard one-zone leptonic scenario of blazar emission. Conversely, more complex models of the jet, represented by either a two-zone spine-layer model or a hadronic emission model, better represent the broad-band SED.

scholarly journals The challenging SED of AP Librae

2011 ◽  
Vol 7 (S284) ◽  
pp. 411-413 ◽  
Author(s):  
David Sanchez ◽  
Berrie Giebels ◽  
Pascal Fortin ◽  
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
Low Frequency ◽  
Theoretical Models ◽  
Intermediate Frequency ◽  
High Energy ◽  
Spectral Energy ◽  
Broad Band Emission ◽  
Band Emission ◽  
Bl Lac

AbstractMatching the broad-band emission of active galaxies with the predictions of theoretical models can be used to derive constraints on the properties of the emitting region and to probe the physical processes involved. AP Librae is the third low frequency peaked BL Lac (LBL) detected at very high energy (VHE, E>100GeV) by an Atmospheric Cherenkov Telescope; most VHE BL Lacs (34 out of 39) belong to the high-frequency and intermediate-frequency BL Lac classes (HBL and IBL). LBL objects tend to have a higher luminosity with lower peak frequencies than HBLs or IBLs. The characterization of their time-averaged spectral energy distribution is challenging for emission models such as synchrotron self-Compton (SSC) models.

scholarly journals Multimessenger observations of counterparts to IceCube-190331A

2020 ◽  
Vol 497 (3) ◽  
pp. 2553-2561
Author(s):  
Felicia Krauß ◽  
Emily Calamari ◽  
Azadeh Keivani ◽  
Alexis Coleiro ◽  
Phil A Evans ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
Ultra High Energy ◽  
X Ray ◽  
High Energy Cosmic Rays ◽  
High Energies ◽  
Neutrino Event ◽  
Promising Tool ◽  
Localization Region

ABSTRACT High-energy neutrinos are a promising tool for identifying astrophysical sources of high and ultra-high energy cosmic rays (UHECRs). Prospects of detecting neutrinos at high energies (≳TeV) from blazars have been boosted after the recent association of IceCube-170922A and TXS 0506+056. We investigate the high-energy neutrino, IceCube-190331A, a high-energy starting event (HESE) with a high likelihood of being astrophysical in origin. We initiated a Swift/XRT and UVOT tiling mosaic of the neutrino localization and followed up with ATCA radio observations, compiling a multiwavelength spectral energy distribution (SED) for the most likely source of origin. NuSTAR observations of the neutrino location and a nearby X-ray source were also performed. We find two promising counterpart in the 90 per cent confidence localization region and identify the brightest as the most likely counterpart. However, no Fermi/LAT γ-ray source and no prompt Swift/BAT source is consistent with the neutrino event. At this point, it is unclear whether any of the counterparts produced IceCube-190331A. We note that the Helix Nebula is also consistent with the position of the neutrino event and we calculate that associated particle acceleration processes cannot produce the required energies to generate a high-energy HESE neutrino.

scholarly journals Monitoring of the radio galaxy M 87 at Very High Energy with MAGIC during a low emission state between 2012 and 2015

2016 ◽  
Vol 12 (S324) ◽  
pp. 164-167
Author(s):  
C. Arcaro ◽  
P. Bangale ◽  
M. Manganaro ◽  
D. Mazin ◽  
P. Colin ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Spectral Energy Distribution ◽  
Photon Emission ◽  
High Energy ◽  
Spectral Energy ◽  
X Rays ◽  
Low Emission ◽  
Very High Energy ◽  
Alternative Scenarios ◽  
Very High

AbstractWe present the preliminary results from observing the nearby radio galaxy M 87 for 156 hours (between the years 2012 and 2015) with the MAGIC telescopes, which lead to a significant very high energy (VHE, E > 100 GeV) detection of the source in quiescent states each year. Our VHE analysis combined with quasi-simultaneous data at other energies (from gamma-rays, X-rays, optical and radio) provides a unique opportunity to study the source variability and its broadband spectral energy distribution, which is found to disfavour a one-zone synchrotron/synchrotron self-Compton model. Therefore, other alternative scenarios for the photon emission are explored. We also find that the VHE emission is compatible with being produced close to the source radio core as previous data already indicated. A detailed paper presenting full results of the observing campaign is in preparation.

