Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst
  phase. Detection of the little and big blue bumps   The blazar 3C 454.3 underwent an unprecedented optical outburst in spring
2005. This was first followed by a mm and then by a cm radio outburst, which
peaked in February 2006. We report on follow-up observations by the WEBT to
study the multiwavelength emission in the post-outburst phase. XMM-Newton
observations on July and December 2006 added information on the X-ray and UV
fluxes. The source was in a faint state. The radio flux at the higher
frequencies showed a fast decreasing trend, which represents the tail of the
big radio outburst. It was followed by a quiescent state, common at all radio
frequencies. In contrast, moderate activity characterized the NIR and optical
light curves, with a progressive increase of the variability amplitude with
increasing wavelength. We ascribe this redder-when-brighter behaviour to the
presence of a "little blue bump" due to line emission from the broad line
region, which is clearly visible in the source SED during faint states.
Moreover, the data from the XMM-Newton OM reveal a rise of the SED in the UV,
suggesting the existence of a "big blue bump" due to thermal emission from the
accretion disc. The X-ray spectra are well fitted with a power-law model with
photoelectric absorption, possibly larger than the Galactic one. However, the
comparison with previous X-ray observations would imply that the amount of
absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum
presents a curvature, which may depend on the X-ray brightness. In this case,
two scenarios are possible.

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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: math
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The categories of this paper are: chem-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
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The categories of this paper are: cs
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th