HADRONIC MODELING OF AGN VARIABILITY

2012 ◽  
Vol 08 ◽  
pp. 293-298 ◽  
Author(s):  
FELIX SPANIER ◽  
MATTHIAS WEIDINGER
Keyword(s):  
Time Variation ◽  
Gamma Ray ◽  
Time Dependent ◽  
Emission Scenarios ◽  
Linear Processes ◽  
Bl Lac Objects ◽  
Variation Patterns ◽  
Bl Lac ◽  
Non Linear ◽  
Emission Models

The ongoing search for extragalactic gamma-ray sources reveals more and more blazars not classified as high-peaked BL Lac objects. These sources may not be understood in the context of purely leptonic emission models. In the present paper we study lepto-hadronic emission models, especially their time variation patterns. Since a number of non-linear processes are involved, timing relations are far more complex than in purely leptonic models and might eventually be used to discriminate different emission scenarios. First complete time dependent applications to 3C279 and 3C454.3 are presented.

VERITAS OBSERVATIONS OF RELATIVISTIC OUTFLOWS IN LOW- AND INTERMEDIATE-FREQUENCY-PEAKED BL LAC OBJECTS

2014 ◽  
Vol 28 ◽  
pp. 1460178
Author(s):  
◽  
HEIKE PROKOPH
Keyword(s):  
Gamma Ray ◽  
Intermediate Frequency ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs ◽  
Gamma Ray Telescopes ◽  
Very High

The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

scholarly journals Gamma-ray counterparts of 2WHSP high-synchrotron-peaked BL Lac objects as possible signatures of ultra-high-energy cosmic ray emission

2020 ◽  
Vol 497 (2) ◽  
pp. 2455-2468
Author(s):  
Michael W Toomey ◽  
Foteini Oikonomou ◽  
Kohta Murase
Keyword(s):  
Energy Range ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Potential Candidate ◽  
Ultra High Energy ◽  
Bl Lac Objects ◽  
Cherenkov Telescopes ◽  
Bl Lac ◽  
Γ Ray

ABSTRACT We present a search for high-energy γ-ray emission from 566 Active Galactic Nuclei at redshift z > 0.2, from the 2WHSP catalogue of high-synchrotron peaked BL Lac objects with 8 yr of Fermi-LAT data. We focus on a redshift range where electromagnetic cascade emission induced by ultra-high-energy cosmic rays can be distinguished from leptonic emission based on the spectral properties of the sources. Our analysis leads to the detection of 160 sources above ≈5σ (TS ≥25) in the 1–300 GeV energy range. By discriminating significant sources based on their γ-ray fluxes, variability properties, and photon index in the Fermi-LAT energy range, and modelling the expected hadronic signal in the TeV regime, we select a list of promising sources as potential candidate ultra-high-energy cosmic ray emitters for follow-up observations by Imaging Atmospheric Cherenkov Telescopes.

Optical spectroscopy of BL Lac objects: TeV candidates

2020 ◽  
Vol 497 (1) ◽  
pp. 94-108 ◽  
Author(s):  
Simona Paiano ◽  
Renato Falomo ◽  
Aldo Treves ◽  
Riccardo Scarpa
Keyword(s):  
Lower Limit ◽  
Gamma Ray ◽  
Absorption Lines ◽  
Host Galaxies ◽  
Stellar Objects ◽  
Bl Lac Objects ◽  
Forbidden Transition ◽  
Bl Lac ◽  
Quasi Stellar Objects ◽  
Relationship Of

ABSTRACT We investigate the spectroscopic optical properties of gamma-ray sources detected with high significance above 50 GeV in the Third Catalog of Hard Fermi-LAT Sources and that are good candidates as TeV emitters. We focus on the 91 sources that are labelled by the Fermi team as BL Lac (BLL) objects or blazar candidates of uncertain type (BCUs), are in the Northern hemisphere, and are with unknown or uncertain redshift. We report here on GTC (Gran Telescopio Canarias) spectra (in the spectral range 4100–7750 Å) of 13 BCUs and 42 BLL objects. We are able to classify the observed targets as BLL objects and each source is briefly discussed. The spectra allowed us to determine the redshift of 25 objects on the basis of emission and/or absorption lines, finding 0.05 < z < 0.91. Most of the emission lines detected are due to forbidden transition of [O iii] and [N ii]. The observed line luminosity is found to be lower than that of quasi-stellar objects (QSOs) at similar continuum and could be reconciled with the line–continuum luminosity relationship of QSOs if a significant beaming factor is assumed. Moreover, for five sources we found intervening absorption lines that allow to set a spectroscopic lower limit of the redshift. For the remaining 25 sources, for which the spectra are lineless, a lower limit to z is given, assuming that the host galaxies are giant ellipticals.

