scholarly journals Prospects for γ-ray observations of narrow-line Seyfert 1 galaxies with the Cherenkov Telescope Array – II. γ–γ absorption in the broad-line region radiation fields

2020 ◽  
Vol 494 (1) ◽  
pp. 411-424 ◽  
Author(s):  
P Romano ◽  
M Böttcher ◽  
L Foschini ◽  
C Boisson ◽  
S Vercellone ◽  
...  
Keyword(s):  
High Energy ◽  
Emission Region ◽  
Broad Line ◽  
Narrow Line ◽  
Telescope Array ◽  
Cherenkov Telescope ◽  
Broad Line Region ◽  
Radiation Fields ◽  
Line Region ◽  
Γ Ray

ABSTRACT Gamma-ray emitting narrow-line Seyfert 1 (γ-NLS1) galaxies possibly harbour relatively low-mass black holes (106–108 M⊙) accreting close to the Eddington limit, and share many characteristics with their sibling sources, flat-spectrum radio quasars. Although they have been detected in the MeV–GeV band with Fermi–LAT, they have never been seen in the very high energy band with current imaging atmospheric Cherenkov telescopes (IACTs). Thus, they are key targets for the next-generation IACT, the Cherenkov Telescope Array (CTA). In a previous work we selected, by means of extensive simulations, the best candidates for a prospective CTA detection (SBS 0846+513, PMN J0948+0022, and PKS 1502+036) taking into account the effects of both the intrinsic absorption (approximated with a cut-off at 30 GeV), and the extragalactic background light on the propagation of γ-rays. In this work, we simulate the spectra of these three sources by adopting more realistic broad-line region (BLR) absorption models. In particular, we consider the detailed treatment of γ–γ absorption in the radiation fields of the BLR as a function of the location of the γ-ray emission region with parameters inferred from observational constraints. We find that, due to the energy range extent and its sensitivity, CTA is particularly well suited to locate the γ-ray emitting region in γ-NLS1. In particular CTA will be able not only to distinguish whether the γ-ray emitting region is located inside or outside the BLR, but also where inside the BLR it may be.

scholarly journals Physical inference from the γ-ray, X-ray, and optical time variability of a large sample of Fermi blazars

2019 ◽  
Vol 490 (1) ◽  
pp. 124-134
Author(s):  
Anwesh Majumder ◽  
Kaustav Mitra ◽  
Ritaban Chatterjee ◽  
C M Urry ◽  
C D Bailyn ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cross Correlation ◽  
Time Lag ◽  
Monitoring Program ◽  
Emission Region ◽  
Broad Line ◽  
X Ray ◽  
Broad Line Region ◽  
Line Region ◽  
Γ Ray

ABSTRACT We present cross-correlation studies of γ-ray (0.1–300 GeV), X-ray (0.2–10 keV), and optical (R band) variability of a sample of 26 blazars during 2008–2016. The light curves are from Fermi-LAT, Swift-XRT, and the Yale-SMARTS blazar monitoring program. We stack the discrete cross-correlation functions of the blazars such that the features that are consistently present in a large fraction of the sample become more prominent in the final result. We repeat the same analysis for two subgroups, namely, low synchrotron peaked (LSP) and high synchrotron peaked (HSP) blazars. We find that, on average, the variability at multiple bands is correlated, with a time lag consistent with zero in both subgroups. We describe this correlation with a leptonic model of non-thermal emission from blazar jets. By comparing the model results with those from the actual data, we find that the inter-band cross-correlations are consistent with an emission region of size 0.1 pc within the broad-line region for LSP blazars. We rule out large changes of magnetic field (>0.5 Gauss) across the emission region or small values of magnetic field (e.g., 0.2 Gauss) for this population. We also find that the observed variability of the HSP blazars can be explained if the emission region is much larger than the distance to the broad-line region from the central black hole.

scholarly journals Excluding possible sites of high-energy emission in 3C 84

2020 ◽  
Vol 500 (4) ◽  
pp. 4671-4677
Author(s):  
Lena Linhoff ◽  
Alexander Sandrock ◽  
Matthias Kadler ◽  
Dominik Elsässer ◽  
Wolfgang Rhode
Keyword(s):  
Black Hole ◽  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
Emission Region ◽  
Broad Line ◽  
Central Black Hole ◽  
Broad Line Region ◽  
Ring Geometry ◽  
Line Region

