J/MNRAS/480/5517 Multiwavelength cross-correlations in blazars (Liodakis+, 2018)
Multiwavelength cross-correlations and flaring activity in bright blazars.
Liodakis I., Romani R.W., Filippenko A.V., Kiehlmann S., Max-Moerbeck W.,
Readhead A.C.S., Zheng W.
<Mon. Not. R. Astron. Soc., 480, 5517-5528 (2018)>
=2018MNRAS.480.5517L 2018MNRAS.480.5517L (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Gamma rays
Keywords: relativistic processes - galaxies: active - galaxies: jets
Abstract:
Blazars are known for their energetic multiwavelength flares from
radio wavelengths to high-energy γ-rays. In this work, we study
radio, optical, and γ-ray light curves of 145 bright blazars
spanning up to 8 yr, to probe the flaring activity and interband
correlations. Of these, 105 show >1σ correlations between one or
more wavebands, 26 of which have a >3σ correlation in at least
one wavelength pair, as measured by the discrete correlation function.
The most common and strongest correlations are found between the
optical and γ-ray bands, with fluctuations simultaneous within
our ∼30d resolution. The radio response is usually substantially
delayed with respect to the other wavelengths with median time lags of
∼100-160d. A systematic flare identification via Bayesian block
analysis provides us with a first uniform sample of flares in the
three bands, allowing us to characterize the relative rates of
multiband and 'orphan' flares. Multiband flares tend to have higher
amplitudes than 'orphan' flares.
Description:
We use data from the Owens Valley Radio Observatory (OVRO; 15GHz) 40-m
telescope (Richards et al. 2011ApJS..194...29R 2011ApJS..194...29R, Cat. J/ApJS/194/29),
the 0.76-m optical Katzman Automatic Imaging Telescope (KAIT;
unfiltered charge-coupled device exposures roughly corresponding to
the R band) at Lick Observatory (Filippenko et al.
2001ASPC..246..121F 2001ASPC..246..121F; Li et al. 2003PASP..115..844L 2003PASP..115..844L), and the monthly
averaged Large Area Telescope (LAT) γ-ray light curves from
Fermi3 (Acero et al. 2015ApJS..218...23A 2015ApJS..218...23A, Cat. J/ApJS/218/23). The
γ-ray light curves are automatically generated through aperture
photometry using PASS8 and the latest FTOOLS package. The photometry
is in the 0.1-200GeV range with a 1 deg radius aperture on a monthly
cadence, though observations <5deg from the Sun have been excluded.
OVRO and KAIT have been monitoring blazars since 2007 and 2009,
respectively, in support of Fermi. Both programs run in a fully
automated mode with an approximate cadence of 3d. The full description
of the reduction pipelines for both KAIT and OVRO can be found in Li
et al. (2003PASP..115..844L 2003PASP..115..844L) and Richards et al. (2011ApJS..194...29R 2011ApJS..194...29R,
Cat. J/ApJS/194/29), respectively. The sources in our sample common to
these programs are all relatively bright objects from the first LAT
blazar catalogue (Abdo et al. 2010ApJ...715..429A 2010ApJ...715..429A, Cat.
J/ApJ/715/429). The optical and γ-ray light curves are publicly
available online, while the radio light curves are publicly available
through the OVRO team. In this work we are considering observations
from 2008 January until 2017 May for the radio, 2009 July until 2017
November for the optical, and 2008 August until 2017 November for the
γ-rays.
Our final sample consists of the 145 common sources between OVRO,
KAIT, and Fermi, 93 of which are BL Lacs, 47 are FSRQs, and 5 are as
yet unclassified sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 73 145 Cross-correlation results for the sources in
our sample that showed a >1σ significant
DCF peak
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name KAIT name (JHHMM+DDMM)
12 A1 --- Class [BF-] Class (B for BL Lacs, F for FSRQs)
14- 18 F5.3 --- z ? Redshift
20- 25 F6.2 --- tauor ? Optical-radio time lag (1)
27- 31 F5.2 --- e_tauor ? Error on tauor
33- 36 F4.2 --- SigniDCFor ? Significance of the peak DCFo-r
coefficient (2)
38- 43 F6.2 --- tauog ? Optical-γ-rays time lag (1)
45- 49 F5.2 --- e_tauog ? Error on tauog
51- 54 F4.2 --- SigniDCFog ? Significance of the peak DCFo-g
coefficient (2)
56- 62 F7.2 --- taugr ? γ-ray-radio time lag (1)
64- 68 F5.2 --- e_taugr ? Error on taugr
70- 73 F4.2 --- SigniDCFgr ? Significance of the peak DCFg-r
coefficient (2)
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Note (1): Once a DCF peak was identified, we fitted it with a Gaussian function
to best determine the cross-correlation coefficient at the peak as
well as the peak-weighted time lag (τ) and its uncertainty.
For a positive tauor or tauog, the optical emission is leading the
radio or γ-rays, respectively.
For a positive taugr the γ-ray emission is leading the radio.
Note (2): To probe the strong intraband correlations quantitatively, we
calculate the discrete correlation function (DCF;
Edelson & Krolik 1988ApJ...333..646E 1988ApJ...333..646E) for each pair of wavebands.
For two time series with observations the DCF is defined through the
unbinned discrete correlation UCDFij as DCFτ=UCDFij/N.
σDCF(τ) is the standard error of the DCF.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 02-Jun-2022