Systematic Search for γ-Ray Periodicity in Active Galactic Nuclei Detected by the Fermi Large Area Telescope

Peñil, Pablo; Domínguez, A.; Buson, S.; Ajello, M.; Otero-Santos, Jorge; Barrio, J. A.; Nemmen, Rodrigo; Cutini, S.; Rani, Bindu; Franckowiak, A.; Cavazzuti, E.

doi:10.3847/1538-4357/ab910d

Cited by 72 publications

(74 citation statements)

References 54 publications

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“…In this paper, to ensure a trade-off between the study of a sufficiently large set of LCs and computational limitations for the analysis a large amount of Fermi-LAT data, we chose to deploy the methods discussed in the following sections on monthly binned LCs. This LC sample has also been used to study the long-term variability and possible periodic behavior of the Fermi-LAT sources, see Peñil et al (2020).…”

Section: The Sample Of Fermi-lat Lightcurvesmentioning

confidence: 99%

Ornstein-Uhlenbeck parameter extraction from light curves of Fermi-LAT observed blazars

Burd

Kohlhepp

Wagner

et al. 2021

A&A

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Context. Monthly binned γ-ray light curves of 236 bright γ-ray sources, particularly blazars, selected from a sample of 2278 highgalactic latitude objects observed with Fermi-LAT show flux variability characterized by power spectral densities consisting of a single power-law component, ranging from Brownian to white noise. Aims. The main goal here is to assess the Ornstein-Uhlenbeck (OU) model by studying the range of its three parameters that reproduces these statistical properties. Methods. We develop procedures for extracting values of the three OU model parameters (mean flux, correlation length, and random amplitude) from time series data and apply them to compare numerical integrations of the OU process with the Fermi-LAT data. Results. The OU process fully describes the statistical properties of the flux variations of the 236 blazars. The distributions of the extracted OU parameters are narrowly peaked around well-defined values (σ, µ, θ) = (0.2, −8.4, 0.5) with variances (0.004, 0.07, 0.13). The distributions of rise and the decay time scales of flares in the numerical simulations, meaning major flux variations fulfilling predefined criteria, are in agreement with the observed ones. The power spectral densities of the synthetic light curves are statistically indistinguishable from those of the measured light curves. Conclusions. The long-term γ-ray flux variability of blazars on monthly time scales is well described by a stochastic model that involves only three parameters. The methods described here are powerful tools for studying randomness in light curves and thereby for constraining the physical mechanisms responsible for the observed flux variations.

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Section: The Sample Of Fermi-lat Lightcurvesmentioning

confidence: 99%

Ornstein-Uhlenbeck parameter extraction from light curves of Fermi-LAT observed blazars

Burd

Kohlhepp

Wagner

et al. 2021

A&A

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“…Search for periodicities in blazar (and AGN) light curves at all wavelengths have led to a variety of results (e.g. Lainela et al 1999;Raiteri et al 2001;Gierliński et al 2008;Ackermann et al 2015;Graham et al 2015;Gupta et al 2018;Otero-Santos et al 2020;Peñil et al 2020), and to discussions on their reliability (Vaughan et al 2016;Covino et al 2019). Up to now, the ∼ 12 yr (quasi) periodicity found in the BL Lac object OJ 287 is considered the most robust result and is interpreted in the framework of a binary black hole system (e.g.…”

mentioning

confidence: 99%

The dual nature of blazar fast variability: Space and ground observations of S5 0716+714

Raiteri

Villata

Carosati

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Blazar S5 0716+714 is well-known for its short-term variability, down to intra-day time-scales. We here present the 2-min cadence optical light curve obtained by the TESS space telescope in 2019 December – 2020 January and analyse the object fast variability with unprecedented sampling. Supporting observations by the Whole Earth Blazar Telescope Collaboration in B, V, R, and I bands allow us to investigate the spectral variability during the TESS pointing. The spectral analysis is further extended in frequency to the UV and X-ray bands with data from the Neil Gehrels Swift Observatory. We develop a new method to unveil the shortest optical variability time-scales. This is based on progressive de-trending of the TESS light curve by means of cubic spline interpolations through the binned fluxes, with decreasing time bins. The de-trended light curves are then analysed with classical tools for time-series analysis (periodogram, auto-correlation and structure functions). The results show that below 3 d there are significant characteristic variability time-scales of about 1.7, 0.5, and 0.2 d. Variability on time-scales $\lesssim 0.2$ d is strongly chromatic and must be ascribed to intrinsic energetic processes involving emitting regions, likely jet sub-structures, with dimension less than about 10−3 pc. In contrast, flux changes on time-scales $\gtrsim 0.5$ d are quasi-achromatic and are probably due to Doppler factor changes of geometric origin.

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“…The typical approach to search for periodicity at -ray energies in blazars is to analyze a limited sample of a few blazars and apply two or three time-series algorithms [e.g., 3,21]. In [10], we developed a pipeline to perform a search for periodicities in hundreds of blazars. As a result, we discovered 24 blazars with a tentative periodicity (with significance < 5 ).…”

Section: < 50% Upper-limitsmentioning

confidence: 99%

“…In this contribution, we re-analyze the 24 periodicity candidates that were presented in [10]. In [10], this sample was analyzed using nine years of Fermi-Large Area Telescope (LAT) observations [2]. Now, we employ twelve years of Fermi-LAT telescope time, from August 2008 until December 2020.…”

Section: Blazar Samplementioning

confidence: 99%

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Building a robust sample of Fermi-LAT blazars that exhibit periodic gamma-ray emission

Peñil¹,

Ajello²,

Buson³

et al. 2021

Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)

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Blazars can show variability on a wide range of timescales. However, the search for periodicity in the -ray emission of blazars remains an on-going challenge. This contribution will show the results obtained when a systematic pipeline is used to implement ten well-established methods to search for periodicity. We analyze the most promising candidates selected from our previous work, extending the Fermi-LAT light curves over three more years, for a total telescope time of twelve years. These improvements have allowed us to build the first sample of blazars that display a periodicity detected at a significance > 5 . Finally, we will discuss the potential origins for the periodic behavior observed in blazars.

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Systematic Search for γ-Ray Periodicity in Active Galactic Nuclei Detected by the Fermi Large Area Telescope

Cited by 72 publications

References 54 publications

Ornstein-Uhlenbeck parameter extraction from light curves of Fermi-LAT observed blazars

Ornstein-Uhlenbeck parameter extraction from light curves of Fermi-LAT observed blazars

The dual nature of blazar fast variability: Space and ground observations of S5 0716+714

Building a robust sample of Fermi-LAT blazars that exhibit periodic gamma-ray emission

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