Modeling the broadband spectra and variability of blazars

Böttcher, M.

doi:10.1016/j.newar.2003.12.017

Cited by 4 publications

(4 citation statements)

References 48 publications

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“…However, during violent flares significant variation has been seen in the TeV photon index for some AGN [174]; this supports the case for SSC models, where cooling of synchrotron electrons is believed to lead to spectral hardening with increasing flux at x-ray (and therefore at gamma-ray) energies [175], as shown in figure 16. Studies of these phenomena at TeV energies have been difficult due to the long exposures required to have enough photons to measure a meaningful spectrum.…”

Section: Active Galactic Nuclei (Agn)supporting

confidence: 73%

TeV gamma-ray astronomy

Chadwick

Latham²,

Nolan³

2008

J. Phys. G: Nucl. Part. Phys.

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Covering a broad energy range from ∼100 GeV to 100 TeV and above, celestial TeV gamma rays are accessed by telescopes based on the ground, unlike x-rays and lower energy gamma rays, which can only be detected using instruments in space. The natural advantage this gives such telescopes in terms of collection area is now being exploited by a generation of instruments with unprecedented sensitivity and angular resolution, and these are revealing a Universe rich in new phenomena. This paper briefly describes the techniques and telescopes currently in operation, reviews some highlights so far, provides a catalogue of sources as of May 2007 and looks at some likely future observatories and experiments.

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Section: Active Galactic Nuclei (Agn)supporting

confidence: 73%

TeV gamma-ray astronomy

Chadwick

Latham²,

Nolan³

2008

J. Phys. G: Nucl. Part. Phys.

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“…Except for J0849+5108, for which the dataset does not cover a substantial number of activity cycles, the remaining three sources show intense variability at practically all frequencies, a behaviour commonly seen in blazars (e.g. Richards et al, 2011;Aller et al, 2011;Boettcher, 2012;Böttcher, 2004). The phenomenologies seen in these light curves vary significantly and mostly in terms of the observed amplitude of the different events.…”

Section: Radio Light Curvesmentioning

confidence: 99%

Radio jet emission from GeV-emitting narrow-line Seyfert 1 galaxies

Angelakis

Fuhrmann

Marchili

et al. 2015

A&A

113

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Context. With the current study we aim at understanding the properties of radio emission and the assumed jet from four radio-loud and γ-ray-loud narrow-line Seyfert 1 galaxies that have been detected by Fermi. These are Seyfert 1 galaxies with emission lines at the low end of the FWHM distribution. Aims. The ultimate goal is twofold: first we investigate whether a relativistic jet is operating at the source producing the radio output, and second, we quantify the jet characteristics to understand possible similarities with and differences from the jets found in typical blazars. Methods. We relied on the most systematic monitoring of radio-loud and γ-ray-detected narrow-line Seyfert 1 galaxies in the cm and mm radio bands conducted with the Effelsberg 100 m and IRAM 30 m telescopes. It covers the longest time-baselines and the most radio frequencies to date. This dataset of multi-wavelength, long-term radio light-curves was analysed from several perspectives. We developed a novel algorithm to extract sensible variability parameters (mainly amplitudes and time scales) that were then used to compute variability brightness temperatures and the corresponding Doppler factors. The jet powers were computed from the light curves to estimate the energy output and compare it with that of typical blazars. The dynamics of radio spectral energy distributions were examined to understand the mechanism causing the variability. Results. The length of the available light curves for three of the four sources in the sample allowed a firm understanding of the general behaviour of the sources. They all display intensive variability that appears to be occurring at a pace rather faster than what is commonly seen in blazars. The flaring events become progressively more prominent as the frequency increases and show intensive spectral evolution that is indicative of shock evolution. The variability brightness temperatures and the associated Doppler factors are moderate, implying a mildly relativistic jet. The computed jet powers show very energetic flows. The radio polarisation in one case clearly implies a quiescent jet underlying recursive flaring activity. Finally, in one case, the sudden disappearance of a γ-ray flare below some critical frequency in our band needs a more detailed investigation of the possible mechanism causing the evolution of broadband events. Conclusions. Despite the generally lower flux densities, the sources appear to show all typical characteristics seen in blazars that are powered by relativistic jets, such as intensive variability, spectral evolution across the different bands following evolutionary paths explained by travelling shocks, and Doppler factors indicating mildly relativistic speeds.

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“…The Watcher Robotic Telescope is equipped with a Andor EMCCD, also for photometric observations. The Watcher Robotic Telescope is part of the GLORIA project 2 and focuses on follow-up optical photometry of gamma-ray bursts, though free time can and has been used for monitoring of AGN sources (see e.g. [9]).…”

Section: Boyden Observatorymentioning

confidence: 99%

“…In addition, blazars can be subdivided into Low, Intermediate, and High Synchrotron peaked, based on the observed peak in the Synchrotron component. See, for example, [2] and references therein for a more detailed discussion.…”

Section: Introductionmentioning

confidence: 99%

Search for Very High Energy Candidate Sources Among the Fermi Sources

Soelen¹,

Klindt²,

Meintjes³

et al. 2016

Proceedings of Frontier Research in Astrophysics — PoS(FRAPWS2014)

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The Fermi gamma-ray telescope has detected a host of new gamma-ray sources since it began operation. While the 2LAC catalogue classifies 1017 extragalactic sources, there is still no clear association with approximately 18 per cent of them. We are undertaking a multi-wavelength campaign to identify the counter parts of these sources and search for potential Very High Energy (VHE) candidates. The project is focussing on southern hemisphere sources and undertaking observations from South African observatories. The early stages of this project have focussed on identifying candidate sources and undertaking optical spectroscopy observations with the Southern African Large Telescope (SALT) and the SAAO 1.9-m telescope located at the Southern African Astronomical Observatory (SAAO). We present an overview of this multi-wavelength project along with recent results obtained.

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Modeling the broadband spectra and variability of blazars

Cited by 4 publications

References 48 publications

TeV gamma-ray astronomy

TeV gamma-ray astronomy

Radio jet emission from GeV-emitting narrow-line Seyfert 1 galaxies

Search for Very High Energy Candidate Sources Among the Fermi Sources

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