Beamed and Unbeamed Emission of γ-Ray Blazars Pei, Zhiyuan; Fan, Junhui; Yang, Jianghe ...
Publications of the Astronomical Society of the Pacific,
11/2020, Letnik:
132, Številka:
1017
Journal Article
Recenzirano
Odprti dostop
A two-component model of radio emission has been used to explain some radio observational properties of Active Galactic Nuclei (AGNs) and, in particular, of blazars. In this work, we extend the ...two-component idea to the γ-ray emission and assume that the total γ-ray output of blazars consists of relativistically beamed and unbeamed components. The basic idea leverages the correlation between the radio core-dominance parameter and the γ-ray beaming factor. To do so, we evaluate this correlation for a large sample of 584 blazars taken from the fourth source catalog of the Fermi Large Area Telescope (Fermi-LAT) and correlated their γ-ray core-dominance parameters with radio core-dominance parameters. The γ-ray beaming factor is then used to estimate the beamed and unbeamed components. Our analysis confirms that the γ-ray emission in blazars is mainly from the beamed component.
We propose a nanosatellite Compton telescope based on a silicon tracker, both as a fast and low-cost mission for astrophysics in the MeV regime and as a pathfinder for future large-scale Compton ...orbital observatories. In this paper we assess the sensitivity of such an instrument for the observation of gamma-ray bursts.
Over the past two decades, both X-ray and gamma-ray astronomy have experienced great progress. However, the region of the electromagnetic spectrum around ∼1 MeV is not so thoroughly explored. Future ...medium-sized gamma-ray telescopes will fill this gap in observations. As the timescale for the development and launch of a medium-class mission is ∼10 years, with substantial costs, we propose a different approach for the immediate future. In this paper, we evaluate the viability of a much smaller and cheaper detector: a nano-satellite Compton telescope, based on the CubeSat architecture. The scientific performance of this telescope would be well below that of the instrument expected for the future larger missions; however, via simulations, we estimate that such a compact telescope will achieve a performance similar to that of COMPTEL.
S5 0716+714 is a well known BL Lac object, and one of the brightest and most active blazars. The discovery in the Very High Energy band (VHE, E > 100 GeV) by MAGIC happened in 2008. In January 2015, ...the source went through the brightest optical state ever observed, triggering MAGIC follow-up and a VHE detection with similar to 13 sigma significance (ATel sharp 6999 ). Rich multiwavelength coverage of the flare allowed us to construct the broad-band spectral energy distribution of S5 0716+714 during its brightest outburst. In this work, we will present the preliminary analysis of MAGIC and Fermi-LAT data of the flaring activity in January and February 2015 for the HE (0.1 < HE < 300 GeV) and VHE band, together with radio (Metsaehovi, OVRO, VLBA, Effelsberg), sub-millimeter (SMA), optical (Tuorla, Perkins, Steward, AZT-8+ST7, LX-200, Kanata), X-ray and UV (Swift-XRT and UVOT), in the same time-window and discuss the time variability of the multiwavelength light curves during this impressive outburst.
Highlights of MAGIC results Bastieri, Denis
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2008, Letnik:
588, Številka:
1-2
Journal Article
Recenzirano
MAGIC is the largest Cherenkov telescope currently operating and is in full operation since September 2004. Since then, it is providing a full wealth of exciting new physics results from its ...observations in the very high energy (VHE) region of galactic and extragalactic locations. Among the main results obtained, the discoveries of new sources and even of entire new classes of sources, as well as the observation of fast variability down to an unprecedented level of precision. Recent results for distant extragalactic sources are also shown: observations that are important for the development of new models of extragalactic background and to evaluate the systematic uncertainties of the imaging Cherenkov technique.
Identifying as yet undetected high-energy sources in the
γ
-ray sky is one of the declared objectives of the Fermi Large Area Telescope (LAT) Collaboration. We develop a Bayesian mixture model which ...is capable of disentangling the high-energy extra-galactic sources present in a given sky region from the pervasive background radiation. We achieve this by combining two model components. The first component models the emission activity of the single sources and incorporates the instrument response function of the Fermi
γ
-ray space telescope. The second component reliably reflects the current knowledge of the physical phenomena which underlie the
γ
-ray background. The model parameters are estimated using a reversible jump MCMC algorithm, which simultaneously returns the number of detected sources, their locations and relative intensities, and the background component. Our proposal is illustrated using a sample of the Fermi LAT data. In the analysed sky region, our model correctly identifies 116 sources out of the 132 present. The detection rate and the estimated directions and intensities of the identified sources are largely unaffected by the number of detected sources.
We present a sample of 4388 AGNs with available radio core-dominance parameters—defined as the ratio of the core flux densities to the extended ones,
R = S
core
/
S
ext
.—which includes 630
Fermi
...-detected AGNs from the fourth source catalog (4FGL) of the
Fermi
Large Area Telescope (
Fermi
/LAT); the rest are non-
Fermi
-detected AGNs. In our sample, 584 blazars are
Fermi
-detected and 1310 are not. The sample also contains other subclasses, such as Seyferts, Fanaroff-Riley I/II galaxies, and normal galaxies. We investigate various properties of the
Fermi
-detected and non-
Fermi
-detected AGNs by using core-dominance parameters, capitalizing on a previous study which showed that
R
is a good indicator of beaming. We then calculate radio spectral indices for the whole sample, and adopt
γ
-ray-photon indices for the
Fermi
AGNs from the 4FGL catalog to discuss the properties of different subclasses. We obtain a relation between the core-dominance parameters and the radio spectral indices for both
Fermi
and non-
Fermi
sources, assuming a two-component model in the radio band. Our previous study ruled out the assumption that the core-dominance parameters and radio spectral indices are quite different for different AGN subclasses. This holds not only for
Fermi
sources but also for non-
Fermi
sources. In particular,
R
is, on average, greater for the former AGNs than for the latter. In this study, we enlarge our sample with available values of
R
to 4388 AGNs, and the obtained conclusions are consistent with our previous study. We assume that the same two-component model holds for the
γ
-ray band as for the radio band, and therefore, adopt the same relation between the core-dominance parameters and the
γ
-ray-photon indices for
Fermi
AGNs. Our fitting results indicate that the
γ
-ray emissions of
Fermi
blazars originate mainly from the jet, and therefore, we conclude that the
Fermi
blazars are beamed.
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