ABSTRACT The FR-I galaxy 3C 84, that is identified with the misaligned blazar NGC 1275, is well known as one of the very few radio galaxies emitting gamma-rays in the TeV range. Yet, the gamma-ray emission region cannot be pinpointed and the responsible mechanisms are still unclear. We calculate the optical absorption depth of high-energy photons in the broad-line region of 3C 84 depending on their energy and distance to the central black hole. Based on these calculations, a lower limit on the distance of the emission region from the central black hole can be derived. These lower limits are estimated for two broad-line region geometries (shell and ring) and two states of the source, the low state in 2016 October–December and a flare state in 2017 January. For the shell geometry, we can place the emission region outside the Ly α radius. For the ring geometry and the low flux activity, the minimal distance between the black hole, and the gamma-ray emission region is close to the Ly α radius. In the case of the flaring state (ring geometry), the results are not conclusive. Our results exclude the region near the central black hole as the origin of the gamma-rays detected by Fermi–LAT and Major Atmospheric Gamma-Ray Imaging Cherenkov. With these findings, we can constrain the theoretical models of acceleration mechanisms and compare the possible emission region to the source’s morphology resolved by radio images from the Very Long Baseline Array.

scholarly journals Probing the absorption of gamma-rays by IR radiation from the dusty torus in FSRQs with the Cherenkov telescope array

2020 ◽  
Vol 495 (3) ◽  
pp. 3463-3473 ◽  
Author(s):  
Giorgio Galanti ◽  
Marco Landoni ◽  
Fabrizio Tavecchio ◽  
Stefano Covino
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Emission Region ◽  
Emission Model ◽  
Ir Radiation ◽  
Telescope Array ◽  
Cherenkov Telescope ◽  
Line Region ◽  
Uv Photons ◽  
Dusty Torus

ABSTRACT Within the classical emission model, where the emission region is placed within the broad line region (BLR), flat spectrum radio quasars (FSRQs) were believed not to emit photons with energies above few tens of GeV because of the absorption with the optical-UV photons from the BLR. However, photons with observed energies up to about $300 \, \rm GeV$ have been detected for few FSRQs, whose most iconic example is PKS 1441+25 at redshift z = 0.94. The most conservative explanation for these observations is that the emission occurs at distances comparable to the size of the dusty torus. In this case, absorption of high-energy gamma-ray photons for energies above $200{-}300 \, {\rm GeV}$ is dominated by the interaction with infrared radiation emitted by the torus. We investigate if current observational data about FSRQs in flaring state can give us information about: (i) the importance of the torus absorption and (ii) the properties of the torus i.e. its temperature and its geometry. We find that present data do not arrive at energies where the torus influence is prominent and as a result it is currently hardly possible to infer torus properties from observations. However, with dedicated simulations, we demonstrate that observations with the forthcoming Cherenkov Telescope Array (CTA) will be able to constrain the torus parameters (temperature and geometry).

scholarly journals Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with H.E.S.S.

2019 ◽  
Vol 627 ◽  
pp. A159 ◽  
Author(s):  
◽  
H. Abdalla ◽  
R. Adam ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
...  
Keyword(s):  
Black Hole ◽  
Lorentz Invariance ◽  
High Energy ◽  
Emission Region ◽  
Physical Parameters ◽  
Broad Line ◽  
Data Set ◽  
Broad Line Region ◽  
Link Type ◽  
Line Region

The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV <  E <  100 GeV) γ-ray band, which is continuously monitored with Fermi-LAT. During two periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E >  100 GeV) γ-ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8.7σ significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 ± 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r ≳ 1.7 × 1017 cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279.

scholarly journals Gamma rays from jets interacting with BLR clouds in blazars

2019 ◽  
Vol 623 ◽  
pp. A101 ◽  
Author(s):  
S. del Palacio ◽  
V. Bosch-Ramon ◽  
G. E. Romero
Keyword(s):  
Thermal Emission ◽  
Strong Shock ◽  
High Energy ◽  
Broad Line ◽  
High Energy Radiation ◽  
Broad Line Region ◽  
Photon Field ◽  
Cloud Dynamics ◽  
Line Region ◽  
Inverse Compton

