Fermi: Monitoring the Gamma-Ray Universe

Thompson, D. J.

doi:10.3390/galaxies6040117

Cited by 12 publications

(14 citation statements)

References 34 publications

(35 reference statements)

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“…We use gamma-ray data from the Fermi Gamma-ray Space Telescope. The Large Area Telescope (LAT) of the satellite is scanning the whole sky, and therefore it is a perfect instrument for systematic long-term studies [21]. Public light curves are available in weekly and daily binning 4,5 .…”

Section: Data Samplementioning

confidence: 99%

Fractional Variability—A Tool to Study Blazar Variability

et al. 2019

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Active Galactic Nuclei emit radiation over the whole electromagnetic spectrum up to TeV energies. Blazars are one subtype with their jets pointing towards the observer. One of their typical features is extreme variability on timescales, from minutes to years. The fractional variability is an often used parameter for investigating the degree of variability of a light curve. Different detection methods and sensitivities of the instruments result in differently binned data and light curves with gaps. As they can influence the physics interpretation of the broadband variability, the effects of these differences on the fractional variability need to be studied. In this paper, we study the systematic effects of completeness in time coverage and the sampling rate. Using public data from instruments monitoring blazars in various energy ranges, we study the variability of the bright TeV blazars Mrk 421 and Mrk 501 over the electromagnetic spectrum, taking into account the systematic effects, and compare our findings with previous results. Especially in the TeV range, the fractional variability is higher than in previous studies, which can be explained by the much longer (seven years compared to few weeks) and more complete data sample.

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Section: Data Samplementioning

confidence: 99%

Fractional Variability—A Tool to Study Blazar Variability

et al. 2019

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“…The resulting light curve is shown in Figure 5. 1 Data obtained using optical observations from the northern hemisphere, indicate that the optical light curve followed a similar, symmetric trend as the γ-ray flux past January 2017 [20]. The 2016-2017 outburst has been modeled using the model described briefly above.…”

Section: Resultsmentioning

confidence: 99%

The Long-Lasting Activity in the Flat Spectrum Radio Quasar (FSRQ) CTA 102

et al. 2019

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The flat spectrum radio quasar CTA 102 (z = 1.032) went through a tremendous phase of variability. Since early 2016 the gamma-ray flux level has been significantly higher than in previous years. It was topped by a four month long giant outburst, where peak fluxes were more than 100 times higher than the quiescence level. Similar trends are observable in optical and X-ray energies. We have explained the giant outburst as the ablation of a gas cloud by the relativistic jet that injects additional matter into the jet and can self-consistently explain the long-term light curve. Here, we argue that the cloud responsible for the giant outburst is part of a larger system that collides with the jet and is responsible for the years-long activity in CTA 102.

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“…This rules out additive processes for the origin of the observed variability and instead favors multiplicative ones. 4 If this is true, then additive models (e.g., shot-noise or a simple superposition of many "mini-jets") are no longer adequate to describe the observed variability behavior, and multiplicative, cascade-like scenarios need to be invoked. 4 For a stationary stochastic process X that results from a multiplication of N random subprocesses x i , X = ∏ x i , the logarithm of X is equivalent to the sum of the logarithm of the individual x i , i.e., log X = log x 1 + log x 2 + ... + log x N .…”

Section: Pdf Shape and Log-normalitymentioning

confidence: 99%

Gamma-Ray Astrophysics in the Time Domain

Rieger

2019

Galaxies

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The last few years have seen gamma-ray astronomy maturing and advancing in the field of time-domain astronomy, utilizing source variability on timescales over many orders of magnitudes, from a decade down to a few minutes and shorter, depending on the source. This review focuses on some of the key science issues and conceptual developments concerning the timing characteristics of active galactic nuclei (AGN) at gamma-ray energies. It highlights the relevance of adequate statistical tools and illustrates that the developments in the gamma-ray domain bear the potential to fundamentally deepen our understanding of the nature of the emitting source and the link between accretion dynamics, black hole physics, and jet ejection.

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Fermi: Monitoring the Gamma-Ray Universe

Cited by 12 publications

References 34 publications

Fractional Variability—A Tool to Study Blazar Variability

Fractional Variability—A Tool to Study Blazar Variability

The Long-Lasting Activity in the Flat Spectrum Radio Quasar (FSRQ) CTA 102

Gamma-Ray Astrophysics in the Time Domain

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