Radio-faint BL Lac objects and their impact on the radio/gamma-ray connection

2012 ◽  
Vol 49 (9) ◽  
pp. 1320-1326 ◽  
Author(s):  
Marcello Giroletti ◽  
V. Pavlidou ◽  
A. Reimer ◽  
G.B. Taylor ◽  
G. Tosti ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Bl Lac Objects ◽  
Bl Lac

scholarly journals The γ-ray sky seen at X-ray energies

2020 ◽  
Vol 638 ◽  
pp. A128 ◽  
Author(s):  
E. J. Marchesini ◽  
A. Paggi ◽  
F. Massaro ◽  
N. Masetti ◽  
R. D’Abrusco ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Large Fraction ◽  
Large Area ◽  
Bl Lac Objects ◽  
X Ray ◽  
Positional Uncertainty ◽  
Bl Lac ◽  
Frequency Behavior ◽  
Bl Lacs ◽  
Selection Of

Context. Nearly 50% of all sources detected by the Fermi Large Area Telescope are classified as blazars or blazar candidates, one of the most elusive classes of active galaxies. Additional blazars can also be hidden within the sample of unidentified or unassociated γ-ray sources (UGSs) that constitute about one-third of all gamma-ray sources detected to date. We recently confirmed that the large majority of Fermi blazars of the BL Lac subclass have an X-ray counterpart. Aims. Using the X-ray properties of a BL Lac training set and combining these with archival multifrequency information, we aim to search for UGSs that could have a BL Lac source within their γ-ray positional uncertainty regions. Methods. We reduced and analyzed the Swift X-ray observations of a selected sample of 327 UGSs. We then compared the X-ray fluxes and hardness ratios of all sources detected in the pointed fields with those of known Fermi BL Lacs. Results. We find at least one X-ray source, lying within the γ-ray positional uncertainty at 95% confidence level, for 223 UGSs and a total of 464 X-ray sources in all fields analyzed. The X-ray properties of a large fraction of them, eventually combined with radio, infrared, and optical information, exhibit BL Lac multi-frequency behavior, thus allowing us to select high-confidence BL Lac candidates; some of them were recently observed during our optical spectroscopic campaign which confirmed their nature. Conclusions. We find that out of 50 X-ray sources that were confirmed as BL Lacs through optical spectroscopy, 12 do not show canonical mid-infrared or radio BL Lac properties. This indicates that the selection of X-ray BL Lac candidates is a strong method to find new counterparts within Fermi UGSs. Finally, we pinpoint a sample of 32 Swift/XRT candidate counterparts to Fermi UGSs that are most likely BL Lac objects.

scholarly journals High Energy Phenomena in AGN Jets

1998 ◽  
Vol 188 ◽  
pp. 153-156
Author(s):  
F. Takahara
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Line Of Sight ◽  
Time Variability ◽  
Optical Polarization ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Bl Lac ◽  
Gamma Ray Emission ◽  
Superluminal Expansion

BL-Lac objects and optically violent variable quasars (OVVs), called together blazars, are characterized by rapid time variability, strong optical polarization, superluminal expansion and strong gamma-ray emission. Such properties are understood in the framework of a relativistic jet emanated from the central powerhouse. Blazars are considered to be objects for which the direction of the jet is very close to the line of sight.

Gamma-ray Emission from the γ-ray-loud BL Lac Objects

2001 ◽  
Vol 1 (6) ◽  
pp. 494-500 ◽  
Author(s):  
Guang-Zhong Xie ◽  
Ben-Zhong Dai ◽  
En-Wei Liang ◽  
Zhao-Hua Xie
Keyword(s):  
Gamma Ray ◽  
Bl Lac Objects ◽  
Bl Lac ◽  
Γ Ray ◽  
Gamma Ray Emission
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