<i>BVRI</i> photometry of BL Lacertae in 1993-1995

Maesano, M.; Montagni, F.; Massaro, E.; Nesci, R.

doi:10.1051/aas:1997101

Cited by 26 publications

(20 citation statements)

References 7 publications

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“…The general sense of this variation is that the spectrum becomes bluer when the source is brighter, as already observed by several authors for a few BL Lac objects (e.g. Ghisellini et al 1997;Maesano et al 1997;Massaro et al 1996;Tosti et al 1998;Takalo et al 1996; but see de Diego et al 1997 for an opposite case). ii) The correlation is not equally good for all our objects: only 4 out of our sample of 8 show a correlation r > 0.7, apparently those with an estimated lower value of beaming.…”

Section: Observations and Resultssupporting

confidence: 63%

Spectral Variability of BL Lac Objects

D’Amicis

Nesci

Massaro

et al. 2002

Publ. – Astron. Soc. Aust

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We present the relation between optical luminosity and spectral slope for eight BL Lac objects (3C66A, PKS 0422+00, S5 0716+71, OJ 287, ON 231, OQ 530, S5 1803+78 and BL Lacertae), derived from B, V, R, and I observations spanning a time interval of about 5 years. Four objects show a marked correlation between spectral slope and luminosity, being bluer when brighter, while for the other four the correlation is weaker or absent. Possible explanations are briefly discussed in the framework of current models of the BL Lac phenomenon.

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Section: Observations and Resultssupporting

confidence: 63%

Spectral Variability of BL Lac Objects

D’Amicis

Nesci

Massaro

et al. 2002

Publ. – Astron. Soc. Aust

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“…BVRI photometry of BL Lacertae in 1993-1995 was presented by Maesano et al (1997), confirming the spectral flattening for a flux increase.…”

Section: Bl Lacertaesupporting

confidence: 58%

The WEBT BL Lacertae Campaign 2000

Villata

Raiteri

Kurtanidze

et al. 2002

A&A

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157

131

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Abstract. We present UBVRI light curves of BL Lacertae from May 2000 to January 2001, obtained by 24 telescopes in 11 countries. More than 15 000 observations were performed in that period, which was the extension of the Whole Earth Blazar Telescope (WEBT) campaign originally planned for July-August 2000. The exceptional sampling reached allows one to follow the flux behaviour in fine detail. Two different phases can be distinguished in the light curves: a first, relatively low-brightness phase is followed by an outburst phase, after a more than 1 mag brightening in a few weeks. Both the time duration (about 100 d) and the variation amplitude (roughly 0.9 mag) are similar in the two phases. Rapid flux oscillations are present all the time, involving variations up to a few tenths of mag on hour time scales, and witnessing an intense intraday activity of this source. In particular, a half-mag brightness decrease in about 7 h was detected on August 8-9, 2000, immediately followed by a ∼0.4 mag brightening in 1.7 h. Colour indexes have been derived by coupling the highest precision B and R data taken by the same instrument within 20 min and after subtracting the host galaxy contribution from the fluxes. The 620 indexes obtained show that the optical spectrum is weakly sensitive to the long-term trend, while it strictly follows the short-term flux behaviour, becoming bluer when the brightness increases. Thus, spectral changes are not related to the host galaxy contribution, but they are an intrinsic feature of fast flares. We suggest that the achromatic mechanism causing the long-term flux base-level modulation can be envisaged in a variation of the relativistic Doppler beaming factor, and that this variation is likely due to a change of the viewing angle. Discrete correlation function (DCF) analysis reveals the existence of a characteristic time scale of variability of ∼7 h in the light curve of the core WEBT campaign, while no measurable time delay between variations in the B and R bands is found.

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“…Contamination by background light arising from nearby sources was removed by introducing ad hoc exclusion regions. Adopting the N H value provided by the XRT analysis and assuming E(B − V ) = 0.34 mag (Maesano et al 1997), we estimated R V = 3.2 (Güver &Özel 2009). Then, the optical/UV galactic extinction coefficients were applied (Fitzpatrick 1999).…”

Section: X-ray and Ultravioletmentioning

confidence: 99%

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

Arlen¹,

Aune²,

Beilicke³

et al. 2012

ApJ

100

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We report on the detection of a very rapid TeV gamma-ray flare from BL Lacertae on 2011 June 28 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The flaring activity was observed during a 34.6 minute exposure, when the integral flux above 200 GeV reached (3.4 ± 0.6) × 10 −6 photons m −2 s −1 , roughly 125% of the Crab Nebula flux measured by VERITAS. The light curve indicates that the observations missed the rising phase of the flare but covered a significant portion of the decaying phase. The exponential decay time was determined to be 13 ± 4 minutes, making it one of the most rapid gamma-ray flares seen from a TeV blazar. The gamma-ray spectrum of BL Lacertae during the flare was soft, with a photon index of 3.6 ± 0.4, which is in agreement with the measurement made previously by MAGIC in a lower flaring state. component from the core around the time of the TeV gamma-ray flare, accompanied by changes in the optical polarization angle. Changes in flux also appear to have occurred at optical, UV, and GeV gamma-ray wavelengths at the time of the flare, although they are difficult to quantify precisely due to sparse coverage. A strong flare was seen at radio wavelengths roughly four months later, which might be related to the gamma-ray flaring activities. We discuss the implications of these multiwavelength results.

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BVRI photometry of BL Lacertae in 1993-1995

Cited by 26 publications

References 7 publications

Spectral Variability of BL Lac Objects

Spectral Variability of BL Lac Objects

The WEBT BL Lacertae Campaign 2000

RAPID TeV GAMMA-RAY FLARING OF BL LACERTAE

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