The continuum spectral features of blazars in the optical region

Fiorucci, M.; Ciprini, S.; Tosti, G.

doi:10.1051/0004-6361:20034218

Cited by 78 publications

(98 citation statements)

References 45 publications

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“…We found that the spectral index α of PKS 0735+178 varies between 2.11 ± 0.26 to 0.66 ± 0.20, with an average value of 1.25 ± 0.15 in the last ten years. These values for α are roughly in agreement with the values calculated previously in Fiorucci, Ciprini, & Tosti (2004) using only the Perugia Observatory data set.…”

Section: Optical Spectral Indexessupporting

confidence: 91%

Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behavior, and variability timescales

Ciprini

Takalo

Tosti

et al. 2007

A&A

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Aims. New data and results on the optical behaviour of the prominent blazar PKS 0735+178 (also know as OI 158, S3 0735+17, DA 237, 1ES 0735+178, 3EG J0737+1721) are presented, through the most continuous BV RI data available in the period 1994-2004 (about 500 nights of observations). In addition, the whole historical light curve, and a new photometric calibration of comparison stars in the field of this source are reported. Methods. Several methods for timeseries analysis of sparse data sets are developed, adapted and applied to the reconstructed historical light curve and to each observing season of our unpublished optical database on PKS 0735+178. Optical spectral indexes are calculated from the multi-band observations and studied on long-term (years) durations as well. For the first time in this source, variability modes, characteristic timescales and the signal power spectrum are explored and identified over 3 decades in time with a sufficient statistics. The novel investigation of mid-term optical scales (days, weeks), could be also applied and compared to blazar gamma-ray light curves that will be provided, on the same timescales, by the forthcoming GLAST observatory. Results. In the last 10 years the optical emission of PKS 0735+178 exhibited a rather achromatic behaviour and a variability mode resembling the shot-noise. The source was in a intermediate or low brightness level, showing a mild flaring activity and a superimposition/succession of rapid and slower flares, without extraordinary and isolated outbursts but, at any rate, characterized by one major active phase in 2001. Several mid-term scales of variability were found, the more common falling into duration intervals of about 27-28 days, 50-56 days and 76-79 days. Rapid variability in the historical light curve appears to be modulated by a general, slower and rather oscillating temporal trend, where typical amplitudes of about 4.5, 8.5 and 11-13 years can be identified. This spectral and temporal analysis, accompanying our data publication, suggests the occurrence of distinctive signatures at mid-term durations that can likely be of transitory nature. On the other hand the possible pseudo-cyclical or multi-component modulations at long times could be more stable, recurrent and correlated to the bimodal radio flux behaviour and the twisted radio structure observed by several years in this blazar.

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Section: Optical Spectral Indexessupporting

confidence: 91%

Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behavior, and variability timescales

Ciprini

Takalo

Tosti

et al. 2007

A&A

Self Cite

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“…The SEDs of HBL sources peak as a rule above a few keV, and their X-ray energy indices are close to or smaller than unity. Their variability in this band is high in contrast with the optical and radio data, where their flux is more stable (Fiorucci et al 2004). …”

Section: Introductionmentioning

confidence: 79%

Multifrequency observations of a sample of very low frequency peaked BL Lacertae objects

Maselli

Massaro

Nesci

et al. 2010

A&A

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Context. BL Lacertae objects with an extremely low value of the peak frequency (ν s ≤ 10 13 Hz) of the synchrotron component (VLBL objects) are poorly known. Aims. We selected a small sample of these candidate objects on the basis of their radio/optical flux ratio to evaluate their variability, define the low energy part of their SED and obtain a reliable estimate of their ν s through a fit with a log-parabolic law. Methods. They were the object of a ground-based observational campaign in the infrared and optical bands; data from several pointings by the Swift satellite in the UV and X-ray band were also obtained for half the sample. We complemented our data with a large number of literature data. Results. These sources showed a marked flux variability, as expected for BL Lacertae objects of the low energy peaked BL Lac objects (LBL) and intermediate BL Lac objects type; all of them have a ν s value around 10 13 Hz, but this is low enough only for a few sources to consider them genuine VLBL objects. We report the overall properties of individual sources and discuss some aspects of this class of rare objects, which could correspond to the transition between flat spectrum radio quasars and LBLs.

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“…Sitko & Junkkarinen 1985;Stickel et al 1989;Nilsson et al 2010). F ν of OJ 287 exhibits a power-law profile F ν ∼ ν −α in the optical region, with dereddened average α = 1.59 ± 0.22 (Fiorucci 2004). The spectrum of OJ 287 is also variable in the optical region.…”

Section: Determining the Color Correction For Oj287mentioning

confidence: 90%

“…Takalo & Sillanpää 1989;Fiorucci et al 2004). Takalo & Sillanpää (1989) claimed that B − V was higher when OJ 287 was fainter during the years after 1971.…”

Section: Determining the Color Correction For Oj287mentioning

confidence: 99%