Fast variability of BL Lacertae at 1 μm

Massaro, E.; Nesci, R.; Maesano, M.; Montagni, F.; D’Alessio, F.

doi:10.1046/j.1365-8711.1998.01696.x

Cited by 45 publications

(50 citation statements)

References 3 publications

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“…As can be seen from the Table 3 the amplitude of variability is larger in V band LCs than the R passband LCs. The amplitude of variations is mostly found to increase with frequency thus implying that the source spectrum becomes flatter when brightness of source increases (Massaro et al 1998) which is also the case with our target.…”

Section: Flux and Colour Variability Resultssupporting

confidence: 77%

Multiband optical variability studies of BL Lacertae

Agarwal¹,

Gupta²

2015

Monthly Notices of the Royal Astronomical Society

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We monitored BL Lacertae for 13 nights in optical B, V, R, and I bands during October and November 2014 including quasi-simultaneous observations in V and R bands using two optical telescopes in India. We have studied multi-band optical flux variations, colour variation and spectral changes in this blazar. Source was found to be active during the whole monitoring period and showed significant intraday variability on 3 nights in V and R filters while displayed hints of variability on 6 other dates in R passband and on 2 nights in V filter. From the colour-magnitude analysis of the source we found that the spectra of the target gets flatter as it becomes brighter on intra-night timescale. Using discrete correlation technique, we found that intraday light curves in both V and R filters are almost consistent and well correlated with each other. We also generated spectral energy distribution (SED) of the target using the B, V, R, and I data sets for all 13 nights which could help us investigate the physical process responsible for the observed variations in BL Lacertae objects. We also discuss possible physical causes of the observed spectral variability.

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Section: Flux and Colour Variability Resultssupporting

confidence: 77%

Multiband optical variability studies of BL Lacertae

Agarwal¹,

Gupta²

2015

Monthly Notices of the Royal Astronomical Society

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“…An extremely fast brightening of 0.6 mag in 40 min was detected by Matsumoto et al (1999) on August 2, 1997, inside a larger flux increase of more than 1 mag between 17 and 19 UT, confirmed by Ghosh et al (2000). In the same night, the decreasing phase of the flare was observed by Massaro et al (1998) and Speziali & Natali (1998) as a variation of more than half a mag in about 2 h (see also Ghosh et al 2000). Rapid and large-amplitude flux variations were also observed by Sobrito et al (1999) and Tosti et al (1999).…”

Section: Bl Lacertaementioning

confidence: 66%

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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“…In general, the variations in blazars are dominated by the jet emission. There have been extensive studies of the optical variability of blazars (e.g., Ghisellini et al 1997;Fan et al 1998;Massaro et al 1998;Ghosh et al 2000;Clements & Carini 2001;Raiteri et al 2001;Villata et al 2002;Vagnetti et al 2003;Wu et al 2005Wu et al , 2007Gu et al 2006;Hu et al 2006;Poon et al 2009;Rani et al 2010;Gu & Ai 2011). While it is generally accepted that the nonthermal emission from relativistic jet oriented close to the line of sight dominates the optical continuum, the situation seems more complicated in FSRQs.…”

Section: Introductionmentioning

confidence: 99%

“…The optical variations of SSRQs have been poorly studied, and few explanations have been presented (e.g., Stalin et al 2004Stalin et al , 2005. While the color variations and/or spectral variations of blazars have been extensively investigated (e.g., Ghisellini et al 1997;Fan et al 1998;Massaro et al 1998;Ghosh et al 2000;Clements & Carini 2001;Raiteri et al 2001;Villata et al 2002;Vagnetti et al 2003;Wu et al 2005Wu et al , 2007Gu et al 2006;Rani et al 2010;Gu & Ai 2011), it has not been the case for SSRQs. In this work, we investigate the optical variability of a sample of SSRQs, as well as their spectral variations.…”

Section: Introductionmentioning

confidence: 99%

The optical variability of steep-spectrum radio quasars in the SDSS stripe 82 region

Gu¹,

2011

A&A

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Context. There have been many investigations of the optical variability of flat-spectrum radio quasars (FSRQs), but the optical variability of steep-spectrum radio quasars (SSRQs) has been poorly studied. Aims. We investigate the optical variability of SSRQs, comparing this with the optical variability of FSRQs. Methods. We measure the optical variability of 18 SSRQs and 15 FSRQs in the SDSS Stripe 82 region using SDSS DR7 released multi-epoch data covering about nine years. We determine the spectral index by fitting a power law to SDSS ugriz photometric data, and explore the relationship between this spectral index and source brightness. Results. For all SSRQs studied, we detect variations in r band flux of overall amplitude between 0.22 mag and 0.92 mag in different sources. Eight of 18 SSRQs display a bluer-when-brighter (BWB) trend. In contrast, the variability amplitude of 15 FSRQs in r band ranges from 0.18 to 0.97 mag, and 11 of 15 sources follow a BWB trend. For all SSRQs studied, we found an anti-correlation between the Eddington ratio and the variability amplitude in r band, which is similar to that in radio-quiet AGNs. This implies that the thermal emission from the accretion disk may be responsible for the variability in SSRQs, although the jet nonthermal emission cannot be excluded. In contrast, there is no correlation found for FSRQs, which implies that the mechanisms of variability in FSRQs may be different from that in SSRQs. The optical continuum variability of radio-loud broad absorption-line quasars (BALQs) are investigated for the first time here for two sources with steep radio spectra. Both radio-loud BALQs display variations with amplitudes of about 0.3 mag at r band. Their spectral variability all follow a BWB trend. In our previous analysis of a combined sample of 18 SSRQs and 44 FSRQs, we found that the line width of the broad Mg II emission line is broader for steeper radio spectral indices. It implies a disk-like broad line region (BLR) geometry may present in these quasars. In these 62 quasars, we found a ∼57% source percentage showing BWB trend in FSRQs, whereas it is ∼44% in SSRQs.

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Fast variability of BL Lacertae at 1 μm

Cited by 45 publications

References 3 publications

Multiband optical variability studies of BL Lacertae

Multiband optical variability studies of BL Lacertae

The WEBT BL Lacertae Campaign 2000

The optical variability of steep-spectrum radio quasars in the SDSS stripe 82 region

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