scholarly journals Constraining X-ray emission in HBL blazars using multiwavelength observations

2020 ◽  
Vol 496 (2) ◽  
pp. 1295-1306
Author(s):  
Alicja Wierzcholska ◽  
Stefan J Wagner
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
Neutral Hydrogen ◽  
High Energy ◽  
Host Galaxy ◽  
Spectral Energy ◽  
Additional Absorption ◽  
X Ray ◽  
Uv Excess ◽  
Survey Results

ABSTRACT The X-ray spectrum of extreme high-energy peaked BL Lac-type blazars is located in the synchrotron branch of the broad-band spectral energy distribution (SED), at energies below the peak. A joint fit of the extrapolated X-ray spectra together with a host galaxy template allows characterizing the synchrotron branch in the SED. The X-ray spectrum is usually characterized either with a pure or a curved power-law model. In the latter case, however, it is hard to distinguish an intrinsic curvature from excess absorption. In this paper, we focus on five well-observed blazars: 1ES 0229+200, PKS 0548−322, RX J 1136+6737, 1ES 1741+196, and 1ES 2344+514. We constrain the infrared to X-ray emission of these five blazars using a model that is characterized by the host galaxy, spectral curvature, absorption, and ultraviolet (UV) excess to separate these spectral features. In the case of four sources, namely 1ES 0229+200, PKS 0548−322, 1ES 1741+196, and 1ES 2344+514, the spectral fit with the atomic neutral hydrogen from the Leiden Argentina Bonn Survey results in a significant UV excess present in the broad-band SED. Such excess can be interpreted as an additional component, for example, a blue bump. However, in order to describe spectra of these blazars without such excess, additional absorption to the atomic neutral hydrogen from the Leiden Argentina Bonn Survey is needed.

Energy-dependent nebula extent and spatially resolved spectra of the pulsar wind nebula 3C 58

2020 ◽  
Vol 498 (2) ◽  
pp. 1911-1919
Author(s):  
Fang-Wu Lu ◽  
Quan-Gui Gao ◽  
Li Zhang
Keyword(s):  
Surface Brightness ◽  
Spectral Energy Distribution ◽  
High Energy ◽  
Spatial Variations ◽  
Spectral Energy ◽  
X Ray ◽  
Spatially Resolved ◽  
Photon Index ◽  
Pulsar Wind ◽  
Energy Dependent

ABSTRACT 3C 58 is a pulsar wind nebula (PWN) that shows an interesting energy-dependent nebula extent and spatial variations of the photon index and surface brightness in the X-ray band. These observations provide useful information with which to study the spatially dependent radiative cooling of electrons and the energy-dependent transport mechanisms within the nebula. In this paper, the energy-dependent nebula extent and spatially resolved spectra of this PWN are investigated in the framework of a spatially dependent particle transport model. The observations of the nebula, including the photon spectral energy distribution, spatial variations of the X-ray spectrum, and measurements of the nebula extent, can be naturally explained in this model. Our results show that the energy-dependent nebula extent favours an advection–diffusion scenario with advection-dominated transport, and the variations of the nebula extent with energy in the X-ray band can be attributed to the cooling losses of high-energy electrons affected by synchrotron burn-off. Particle diffusion plays an important role in modifying the spatial variations of the photon index and surface brightness in the X-ray band. The radial extents of the nebula at radio, GeV and TeV energies are predicted by the model, indicating that the nebula extent of 3C 58 varies with energy in these bands. The analyses show that the dependence of the adiabatic cooling rate and synchrotron radiation on the spectral index of injected particles is important for changing the nebula extent at different energies.

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