Long-term optical variability of PKS 2155-304

Kastendieck, M. A.; Ashley, M. C. B.; Horns, D.

doi:10.1051/0004-6361/201015918

Cited by 36 publications

(41 citation statements)

References 36 publications

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“…This general picture is confirmed by the long-term monitoring of PKS 2155−304 at different frequencies revealing that the typical state of the source corresponds to the lower-activity epochs with the characteristic variability timescales of the order of a few/several days in X-rays (e.g. Kataoka et al 2001), and months in optical (Kastendieck et al 2011). This is exactly the state probed by the observations presented and analysed in this paper.…”

Section: Broadband Sedssupporting

confidence: 84%

“…These campaigns established the intraday variability nature of the source with the shortest flux doubling timescales of about 15 min, detected, however, in only a few isolated epochs (Paltani et al 1997;Heidt et al 1997). The red-noise type of optical variability, comparable to that observed at X-ray frequencies, persists up to variability timescales of about 3 years (Kastendieck et al 2011). In several epochs a clear bluer-whenbrighter evolution of the source has been found (Paltani et al 1997), a behaviour that appears to beuniversal in BL Lac objects (see e.g.…”

Section: Introductionmentioning

confidence: 61%

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Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S.: investigation of optical/γ-ray correlations in different spectral states

Abramowski¹,

Aharonian²,

Benkhali³

et al. 2014

A&A

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In this paper we report on the analysis of all the available optical and very high-energy γ-ray (>200 GeV) data for the BL Lac object PKS 2155−304, collected simultaneously with the ATOM and H.E.S.S. telescopes from 2007 until 2009. This study also includes X-ray (RXTE, Swift) and highenergy γ-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states, and was characterized by only moderate flux changes at different wavelengths on the timescales of days and months. A flattening of the optical continuum with an increasing optical flux can be noted in the collected dataset, but only occasionally and only at higher flux levels. We did not find any universal relation between the very high-energy γ-ray and optical flux changes on the timescales from days and weeks up to several years. On the other hand, we noted that at higher flux levels the source can follow two distinct tracks in the optical flux-colour diagrams, which seem to be related to distinct γ-ray states of the blazar. The obtained results therefore indicate a complex scaling between the optical and γ-ray emission of PKS 2155−304, with different correlation patterns holding at different epochs, and a γ-ray flux depending on the combination of an optical flux and colour rather than a flux alone.

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Section: Broadband Sedssupporting

confidence: 84%

Section: Introductionmentioning

confidence: 61%

Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S.: investigation of optical/γ-ray correlations in different spectral states

Abramowski¹,

Aharonian²,

Benkhali³

et al. 2014

A&A

Self Cite

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“…Although the Lomb-Scargle periodogram (LSP) is not the best way to determine the PSD for red-noise data (Kastendieck et al 2011), it is a good way to find periodicities when dealing with unevenly sampled light curves.…”

Section: Lomb-scargle Periodogrammentioning

confidence: 99%

The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies

Aleksić¹,

Ansoldi²,

Antonelli³

et al. 2015

A&A

104

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Aims. We perform an extensive characterization of the broadband emission of Mrk 421, as well as its temporal evolution, during the non-flaring (low) state. The high brightness and nearby location (z = 0.031) of Mrk 421 make it an excellent laboratory to study blazar emission. The goal is to learn about the physical processes responsible for the typical emission of Mrk 421, which might also be extended to other blazars that are located farther away and hence are more difficult to study. Methods. We performed a 4.5-month multi-instrument campaign on Mrk 421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. This extensive radio to very-high-energy (VHE; E > 100 GeV) γ-ray dataset provides excellent temporal and energy coverage, which allows detailed studies of the evolution of the broadband spectral energy distribution. Results. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign.Appendix A is available in electronic form at http://www.aanda.org The complete data set shown in Fig. 1 Article published by EDP Sciences A126, page 1 of 18 A&A 576, A126 (2015) Conclusions. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multiwavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk 421 during nonflaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies.

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“…Gamma-Ray Bursts), has greatly benefitted the BLL field. These small telescopes (e.g., REM, ROTSE, SMARTS) have flexible schedules and pointing constraints, therefore they can be devoted to long looks of variable sources like BLLs (Tosti et al, 1996;Ciprini et al, 2003;Carini et al, 2004;Gu et al, 2006;Dolcini et al, 2007;Kastendieck et al, 2011;Ackermann et al, 2012;Bonning et al, 2012;Nesci et al, 2013;Sandrinelli et al, 2014).…”

Section: Flux Variabilitymentioning

confidence: 99%

An optical view of BL Lacertae objects

Falomo

Pian²,

Treves

2014

Astron Astrophys Rev

137

109

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BL Lac objects are active nuclei, hosted in massive elliptical galaxies, the emission of which is dominated by a relativistic jet closely aligned with the line of sight. This implies the existence of a parent population of sources with a misaligned jet, that have been identified with low-power radiogalaxies. The spectrum of BL Lacs, dominated by non-thermal emission over the whole electromagnetic range, together with bright compact radio cores, high luminosities, rapid and large amplitude flux variability at all frequencies and strong polarization make these sources an optimal laboratory for high energy astrophysics. A most distinctive characteristic of the class is the weakness or absence of spectral lines, that historically hindered the identification of their nature and ever thereafter proved to be a hurdle in the determination of their distance. In this paper we review the main observational facts that contribute to the present basic interpretation of this class of active galaxies. We overview the history of the BL Lac objects research field and their population as it emerged from multi-wavelength surveys. The properties of the flux variability and polarization, compared with those at radio, X-ray and gamma-ray frequencies, are summarized together with the present knowledge of the host galaxies, their environments, and central black hole masses. We focus this review on the optical observations, that played a crucial role in the early phase of BL Lacs studies, and, in spite of extensive radio, X-ray, and recently gamma-ray observations, could represent the future major contribution to the unveiling of the origin of these sources. In particular they could provide a firm conclusion on the long debated issue of the cosmic evolution of this class of active galactic nuclei and on the connection between formation of supermassive black holes and relativistic jets.

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Long-term optical variability of PKS 2155-304

Cited by 36 publications

References 36 publications

Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S.: investigation of optical/γ-ray correlations in different spectral states

Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S.: investigation of optical/γ-ray correlations in different spectral states

The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies

An optical view of BL Lacertae objects

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