Short-term optical variability of high-redshift quasi-stellar objects

Bachev, R.; Strigachev, A.; Semkov, E.

doi:10.1111/j.1365-2966.2005.08708.x

Cited by 33 publications

(37 citation statements)

References 38 publications

(48 reference statements)

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“…Gupta et al 2008) which could in turn shed some light on the evolution process in AGNs (Barth 2002;Fan 2003). The shortest timescale of variability is associated with the light crossing time of the variable region, which in AD based models is directly proportional to the BH masses (Bachev, Strigachev, & Semkov 2005). The probability of detecting variability in blazars increases with the duration of observations.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…The photometric errors indicated in the next section are the theoretical ones; see e.g. Bachev et al (2005) and the references therein and for possible caveats. Fig.…”

Section: Observations and Reductionsmentioning

confidence: 99%

Violent intranight optical variability of the blazar S4 0954+65 during its unprecedented 2015 February outburst

Bachev¹

2015

Monthly Notices of the Royal Astronomical Society: Letters

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In this letter we present results from intra-night monitoring in three colors (BRI) of the blazar S4 0954+65 during its recent (2015 February) unprecedented high state. We find violent variations on very short time scales, reaching magnitude change levels of 0.1-0.2 mag/h. On some occasions, changes of ∼0.1 mag are observed even within ∼10 min. During the night of 14.02.2015 an exponential drop of ∼0.7 magnitudes is detected for about 5 hours. Cross-correlation between the light curves does not reveal any detectable wavelength-dependent time delays, larger than ∼5 min. Color changes "bluer-when-brighter" are observed on longer time scales. Possible variability mechanisms to explain the observations are discussed and a preference to the geometrical one is given.

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“…The proposed technique of microlensing-aided reverberation mapping aims at taking advantage of this effect to measure the time lag between the continuum and broad line variations. Our method is not conceptually very different from photometric reverberation mapping (Haas et al 2011;Chelouche & Daniel 2012;Chelouche & Zucker 2013;Pozo Nuñez et al 2012;Edri et al 2012;Zu et al 2014;Bachev et al 2014). In that case, multi-band photometry is used to disentangle the flux of the continuum and of the BLR, while our technique can already be applied to singleband data.…”

Section: Introductionmentioning

confidence: 99%

Imprints of the quasar structure in time-delay light curves: Microlensing-aided reverberation mapping

Sluse¹,

Tewes²

2014

A&A

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Owing to the advent of large area photometric surveys, the possibility to use broad band photometric data, instead of spectra, to measure the size of the broad line region of active galactic nuclei, has raised a large interest. We describe here a new method using time-delay lensed quasars where one or several images are affected by microlensing due to stars in the lensing galaxy. Because microlensing decreases (or increases) the flux of the continuum compared to the broad line region, it changes the contrast between these two emission components. We show that this effect can be used to effectively disentangle the intrinsic variability of those two regions, offering the opportunity to perform reverberation mapping based on single band photometric data. Based on simulated light curves generated using a damped random walk model of quasar variability, we show that measurement of the size of the broad line region can be achieved using this method, provided one spectrum has been obtained independently during the monitoring. This method is complementary to photometric reverberation mapping and could also be extended to multi-band data. Because the effect described above produces a variability pattern in difference light curves between pairs of lensed images which is correlated with the time-lagged continuum variability, it can potentially produce systematic errors in measurement of time delays between pairs of lensed images. Simple simulations indicate that time-delay measurement techniques which use a sufficiently flexible model for the extrinsic variability are not affected by this effect and produce accurate time delays.

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Short-term optical variability of high-redshift quasi-stellar objects

Cited by 33 publications

References 38 publications

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

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

Violent intranight optical variability of the blazar S4 0954+65 during its unprecedented 2015 February outburst

Imprints of the quasar structure in time-delay light curves: Microlensing-aided reverberation mapping

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