arXiv subjects

T. J. -L. Courvoisier

Publications and source records attributed to T. J. -L. Courvoisier.

76 records · Page 5Linked to original sources

arXiv1999

Modelling the submillimetre-to-radio flaring behaviour of 3C 273

We present a new approach to derive the observed properties of synchrotron outbursts in relativistic jets. The idea is to use the very well sampled submillimetre-to-radio long-term light curves of 3C 273 to extract the spectral and temporal evolution of a typical outburst. The method consists in a decomposition of these light curves into a series of twelve self-similar flares. With a model-independent parameterization, we find that the obtained outburst's evolution is in good qualitative agreement with the expectations of shock models in relativistic jets. We then derive, by a second approach, the relevant parameters of three-stage shock models. We observe for the first time that the optically thin spectral index is steeper during the initial rising phase of the evolution than during the final declining phase as expected by the shock model of Marscher & Gear (1985). We obtain that this index flattens from alpha=-1.1 to alpha=-0.5, in good agreement with what is expected from a power law electron energy distribution with an index of -2.0. The observed flattening gives support to the idea that radiative (synchrotron and/or Compton) losses are the dominant cooling process of the electrons during the initial phase of the shock evolution. Two other results give us confidence in our decomposition: 1) the outbursts that we identify do well correspond to the VLBI components observed in the jet and 2) there is strong evidence that high-frequency peaking outbursts evolve faster than low-frequency peaking outbursts. We propose that this last correlation is related to the distance from the core of the jet at which the shock forms.

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arXiv1998

30 years of multi-wavelength observations of 3C 273

We present a wide multi-wavelength database of most observations of the quasar 3C 273 obtained during the last 30 years. This database is the most complete set of observations available for an active galactic nucleus (AGN). It contains nearly 20'000 observations grouped together into 70 light curves covering 16 orders of magnitude in frequency from the radio to the gamma-ray domain. The database is constituted of many previously unpublished observations and of most publicly available data gathered in the literature and on the World Wide Web (WWW). It is complete to the best of our knowledge, except in the optical (UBV) domain where we chose not to add all observations from the literature. In addition to the photometric data, we present the spectra of 3C 273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the X-ray domain, we used the spectral fit parameters from the literature to construct the light curves. Apart from describing the data, we show the most representative light curves and the average spectrum of 3C 273. The database is available on the WWW in a homogeneous and clear form and we wish to update it regularly by adding new observations.

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arXiv1997

Relationship between X-ray and ultraviolet emission in 3C 273

In 3C 273, ultraviolet flux and X-ray flux measured by BATSE are not well correlated, contrarily to predictions of several models, unless the X-ray flux lags the UV emission by 1.75 yr. The absence of observed correlation at small lag cannot be due to spectral variability. A Comptonizing corona model is however compatible with all UV and X-ray observations covering the BATSE period.

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arXiv1997

Very rapid optical variability of PKS 2155-304

We have performed an optical observation campaign on PKS 2155-304, whose aim was to determine the variability properties of this object on very short time scales in several photometric bands. We detected variability on time scales as short as 15 min. The Fourier properties of the light curves have been investigated using structure function analysis. The power spectra are well described by a power-law with an index -2.4. It is compatible with the index found in the X-ray domain. The value of this index shows that the light curves cannot be generated by a sum of exponential pulses. Using historical data, we find that the longest time scale of variability in the optical domain lies between 10 and 40 days. We find a strong correlation between flux and spectral index, which we interpret as the signature of an underlying constant component. As a result we do not find evidence of spectral variation for the active nucleus in the optical domain. A lag has been found between the light curves in different optical bands. The short-wavelength light curves lead the long-wavelength ones. The amplitude of the lag is about 40 min for a factor 2 in wavelength. Our results are compared with predictions from different models. None of them can explain naturally the set of results obtained with this campaign, but we bring out some clues for the origin of the variability.

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