Optical observations of BL Lacertae in 2004–2005

Zhang, Youhong; Bian, Fuyan; Li, Jun-Zheng; Shang, R. C.

doi:10.1093/mnras/stt534

Cited by 7 publications

(12 citation statements)

References 51 publications

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“…This indicates that the relation can be taken as bluer-when-bright trend which appears less, moderately and strongly pronounced during Night 2, Night 3 and Night 4, respectively. Similar observations were made by [46] in their study of the source on intranight timescales. …”

Section: Multi-band Micro-variabilitysupporting

confidence: 85%

Microvariability in BL Lacertae: “Zooming” into the Innermost Blazar Regions

Bhatta

Webb

2018

Galaxies

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In this work, we present the results of our multi-band microvariability study of the famous blazar BL Lac. We performed microvariablity observations of the source in the optical VRI bands for four nights in 2016. We studied the intranight flux and spectral variability of the source in detail with an objective to characterize microvariability in the blazars, a frequently observed phenomenon in blazars. The results show that the source often displays a fast flux variability with an amplitude as large as ~0.2 magnitude within a few hours, and that the color variability in the similar time scales can be characterized as “bluer-when-brighter” trend. We also observed markedly curved optical spectrum during one of the nights. Furthermore, the correlation between multi-band emission shows that in general the emission in all the bands are highly correlated; and in one of the nights V band emission was found to lead the I band emission by ~13 min. The search for characteristic timescale using z-transformed auto-correlation function and the structure function analyses reveals characteristic timescale of ~50 min in one of the R band observations. We try to explain the observed results in the context of the passage of shock waves through the relativistic outflows in blazars.

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Section: Multi-band Micro-variabilitysupporting

confidence: 85%

Microvariability in BL Lacertae: “Zooming” into the Innermost Blazar Regions

Bhatta

Webb

2018

Galaxies

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“…The similarities imply a common origin of the variations, plausibly the most energetic tails of the synchrotron emission produced by the relativistic electrons in the jets, for both the optical emission of low-frequency-peaked BLLs and the X-ray emission of high-frequency-peaked BLLs (Zhang et al, 2013b).…”

Section: Flux Variabilitymentioning

confidence: 83%

An optical view of BL Lacertae objects

Falomo

Pian²,

Treves

2014

Astron Astrophys Rev

140

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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“…Both soft and hard lags were detected in the X-ray variations of HBLs (e.g., Brinkmann et al 2005;Tanihata et al 2001;Ravasio et al 2004;Zhang et al 2002Zhang et al , 2006. For the intra-night optical variations of IBLs, however, hard lags have not been detected yet despite soft lags have been already claimed (e.g., Papadakis et al 2003;Wu et al 2012;Zhang et al 2013).…”

Section: Introductionmentioning

confidence: 97%

“…Cheng, Zhang & Xu (2013) and Zhang et al (2013) have shown that the intra-night optical variations of IBLs are remarkably similar to the X-ray variations of high-energy peaked BL Lac objects (HBLs) on similar timescales (see Pian 2002 andZhang 2003 for reviews). A rational interpretation of such an analogue is that the X-ray emission of HBLs is the high energy tail of synchrotron radiation component of their SEDs as well, even though the synchrotron emission of IBLs and HBLs peaks at different energy.…”

Section: Introductionmentioning

confidence: 99%

“…BL Lac has been monitored in the optical range on various timescales for more than one century (e.g., Fan et al 1998;Villata et al 2002). One of the most prominent outcomes is the dense observations and detailed studies of intra-night (nickname for timescales of hours in case of optical observations) optical variations, such as wavelength-dependent variability amplitude, spectral evolution, and inter-band time lags (e.g., Papadakis et al 2003;Stalin et al 2006;Zhang et al 2013).…”

Section: Introductionmentioning

confidence: 99%

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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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Optical observations of BL Lacertae in 2004–2005

Cited by 7 publications

References 51 publications

Microvariability in BL Lacertae: “Zooming” into the Innermost Blazar Regions

Microvariability in BL Lacertae: “Zooming” into the Innermost Blazar Regions

An optical view of BL Lacertae objects

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

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