Lognormal variability in BL Lacertae

Giebels, B.; Degrange, B.

doi:10.1051/0004-6361/200912303

Cited by 71 publications

(71 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The description of the rapid variability of a TeV blazar as a random stationary process must be taken into account by time-dependent blazar models. For PKS 2155−304 the evidence of this log-normality has been found very recently in X-rays (Giebels & Degrange 2009) and as previously mentioned, X-ray binaries and Seyfert galaxies also show lognormal variability, which is thought to originate from the accretion disk (M c Hardy et al 2004;Lyubarskii et al 1997;Arévalo & Uttley 2006), suggesting a connection between the disk and the jet. This variability behavior should therefore be searched for in existing blazar light curves, independently of the observed wavelength.…”

Section: Discussionmentioning

confidence: 60%

VHEγ-ray emission of PKS 2155–304: spectral and temporal variability

Abramowski¹,

Acero²,

Aharonian³

et al. 2010

A&A

Self Cite

100

View full text Add to dashboard Cite

Context. Observations of very high-energy γ-rays from blazars provide information about acceleration mechanisms occurring in their innermost regions. Studies of variability in these objects lead to a better understanding of the mechanisms in play. Aims. To investigate the spectral and temporal variability of VHE (>100 GeV) γ-rays of the well-known high-frequency-peaked BL Lac object PKS 2155−304 with the HESS imaging atmospheric Cherenkov telescopes over a wide range of flux states. Methods. Data collected from 2005 to 2007 were analyzed. Spectra were derived on time scales ranging from 3 years to 4 min. Light curve variability was studied through doubling timescales and structure functions and compared with red noise process simulations. Results. The source was found to be in a low state from 2005 to 2007, except for a set of exceptional flares that occurred in July 2006. The quiescent state of the source is characterized by an associated mean flux level of (4.32 ± 0.09 stat ± 0.86 syst ) × 10 −11 cm −2 s −1 above 200 GeV, or approximately 15% of the Crab Nebula, and a power-law photon index of Γ = 3.53 ± 0.06 stat ± 0.10 syst . During the flares of July 2006, doubling timescales of ∼2 min are found. The spectral index variation is examined over two orders of magnitude in flux, yielding different behavior at low and high fluxes, which is a new phenomenon in VHE γ-ray emitting blazars. The variability amplitude characterized by the fractional rms F var is strongly energy-dependent and is ∝E 0.19±0.01 . The light curve rms correlates with the flux. This is the signature of a multiplicative process that can be accounted for as a red noise with a Fourier index of ∼2. Conclusions. This unique data set shows evidence of a low-level γ-ray emission state from PKS 2155−304 that possibly has a different origin than the outbursts. The discovery of the light curve lognormal behavior might be an indicator of the origin of aperiodic variability in blazars.

show abstract

Section: Discussionmentioning

confidence: 60%

VHEγ-ray emission of PKS 2155–304: spectral and temporal variability

Abramowski¹,

Acero²,

Aharonian³

et al. 2010

A&A

Self Cite

100

View full text Add to dashboard Cite

show abstract

“…In black-hole-powered sources like Seyfert galaxies and X-ray binaries, lognormality is widely believed to be a result of fluctuations in the accretion disk (Uttley et al 2005;McHardy 2008; see also Gaskell 2004). Thus, a lognormal flux distribution in blazars may be an imprint of modulation in the disk, connecting jet to disk activity (McHardy 2008;Giebels & Degrange 2009). Additionally, a lognormal distribution is also expected for plasma ejection triggered by local magnetic reconnections (see, e.g., Aoki et al 2003), but contributes negligibly to blazars emission (Kadowaki et al 2015).…”

Section: Discussionmentioning

confidence: 99%

Evidence for Two Lognormal States in Multi-Wavelength Flux Variation of FSRQ PKS 1510-089

Kushwaha

Chandra

Misra

et al. 2016

ApJL

View full text Add to dashboard Cite

We present a systematic characterization of multi-wavelength emission from blazar PKS 1510-089 using wellsampled data at near-infrared (NIR), optical, X-ray, and γ-ray energies. The resulting flux distributions, except at X-rays, show two distinct lognormal profiles corresponding to a high and a low flux level. The dispersions exhibit energy-dependent behavior except in the LAT γ-ray and optical B-band. During the low level flux states, it is higher toward the peak of the spectral energy distribution, with γ-ray being intrinsically more variable followed by IR and then optical, consistent with mainly being a result of varying bulk Lorentz factor. On the other hand, the dispersions during the high state are similar in all bands except the optical B-band, where thermal emission still dominates. The centers of distributions are a factor of ∼4 apart, consistent with anticipation from studies of extragalactic γ-ray background with the high state showing a relatively harder mean spectral index compared to the low state.

show abstract

“…We then thus checked the consistency of the distributions with a lognormal as is normally inferred for RQAGNs, GXBs and even blazars (Kushwaha et al 2016;H.E.S.S. Collaboration et al 2010;Giebels & Degrange 2009). The skewness of the logarithm of the fluxes was also computed, which was found to be closer to zero for the three blazars, but significantly large for the radio-galaxy.…”

Section: Flux Distribution and Effect Of Photon Statisticsmentioning

confidence: 97%

Gamma-Ray Flux Distribution and Nonlinear Behavior of Four LAT Bright AGNs

Kushwaha

Sinha

Misra

et al. 2017

ApJ

View full text Add to dashboard Cite

We present a statistical characterization of the γ-ray emission from the four Fermi -LAT sources: FR I radio galaxy NGC 1275, BL Lac Mrk 421, FSRQs B2 1520+31 and PKS 1510-089 detected almost continuously over a time integration of 3-days between August 2008 -October 2015. The observed flux variation is large, spanning 2 orders of magnitude between the extremes except for Mrk 421. We compute the flux distributions and compare with Gaussian and lognormal ones. We find that the 3 blazars have distribution consistent with a lognormal, suggesting that the variability is of a non-linear, multiplicative nature. This is further supported by the computation of the flux-rms relation, which is observed to be linear for the 3 blazars. However, for NGC 1275, the distribution does not seem to be represented either by a lognormal or a Gaussian, while its flux-rms relation is still found to be linear. We also compute the power spectra, which suggest the presence of a break, but are consistent with typical scale-free power-law shot noise. The results are broadly consistent with the statistical properties of the magnetic reconnection powered minijets-in-a-jet model. We discuss other possible scenarios and implications of these observations on jet processes and connections with the central engine.

show abstract

Lognormal variability in BL Lacertae

Cited by 71 publications

References 13 publications

VHEγ-ray emission of PKS 2155–304: spectral and temporal variability

VHEγ-ray emission of PKS 2155–304: spectral and temporal variability

Evidence for Two Lognormal States in Multi-Wavelength Flux Variation of FSRQ PKS 1510-089

Gamma-Ray Flux Distribution and Nonlinear Behavior of Four LAT Bright AGNs

Contact Info

Product

Resources

About