Four Years of Monitoring Blazar PKS 2155−304 with<i>BeppoSAX</i>: Probing the Dynamics of the Jet

Zhang, Y. H.; Treves, A.; Celotti, A.; Chiappetti, L.; Fossati, G.; Ghisellini, G.; Maraschi, L.; Pian, E.; Tagliaferri, G.; Tavecchio, F.

doi:10.1086/340349

Cited by 107 publications

(127 citation statements)

References 55 publications

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“…Similar behaviour was also detected in other sources, such as PKS 2155-304 Zhang et al 2002a) or BL Lacertae (Böttcher et al 2003).…”

Section: Time Resolved Spectral Analysissupporting

confidence: 80%

“…Following the treatment of Zhang et al (2002a), we can express the cooling timescale t cool and the acceleration timescale t acc in the observer frame as a function of the photon energy E (in keV) as:…”

Section: Discussionmentioning

confidence: 99%

“…t acc (E) = 9.65 × 10 −2 (1 + z) 3/2 ξB −3/2 δ −3/2 E 1/2 s ( 3 ) where z is the redshift of the source, B is the magnetic field in Gauss, δ is the Doppler factor of the emitting region and ξ is a parameter indicating the acceleration rate of electrons (see Zhang et al 2002a). As shown by Eqs.…”

Section: Discussionmentioning

confidence: 99%

“…where E s and E h are the mean energies in the corresponding energy bands, taking into account the power-law shape of the spectrum (Zhang et al 2002a). …”

Section: Discussionmentioning

confidence: 99%

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Observing Mkn 421 with XMM-Newton: The EPIC–PN point of view

Ravasio¹,

Tagliaferri²,

Ghisellini³

et al. 2004

A&A

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Abstract. We present three observations (four exposures) of Mkn 421 performed by XMM-Newton in November and December 2002, concentrating on the EPIC-PN camera data. The X-ray spectra were soft and steepened toward high energies. The source was highly variable and the hardness ratio plots displayed a clear harder-when-stronger correlation. During two complete flares the source showed strong spectral evolution: a hardness ratio and a time resolved spectral analysis revealed both clockwise and counterclockwise rotating loop patterns, suggesting the presence of temporal lags between different energy band variations. We confirmed this result and estimated the delay with a cross-correlation analysis performed on the single flares, discussing also variability patterns that could reproduce the asymmetry seen in the cross-correlation function. We verified our findings by reproducing the two flares with analytical models. We obtained consistent results: during one flare, Mkn 421 displayed soft lags, while in the other case it showed hard lags. In both cases, the delay increases with the energy difference between the light curves. Finally, we discuss the presence and the frequency dependence of the temporal lags as an effect of particle acceleration, cooling and escape timescales, showing that our data are consistent with this picture.

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“…Similar behaviour was also detected in other sources, such as PKS 2155-304 Zhang et al 2002a) or BL Lacertae (Böttcher et al 2003).…”

Section: Time Resolved Spectral Analysissupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…where E s and E h are the mean energies in the corresponding energy bands, taking into account the power-law shape of the spectrum (Zhang et al 2002a). …”

Section: Discussionmentioning

confidence: 99%

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Observing Mkn 421 with XMM-Newton: The EPIC–PN point of view

Ravasio¹,

Tagliaferri²,

Ghisellini³

et al. 2004

A&A

Self Cite

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“…Since then it has been the target of a number of X-ray monitoring programmes. These studies indicated a red-noise type of variability at X-ray frequencies with the characteristic variability timescale of the order of days, and only little power corresponding to intraday flux changes (Zhang et al 1999(Zhang et al , 2002Tanihata et al 2001;Kataoka et al 2001). Frequent X-ray flares are typically characterized by symmetric profiles, superimposed short (∼10 ks) smaller-amplitude flickering, and a variety of soft and hard lags changing from epoch to epoch.…”

Section: Introductionmentioning

confidence: 99%

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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Search for hard lags with intra‐night optical observations of BL Lacertae

Zhang

2016

Astron Nachr

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It is generally believed that the high energy end of synchrotron emission, generated by the most energetic tail of relativistic electrons in the jets, account for the X-ray emission of high-energy peaked BL Lac objects (HBLs) and the optical emission of intermediate-energy peaked BL Lac objects (IBLs). It is thus expected that both should show similar variability characteristics. One of the important variability parameters is the inter-band time lag which probes the acceleration and cooling of relativistic particles responsible for the emission. The switches between soft and hard lags have been detected in the intra-day X-ray variability of a few HBLs, which is not the case for the intra-day optical variability of IBLs yet. We present the results of our intra-night optical observations for BL Lacertae, aiming at searching for hard lags of its optical variations, performed with the 80 cm telescope in fourteen nights of 2010 September-November. Intra-night changes of ∼ 0.2 mag were detected in most of nights. The intra-night variability amplitude tends to become larger from red to blue wavelength, and the optical spectrum hardens with increasing brightness. The intra-night variations correlate between different wavebands, but we did not find significant time lags, either soft or hard. Nevertheless, on November 2, the B band variations showed a sign of lagging the R band ones by 317±214 s. The claim of this hard lag is strongly limited by the photometric precision and time resolution. Therefore, the switches between soft and hard lags of IBLs in the optical bands needs further demonstration with more higher quality observations.

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Four Years of Monitoring Blazar PKS 2155−304 withBeppoSAX: Probing the Dynamics of the Jet

Cited by 107 publications

References 55 publications

Observing Mkn 421 with XMM-Newton: The EPIC–PN point of view

Observing Mkn 421 with XMM-Newton: The EPIC–PN point of view

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

Search for hard lags with intra‐night optical observations of BL Lacertae

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