Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and Radio Variability of BL Lacertae   We observed the prototype blazar, BL Lacertae, extensively in optical and
radio bands during an active phase in the period 2010--2013 when the source
showed several prominent outbursts. We searched for possible correlations and
time lags between the optical and radio band flux variations using
multifrequency data to learn about the mechanisms producing variability. During
an active phase of BL Lacertae, we searched for possible correlations and time
lags between multifrequency light curves of several optical and radio bands. We
tried to estimate any possible variability timescales and inter-band lags in
these bands. We performed optical observations in B, V, R and I bands from
seven telescopes in Bulgaria, Georgia, Greece and India and obtained radio data
at 36.8, 22.2, 14.5, 8 and 4.8 GHz frequencies from three telescopes in
Ukraine, Finland and USA. Significant cross-correlations between optical and
radio bands are found in our observations with a delay of cm-fluxes with
respect to optical ones of ~250 days. The optical and radio light curves do not
show any significant timescales of variability. BL Lacertae showed many optical
'mini-flares' on short time-scales. Variations on longer term timescales are
mildly chromatic with superposition of many strong optical outbursts. In radio
bands, the amplitude of variability is frequency dependent. Flux variations at
higher radio frequencies lead the lower frequencies by days or weeks.
  The optical variations are consistent with being dominated by a geometric
scenario where a region of emitting plasma moves along a helical path in a
relativistic jet. The frequency dependence of the variability amplitude
supports an origin of the observed variations intrinsic to the source.

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The categories of this paper are: q-alg
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The categories of this paper are: q-bio
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The categories of this paper are: quant-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: econ