The longer optical time scales of a large sample of quasars

Smith, Alex; Nair, A. D.; Leacock, R. J.; Clements, S. D.

doi:10.1086/116442

Cited by 49 publications

(54 citation statements)

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“…Other recent optical observations are reported by Cutri et al (1985), Corso et al (1987), Courvoisier et al (1987), Smith et al (1987), Sillanapää et al (1991), Valtaoja et al (1991b) and Takalo et al (1992). Smith et al (1993) studied the longer optical time scale of this object, but they found no base level changes during 16.5 years.…”

Section: +023 (3c 273mentioning

confidence: 67%

Automatic optical monitoring of 10 blazars

Fiorucci

Tosti

1996

Astron. Astrophys. Suppl. Ser.

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Abstract. -We report the BV RcIc data for 10 blazars observed in the first phase of a long-term photometric monitoring program of about 30 objects. The observations were carried out with a 0.40-m automatic imaging telescope, recently developed by our group at the Perugia University Observatory. During our period of observation 1215+303 and 1424+240 were at their highest values of magnitude, while 0754+100 and 0829+043 displayed large amplitude flares. We further report optical data of Mrk 501 during the same period in which TeV γ-rays were detected by the Whipple Observatory.

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Section: +023 (3c 273mentioning

confidence: 67%

Automatic optical monitoring of 10 blazars

Fiorucci

Tosti

1996

Astron. Astrophys. Suppl. Ser.

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“…If the nucleus of the radio quasar contains an active BBH system, then the astrometric precision will be obviously limited by the size of this system. Finally it is known that photometric variabilty can occur on time scales longer than our observation time span (Smith et al 1993). These very long photometric variations could be due to the larger regions (dust torus, host galaxy) and could have an impact at the level of some mas on the astrometry of the targets.…”

Section: Conclusion and Prospectsmentioning

confidence: 88%

“…If α = 1, shot noise dominates, toward flatter slopes (α = 0) where flicker noise becomes more important. When a light curve contains a periodic signal, the structure function rises to a maximum at half the period and then falls to a minimum for the period of the signal (Smith et al 1993).…”

Section: Structure Functionsmentioning

confidence: 99%

Long-termRandV-band monitoring of some suitable targets for the link between ICRF and the futureGaiacelestial reference frame

Taris

Andrei

Roland

et al. 2016

A&A

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Context. The Gaia astrometric mission of the European Space Agency was launched on December 2013. It will provide a catalog of 500 000 quasars. Some of these targets will be chosen to build an optical reference system that will be linked to the International Celestial Reference Frame (ICRF). The astrometric coordinates of these sources will have roughly the same uncertainty at both optical and radio wavelengths, and it is then mandatory to observe a common set of targets to build the link. In the ICRF, some targets have been chosen because of their pointlikeness. They are quoted as defining sources, and they ensure very good uncertainty about their astrometric coordinates. At optical wavelengths, a comparable uncertainty could be achieved for targets that do not exhibit strong astrophysical phenomena, which is a potential source of photocenter flickering. A signature of these phenomena is a magnitude variation at optical wavelengths. Aims. The goal of this work is to present the time series of 14 targets suitable for the link between the ICRF and the future Gaia Celestial Reference Frame. The observations have been done systematically by robotic telescopes in France and Chile once every two nights since 2011 and in two filters. These time series are analyzed to search for periodic or quasi-periodic phenomena that must be taken into account when computing the uncertainty about the astrometric coordinates. Methods. Two independent methods were used in this work to analyze the time series. We used the CLEAN algorithm to compare the frequency obtained to those given by the Lomb-Scargle method. It avoids misinterpreting the frequency peaks given in the periodograms. Results. For the 14 targets we determine some periods with a confidence level above 90% in each case. Some of the periods found in this work were not previously known. For the others, we did a comparative study of the periods previously studied by others and always confirm their values. All the periods given by the two methods are in good agreement with the difference always below 7.9% in the worst case. Finally we also present the structure functions for our two sets of objects (BL Lac and Seyfert galaxies). Conclusions. For all but one target, we find variations that could be the signature of periodic or quasi-periodic phenomena. Our time series could allow to bring some constraints on astrophysical models that could explain such variations. Binary black hole system, instabilities in the jet or in the accretion disk, changes in the torus structure are some of these astrophysical phenomena. They must be kept in mind when evaluating the uncertainty about the astrometric position of the targets suitable for the link between reference systems in a conservative way.

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“…Most objects were collected from Teerikorpi et al (2000), as well as Maccacaro et al (1987) and inspections of light curves in Smith et al (1993). The observations were performed under the Observatório Nacional/MCT, Brasil, telescope time contracted to ESO at the Max Planck 2.2 m telescope at La Silla, Chile.…”

Section: Observationsmentioning

confidence: 99%

Photocentric variability of quasars caused by variations in their inner structure: consequences forGaiameasurements

Popovic

Jovanović

Antón

et al. 2012

A&A

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Context. We study the photocenter position variability caused by variations in the quasar inner structure. We consider the variability in the accretion disk emissivity and torus structure variability caused by the different illumination by the central source. We discuss the possible detection of these effects by Gaia. Observations of the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS J162011+1724327 have been reported and discussed. Aims. For variations in the quasar inner structure, we explore how much this effect can affect the position determination and whether it can (or not) be detected with the Gaia mission. Methods. We use models of (a) a relativistic disk, including the perturbation that can increase the brightness of part of the disk, and consequently offset the photocenter position, and (b) a dusty torus that absorbs and re-emits the incoming radiation from the accretion disk (central continuum source). We estimate the value of the photocenter offset caused by these two effects. Results. We found that perturbations in the inner structure can cause a significant offset to the photocenter. This offset depends on the characteristics of both the perturbation and accretion disk and on the structure of the torus. In the case of the two considered QSOs, the observed photocenter offsets cannot be explained by variations in the accretion disk and other effects should be considered. We discuss the possibility of exploding stars very close to the AGN source, and also that there are two variable sources at the center of these two AGNs that may indicate a binary supermassive black hole system on a kpc (pc) scale. Conclusions. The Gaia mission seems to be very promising, not only for astrometry, but also for exploring the inner structure of AGNs. We conclude that variations in the quasar inner structure can affect the observed photocenter (by up to several mas). There is a chance to observe such an effect in the case of bright and low-redshift QSOs.

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The longer optical time scales of a large sample of quasars

Cited by 49 publications

References 0 publications

Automatic optical monitoring of 10 blazars

Automatic optical monitoring of 10 blazars

Long-termRandV-band monitoring of some suitable targets for the link between ICRF and the futureGaiacelestial reference frame

Photocentric variability of quasars caused by variations in their inner structure: consequences forGaiameasurements

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