Context. The innermost parts of powerful jets in active galactic nuclei are surrounded by dense, high-velocity clouds from the broad-line region, which may penetrate into the jet and lead to the formation of a strong shock. Such jet-cloud interactions are expected to have measurable effects on the γ-ray emission from blazars. Aims. We characterise the dynamics of a typical cloud-jet interaction scenario, and the evolution of its radiative output in the 0.1–30 GeV energy range, to assess to what extent these interactions can contribute to the γ-ray emission in blazars. Methods. We use semi-analytical descriptions of the jet-cloud dynamics, taking into account the expansion of the cloud inside the jet and its acceleration. Assuming that electrons are accelerated in the interaction and making use of the hydrodynamical information, we then compute the high-energy radiation from the cloud, including the absorption of γ-rays in the ambient photon field through pair creation. Results. Jet-cloud interactions can lead to significant γ-ray fluxes in blazars with a broad-line region (BLR), in particular when the cloud expansion and acceleration inside the jet are taken into account. This is caused by 1) the increased shocked area in the jet, which leads to an increase in the energy budget for the non-thermal emission; 2) a more efficient inverse Compton cooling with the boosted photon field of the BLR; and 3) an increased observer luminosity due to Doppler boosting effects. Conclusions. For typical broad-line region parameters, either (i) jet-cloud interactions contribute significantly to the persistent γ-ray emission from blazars or (ii) the BLR is far from spherical or the fraction of energy deposited in non-thermal electrons is small.

scholarly journals Near-IR Spectroscopy of High-z QSOs: Relating the Broad and Narrow-Line Regions

1997 ◽  
Vol 159 ◽  
pp. 258-259
Author(s):  
M.S. Brotherton
Keyword(s):  
Simple Model ◽  
Broad Line ◽  
Narrow Line ◽  
Strong Correlations ◽  
Broad Line Region ◽  
Near Ir ◽  
Line Region ◽  
Derived Properties ◽  
Narrow Line Region ◽  
Line Widths

Recent investigations of the broad UV lines in luminous QSOs identified strong correlations involving emission-line widths, shifts, equivalent widths, and ratios (Francis et al. 1992; Wills et al. 1993; Brotherton et al. 1994a, b). A simple model developed to explain these trends approximates UV broad lines as emission from two regions, an intermediate-line region (ILR), and a very broad-line region (VBLR), together comprising the traditional broad-line region (BLR). The observed and derived properties for the ILR and VBLR are summarized in Table 1, along with typical values for the narrow-line region (NLR).

scholarly journals Magnetization of AGN jets as imposed by leptonic models of luminous blazars

2014 ◽  
Vol 10 (S313) ◽  
pp. 85-86
Author(s):  
Mateusz Janiak ◽  
Marek Sikora ◽  
Rafal Moderski
Keyword(s):  
Black Hole ◽  
Kinetic Energy ◽  
Energy Flux ◽  
Broad Line ◽  
Jet Formation ◽  
Frequency Dependent ◽  
Broad Line Region ◽  
Line Region ◽  
Γ Ray ◽  
Dusty Torus

AbstractRecent measurements of frequency-dependent shift of radio-core locations indicate that the ratio of the magnetic to kinetic energy flux (the σ parameter) is of the order of unity. These results are consistent with predictions of magnetically-arrested-disk (MAD) models of a jet formation, but contradict the predictions of leptonic models of γ-ray production in luminous blazars. We demonstrate this discrepancy by computing the γ-ray-to-synchrotron luminosity ratio (the q parameter) as a function of a distance from the black hole for different values of σ and using both spherical and planar models for broad-line region and dusty torus. We find that it is impossible to reproduce observed q ≫ 1 for jets with σ ≥ 1. This may indicate that blazar radiation is produced in reconnection layers or in spines of magnetically stratified jets.

scholarly journals Unification of Radio Galaxies

1998 ◽  
Vol 164 ◽  
pp. 81-82
Author(s):  
M.H. Cohen ◽  
P.M. Ogle ◽  
H.D. Iran ◽  
R.W. Goodrich
Keyword(s):  
Radio Galaxies ◽  
Broad Line ◽  
Narrow Line ◽  
Spectral Classification ◽  
Broad Line Region ◽  
Line Region ◽  
Direct View

AbstractMany FR 2 narrow-line radio galaxies also display polarized broad lines. The broad-line region is hidden from direct view and is seen by reflection (ie scattering). In these objects the spectral classification is controlled by the aspect at which they are viewed.

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