Optical Variability of TeV Blazars on long time-scales

Gaur, Haritma; Gupta, Alok C.; Bachev, R.; Strigachev, A.; Semkov, E.; Wiita, Paul J.; Kurtanidze, O. M.; Darriba, A.; Damljanović, G.; Chanishvili, R. G.; Ibryamov, S.; Kurtanidze, S. O.; Nikolashvili, M. G.; Sigua, L. A.; Vince, O.

doi:10.1093/mnras/stz322

Cited by 23 publications

(9 citation statements)

References 67 publications

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“…The method is based on plots of (quasi)simultaneous flux densities in different colour bands and the construction of the relative continuum spectrum based on the slopes of the sets of fluxflux relations thus obtained. This method was successfully applied for the quantitative analysis of the synchrotron radiation of several blazars, for example, 0235+164 (Hagen-Thorn et al 2008); 3C 279, BL Lac, and CTA 102 (Larionov et al , 2010(Larionov et al , 2016b; 3C 454.3 (Jorstad et al 2010); and 3C 66a, S4 0954+65, and BL Lac (Gaur et al 2019).…”

Section: Flux and Colour Evolutionmentioning

confidence: 99%

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Ларионов

Jorstad

Marscher

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We report the results of decade-long (2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) γ-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ-ray light curves correlate well, with no delay > ∼ 3 hours, implying general co-spatiality of the emission regions. The γ-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz VLBA images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain γ-ray variability on very short time scales. The Mg II emission line flux in the 'blue' and 'red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands we find progressive delays of the most prominent light curve maxima with decreasing frequency, as expected from the frequency dependence of the τ = 1 surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at ∼ 5 GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.

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Section: Flux and Colour Evolutionmentioning

confidence: 99%

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Ларионов

Jorstad

Marscher

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…In particular, at the synchrotron frequencies, within the simplest scenario of single-zone emission models with homogeneous magnetic field distributions, clear patterns between the spectral index and the total intensity are predicted, i.e., a "spectral hysteresis", depending on the relative lengths of the radiative cooling timescale and the escape timescale of the accelerated particles from the emission zone (e.g., Kirk et al 1998). A significant fraction of long-term multiband flux monitoring studies have revealed bluer-when-brighter trends for BL Lac objects but frequently redder-whenbrighter trends for FSRQs (Gu et al 2006;Osterman Meyer et al 2009;Rani et al 2010;Hao et al 2010;Ikejiri et al 2011;Bonning et al 2012;Sandrinelli et al 2014;Meng et al 2018;Li et al 2018;Gupta et al 2019) while 'achromatic' flux variability (no colour evolution, Gaur et al 2019;Bonning et al 2012;Stalin et al 2006), and erratic patterns (Wierzcholska et al 2015) have also been reported. It has been argued that particles accelerated to higher energies are injected at the emission zone before being cooled radiatively in BL Lac sources leading to their overall SEDs being bluer-when-brighter; however, the 'redder' and more variable jet-component can overwhelm the 'bluer' contribution from the accretion disc, leading to redder-when-brighter trends for FSRQ type sources (Gu et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Multiband optical flux density and polarization microvariability study of optically bright blazars

Pasierb

Goyal

Ostrowski

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the results of flux density, spectral index, and polarization intra-night monitoring studies of a sample of eight optically bright blazars, carried out by employing several small to moderate aperture (0.4 m to 1.5 m diameter) telescopes fitted with CCDs and polarimeters located in Europe, India, and Japan. The duty cycle of flux variability for the targets is found to be ∼ 45 percent, similar to that reported in earlier studies. The computed two-point spectral indices are found to be between 0.65 to 1.87 for our sample, comprised of low-and intermediate frequency peaked blazars, with one exception; they are also found to be statistically variable for about half the instances where 'confirmed' variability is detected in flux density. In the analysis of the spectral evolution of the targets on hourly timescale, a counter-clockwise loop (soft-lagging) is noted in the flux-spectral index plane on two occasions, and in one case a clear spectral flattening with the decreasing flux is observed. In our data set, we also observe a variety of flux-polarization degree variability patterns, including instances with a relatively straightforward anti-correlation, correlation, or counterclockwise looping. These changes are typically reflected in the flux-polarization angle plane: the anti-correlation between the flux and polarization degree is accompanied by an anti-correlation between the polarization angle and flux, while the counterclockwise flux-PD looping behaviour is accompanied by a clockwise looping in the flux-polarization angle representation. We discuss our findings in the framework of the internal shock scenario for blazar sources.

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“…However the correlation between colour and brightness in blazars is highly debated in literature. Reports available in literature indicate that among blazars, in BL Lacs the colour becomes bluer with increasing brightness (BWB; D' Amicis et al 2002;Vagnetti et al 2003;Fiorucci et al 2004;Meng et al 2018;Gaur et al 2019), while in FSRQs the colour becomes redder with increasing brightness (RWB; Bonning et al 2012;Sarkar et al 2019). Such a distinct colour magnitude relation between FSRQs and BL Lacs lead to speculate that the jets of FSRQs and BL Lacs are fundamentally different.…”

Section: Colour Variabilitymentioning

confidence: 98%

Long term optical and infrared variability characteristics of Fermi Blazars

Safna,

Stalin,

Rakshit

et al. 2020

Preprint

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We present long term optical and near infrared flux variability analysis of 37 blazars detected in the γ-ray band by the Fermi Gamma-Ray Space Telescope. Among them, 30 are flat spectrum radio quasars (FSRQs) and 7 are BL Lac objects (BL Lacs). The photometric data in the optical (BVR) and infrared (JK) bands were from the Small and Moderate Aperture Research Telescope System acquired between 2008−2018. From cross-correlation analysis of the light curves at different wavelengths, we did not find significant time delays between variations at different wavelengths, except for three sources, namely PKS 1144−379, PKS B1424−418 and 3C 273. For the blazars with both B and J-band data, we found that in a majority of FSRQs and BL Lacs, the amplitude of variability (σ m ) in the J-band is larger than B-band consistent with the dominance of the non-thermal jet over the thermal accretion disc component. Considering FSRQs and BL Lacs as a sample, there are indications of σ m to increase gradually towards longer wavelengths in both, however, found to be statistically significant only between B and J-bands in FSRQs. In the B−J v/s J colour magnitude diagram, we noticed complicated spectral variability patterns. Most of the objects showed a redder when brighter (RWB) behaviour. Few objects showed a bluer when brighter (BWB) trend, while in some objects both BWB and RWB behaviours were noticed. These results on flux and colour characteristics indicate that the jet emission of FSRQs and BL Lacs is indistinguishable.

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Optical Variability of TeV Blazars on long time-scales

Cited by 23 publications

References 67 publications

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Multiband optical flux density and polarization microvariability study of optically bright blazars

Long term optical and infrared variability characteristics of Fermi Blazars

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