Tuorla quasar monitoring

Katajainen, S.; Takalo, L. O.; Sillanpää, A.; Nilsson, K.; Pursimo, T.; Hanski, M.; Heinämäki, P.; Kotoneva, Eira; Lainela, M.; Nurmi, P.; Pietilä, H.; Rekola, R.; Riehokainen, A.; Teerikorpi, P.; Valtaoja, E.; Lähteenmäki, A.

doi:10.1051/aas:2000184

Cited by 59 publications

(63 citation statements)

References 52 publications

(95 reference statements)

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“…However, occasional sharp flares have also been observed in CTA 102. Variations as high as ∆B = 1. m 07 in 2 days [4] and ∆V = 1. m 13 in 3 days [6] were observed in 1978 and 1996, correspondingly. The previously reported historical maximum for the object, R ≈ 14. m 5, was reached on Oct. 4, 2004 during a short-term event accompanied by prominent intranight variability [7].…”

Section: Introductionmentioning

confidence: 84%

Prominent outburst of the blazar CTA 102 in 2012

Larionov

Blinov

Jorstad

et al. 2013

EPJ Web of Conferences

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Abstract. After a few years of quiescence, the blazar CTA 102 underwent a large outburst in the fall of 2012. The flare has been tracked from γ-rays to near-infrared, including Fermi and Swift data as well as polarimetric data from several observatories. An intensive GASP-WEBT collaboration campaign in optical and NIR bands, with the addition of previously unpublished archival data, allows comparison of this outburst with the previous activity period of this blazar in the early 2000s. We find remarkable similarity between the optical and γ-ray behavior of CTA 102 during the outburst, without any time lag between the two light curves, indicating co-spatiality of the optical and γ-ray emission regions. A strong harder-when-brighter spectral dependence is seen both in γ-rays and optical. The polarimetric behavior of CTA 102 during the outburst conforms with a shock-in-jet interpretation.

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Section: Introductionmentioning

confidence: 84%

Prominent outburst of the blazar CTA 102 in 2012

Larionov

Blinov

Jorstad

et al. 2013

EPJ Web of Conferences

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“…Some periods obtained in this study, for the well-observed BL Lacertae object B0716+714, are already known. A period of 68 days is mentioned by Katajainen et al (2000), and a period of three years is mentioned by Raiteri et al (2003). For the BL Lac object B1215+303, two periods of 4.45 and 6.89 yr are mentioned by Fan et al (2002).…”

Section: Periodogram Analysis Of the Observational Datamentioning

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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“…Webb et al (1998), Bai et al (1999), Tosti et al (1999), Ghosh et al (2000), Katajainen et al (2000), Clements & Carini (2001), Fan et al (2001), Sobrito et al (2001), Papadakis et al (2003), Tosti et al (2004).…”

Section: Observations Of Bl Lacertae By the Webt Collaborationmentioning

confidence: 99%

The WEBT BL Lacertae Campaign 2001 and its extension

Villata

Raiteri

Kurtanidze

et al. 2004

A&A

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123

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paper we present UBVRI light curves obtained by the WEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ∼15 600 observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a fewday time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ∼0.1 bluerwhen-brighter slope in the B − R versus R plane; a steeper slope of ∼0.4 would distinguish the shorter-term variations. This means that, when considering the long-term trend, the B-band flux level is related to the R-band one according to a power law of index ∼1.1. Doppler factor variations on a "convex" spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism.

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Tuorla quasar monitoring

Cited by 59 publications

References 52 publications

Prominent outburst of the blazar CTA 102 in 2012

Prominent outburst of the blazar CTA 102 in 2012

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

The WEBT BL Lacertae Campaign 2001 and its extension

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