Optical flux and spectral variability of blazars

Gaur, Haritma; Gupta, Alok C.; Strigachev, A.; Bachev, R.; Semkov, E.; Wiita, Paul J.; Peneva, S.; Boeva, S.; Slavcheva-Mihova, L.; Mihov, B.; Latev, G.; Pandey, U. S.

doi:10.1111/j.1365-2966.2012.21583.x

Cited by 74 publications

(62 citation statements)

References 149 publications

(226 reference statements)

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“…The observations were carried out at seven telescopes in Bulgaria, Greece, Georgia, and India. The telescopes and cameras that were involved in these observations are described in detail in Gaur et al (2012b).…”

Section: Optical Datamentioning

confidence: 99%

Optical and radio variability of BL Lacertae

Gaur

Gupta

Bachev

et al. 2015

A&A

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Context. We extensively observed the prototype blazar, BL Lacertae, in optical and radio bands during an active phase in the period 2010-2013 when the source showed several prominent outbursts. We searched for possible correlations and time lags between the optical and radio band flux variations using multi-frequency data to learn about the mechanisms producing variability. Aims. During an active phase of BL Lacertae, we searched for possible correlations and time lags between multi-frequency light curves of several optical and radio bands. We tried to estimate any possible variability timescales and inter-band lags in these bands. Methods. We performed optical observations in B, V, R, and I-bands from seven telescopes in Bulgaria, Georgia, Greece, and India and obtained radio data at 36.8, 22.2, 14.5, 8, and 4.8 GHz frequencies from three telescopes in Crimea, Finland, and USA. Results. Significant cross-correlations between optical and radio bands are found in our observations with a delay of cm-fluxes with respect to optical bands of ∼250 days. The optical and radio light curves do not show any significant timescales of variability. BL Lacertae showed many optical "mini-flares" on short timescales. Variations on longer term timescales are mildly chromatic with the superposition of many strong optical outbursts. In radio bands, the amplitude of variability is frequency dependent. Flux variations at higher radio frequencies lead the lower frequencies by days or weeks. Conclusions. The optical variations are consistent with being dominated by a geometric scenario where a region of emitting plasma moves along a helical path in a relativistic jet. The frequency dependence of the variability amplitude supports an origin of the observed variations intrinsic to the source.

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Section: Optical Datamentioning

confidence: 99%

Optical and radio variability of BL Lacertae

Gaur

Gupta

Bachev

et al. 2015

A&A

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“…Alternatively, BL Lacs are often observed in bluer when brighter states, likely a result of significantly less radiative cooling of highly accelerated electrons off an under-luminous or non-existent accretion disk (Massaro et al 1998;Villata et al 2002;Vagnetti et al 2003;Gu & Ai 2011a;Gaur et al 2012). These observations have been extrapolated to represent the "typical" behavior of FSRQs and BL Lacs.…”

Section: Introductionmentioning

confidence: 99%

A Consolidated Framework of the Color Variability in Blazars: Long-term Optical/Near-infrared Observations of 3C 279

Isler

Urry

Coppi

et al. 2017

ApJ

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We evaluate the optical/near-infrared (OIR) color variability of 3C 279 in both γ-ray flaring and non-flaring states over 7-year timescales using the Small and Medium Aperture Research Telescope System (SMARTS ) in Cerro Tololo, Chile and γ-ray fluxes obtained from the Fermi γ-ray Space Telescope. This observing strategy differs from previous blazar color variability studies in two key ways: 1) the reported color variability is assessed across optical through near-infrared wavelengths, and 2) the color variability is assessed over timescales significantly longer than an individual flare or ground-based observing season. We highlight 3C 279 because of its complex color variability, which is difficult to reconcile with the simple 'redder when brighter' behavior often associated with Flat Spectrum Radio Quasar (FSRQ) color variability. We suggest that the observed OIR color changes depend on a combination of the jet and disk emission. We parametrize this behavior in terms of a single variable, ζ m n , representing a smooth transition from disk-dominated, to a mixed contribution, to a jet-dominated system, which provides an explanation of the long-term OIR color variability in the same blazar over time. This suggests a general scheme that could apply to OIR color variability in other blazars.

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“…The colour or spectral behaviour of this blazar has been studied by number of authors (Ghisellini et al 1997;Raiteri et al 2003;Gu et al 2006;Rani et al 2010) on various timescales but is still a subject of debate. Some authors found a bluer-when-brighter (BWB) chromatism (e.g., Wu et al 2005;Gaur et al 2012); others claimed the opposite (e.g., Ghisellini et al 1997), or no colour change with brightness even in flaring state (e.g., Stalin et al 2006). Another intriguing result pointed out by Qian et al (1996) and Wagner et al (1996) is that the radio spectral index of this source was found to correlate with the intranight optical variations, thus giving further evidence for correlated variability in the radio and optical ranges as noted earlier by Quirrenbach et al (1991).…”

Section: Introductionmentioning

confidence: 99%

Multiband optical variability of the blazar S5 0716+714 in outburst state during 2014–2015

Agarwal

Gupta

Bachev

et al. 2015

Mon. Not. R. Astron. Soc.

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We analyzed the multi-band optical behaviour of the BL Lacertae object, S5 0716+714, during its outburst state from 2014 November -2015 March. We took data on 23 nights at three observatories, one in India and two in Bulgaria, making quasi-simultaneous observations in B, V, R, and I bands. We measured multi-band optical fluxes, colour and spectral variations for this blazar on intraday and short timescales. The source was in a flaring state during the period analyzed and displayed intense variability in all wavelengths. R band magnitude of 11.6 was attained by the target on 18 Jan 2015, which is the brightest value ever recorded for S5 0716+714. The discrete correlation function method yielded good correlation between the bands with no measurable time lags, implying that radiation in these bands originate from the same region and by the same mechanism. We also used the structure function technique to look for characteristic timescales in the light curves. During the times of rapid variability, no evidence for the source to display spectral changes with magnitude was found on either of the timescales. The amplitude of variations tends to increase with increasing frequency with a maximum of ∼ 22% seen during flaring states in B band. A mild trend of larger variability amplitude as the source brightens was also found. We found the duty cycle of our source during the analyzed period to be ∼ 90%. We also investigated the optical spectral energy distribution of S5 0716+714 using B, V, R, and I data points for 21 nights. We briefly discuss physical mechanisms most likely responsible for its flux and spectral variations.

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Optical flux and spectral variability of blazars

Cited by 74 publications

References 149 publications

Optical and radio variability of BL Lacertae

Optical and radio variability of BL Lacertae

A Consolidated Framework of the Color Variability in Blazars: Long-term Optical/Near-infrared Observations of 3C 279

Multiband optical variability of the blazar S5 0716+714 in outburst state during 2014–2015

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