Gamma-Ray Astrophysics in the Time Domain

Rieger, F.

doi:10.3390/galaxies7010028

Cited by 39 publications

(31 citation statements)

References 91 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The sources form a dominant group of sources that prominently shine in the γ-ray band: the recent fourth Fermi Large Area Telescope source catalog (4FGL) contains about 60% of the γ-detected sources as the blazar class (The Fermi-LAT collaboration 2019). Therefore, study of γ-ray emission from blazar can compliment similar studies on the origin and propagation of high energy emission in the Universe (see Rieger 2019;Madejski, & Sikora 2016).…”

Section: Introductionmentioning

confidence: 63%

The Nature of γ-Ray Variability in Blazars

Bhatta

Dhital

2020

ApJ

View full text Add to dashboard Cite

We present an in-depth and systematic analysis of a sample of 20 powerful blazars, including 12 BL Lacs and 8 flat spectrum radio quasars, utilizing Fermi/LAT observations from the period 2008-2018 using various analysis tools such as flux distribution, symmetry analysis, and time series analysis. Results show that blazars with steeper γ-ray spectral indexes are found to be more variable; and the γ-ray flux distribution closely resemble both normal and lognormal probability distribution functions. The statistical variability properties of the sources as studied by power spectral density analysis are consistent with flicker noise (P (ν) ∝ 1/ν) -an indication of long-memory processes at work. Statistical analysis of the distribution of flux rise and decay rates in the light curves of the sources, aimed at distinguishing between particle acceleration and energy dissipation timescales, counter-intuitively suggests that both kinds of rates follow a similar distribution and the derived mean variability timescales are in the order of a few weeks. The corresponding emission region size is used to constrain location of γ-ray production sites in the sources to be a few parsecs. Additionally, using Lomb-Scargle periodogram aided with extensive Monte Carlo simulations, we detected year timescale quasi-periodic oscillations in the sources S5 0716+714, Mrk 421, ON +325, PKS 1424-418 and PKS 2155-304; and the detection significance was computed taking proper account of the red-noise and other artifacts inherent in the observations. We explain our results in the light of current blazar models with relativistic shocks propagating down the jet viewed close to the line of sight.

show abstract

Section: Introductionmentioning

confidence: 63%

The Nature of γ-Ray Variability in Blazars

Bhatta

Dhital

2020

ApJ

View full text Add to dashboard Cite

show abstract

“…Shorter timescales explained with a SBBH model would imply very close binary systems. The detection of these systems is very improbable due to their very short lifetime (Rieger 2019).…”

Section: Discussionmentioning

confidence: 99%

Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38

Otero-Santos

Acosta–Pulido

González

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We report on quasi-periodic variability found in two blazars included in the Steward Observatory Blazar Monitoring data sample: the BL Lac object 3C 66A and the Flat Spectrum Radio Quasar B2 1633+38. We collect optical photometric and polarimetric data in V and R bands of these sources from different observatories: St. Petersburg University, Crimean Astrophysical Observatory, WEBT-GASP, Catalina Real-Time Transient Survey, Steward Observatory, STELLA Robotic Observatory and Katzman Automatic Imaging Telescope. In addition, an analysis of the γ-ray light curves from Fermi-LAT is included. Three methods are used to search for any periodic behaviour in the data: the Z-transform Discrete Correlation Function, the Lomb-Scargle periodogram and the Weighted Wavelet Z-transform. We find evidences of possible quasiperiodic variability in the optical photometric data of both sources with periods of ∼3 years for 3C 66A and ∼1.9 years for B2 1633+38, with significances between 3σ and 5σ. Only B2 1633+38 shows evidence of this behaviour in the optical polarized data set at a confidence level of 2σ-4σ. This is the first reported evidence of quasi-periodic behaviour in the optical light curve of B2 1633+38. Also a hint of quasi-periodic behaviour is found in the γ-ray light curve of B2 1633+38 with a confidence level 2σ, while no periodicity is observed for 3C 66A in this energy range. We propose different jet emission models that could explain the quasi-periodic variability and the differences found between these two sources.

show abstract

“…The variations on short timescales provide an additional challenge at the TeVγ-ray photon energies, as large jet bulk Lorentz factors (Γ) > 30-50 is needed to overcome photon opacity arguments [10,11], which are rather too extreme to be reconciled with the currently-favored models for the jet formation in blazar sources [12]. Moreover, the statistical properties of blazar light curves (from radio to γ-ray energies), in particular, the simple power-law shape of variability power spectral densities (PSDs; defined as P(ν k )∝ ν −β k , where ν k is the temporal frequency, and β 1-3 is the slope), indicate that the variability is generated by correlated noise-like processes on timescales ranging from decades to minutes (see, for a recent review, [13,14]). Specifically, the variations at synchrotron and IC energies seem to exhibit different statistical characteristics; one following a red/damped-noise process (β ∼ 2), while the other following a pink/long-memory process (β ∼ 1) (see [15] and the references therein).…”

Section: Introductionmentioning

confidence: 99%

PKS 2155-304: A Case Study of Blazar Variability Power Spectrum at the Highest Energies and on the Longest Timescales

Goyal

2019

Galaxies

View full text Add to dashboard Cite

We present the results of our Power Spectral Density (PSD) analysis for the BL Lac object PKS 2155−304, utilizing the nightly-binned long-term light curve from the decade-long monitoring, as well as the minute-binned intra-night light curve from the High Energy Stereoscopic Survey (H.E.S.S.; >200 GeV). The source is unique for exhibiting the shortest flux-doubling timescale at Very High Energy (VHE) among its class and thus provides a rare opportunity to study the particle acceleration on the smallest spatial scales in blazar jets. The light curves are modeled in terms of the Continuous-Time Auto-Regressive Moving Average (CARMA) process. The combined long-term and intra-night PSD extends up to ∼6 decades in the temporal frequency range; unprecedented at the TeV energies for a blazar source. Our systematic approach reveals that PKS 2155−304 shows, on average, a complex shape of variability power spectrum, with more variability power on longer timescales. The long-term variability is best modeled by the CARMA(2,1) process, while the intra-night variability is modeled by a CARMA(1,0) process. We note that the CARMA(1,0) process refers to an Ornstein–Uhlenbeck process where the power-law PSD slope (PSD varies as a function of variability frequency to the power of the negative slope) changes from two to zero, above a certain “characteristic/relaxation” timescale. Even though the derived power spectrum of the intra-night light curve did not reveal a flattening, we speculate such relaxation must occur on timescales longer than a few hours for the source.

show abstract

Gamma-Ray Astrophysics in the Time Domain

Cited by 39 publications

References 91 publications

The Nature of γ-Ray Variability in Blazars

The Nature of γ-Ray Variability in Blazars

Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38

PKS 2155-304: A Case Study of Blazar Variability Power Spectrum at the Highest Energies and on the Longest Timescales

Contact Info

Product

Resources

About