[Paper Review] Modelling the submillimetre-to-radio flaring behaviour of 3C 273

M. Türler, T. J.-L. Courvoisier+1 more|arXiv (Cornell University)|Jun 16, 1999

Astrophysics and Cosmic Phenomena1 references9 citations

TL;DR

This paper models the submillimetre-to-radio flaring behaviour of the quasar 3C 273 by decomposing its long-term light curves into twelve self-similar, model-independent flares. It finds that the optically thin spectral index flattens from -1.1 during the rising phase to -0.5 during the declining phase, supporting synchrotron and/or Compton losses as dominant cooling mechanisms in early shock evolution, with high-frequency peaking flares evolving faster than low-frequency ones.

ABSTRACT

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.

Motivation & Objective

• To understand the spectral and temporal evolution of flaring events in 3C 273's relativistic jet using long-term multiwavelength data.
• To test predictions of shock models in relativistic jets using observed flaring behaviour.
• To determine whether radiative cooling dominates electron energy loss during flare evolution.
• To investigate the relationship between flare timescale and peak frequency in the jet.
• To link identified flares with known VLBI components to validate the decomposition approach.

Proposed method

• The authors decompose the submillimetre-to-radio light curves of 3C 273 into a series of twelve self-similar, model-independent flares.
• They use a parameterization that preserves the shape of each flare across frequencies, enabling consistent spectral and temporal evolution analysis.
• The method allows extraction of spectral index evolution without assuming a specific physical model a priori.
• A second, physical modeling approach is applied to fit three-stage shock models to the decomposed flares.
• The spectral index evolution is tracked from the rising to declining phases of each flare to assess cooling mechanisms.
• The correlation between peak frequency and timescale is analyzed to infer shock formation distance from the jet core.

Experimental results

Research questions

• RQ1 How does the spectral index evolve during the rise and decay of a typical flare in 3C 273’s jet?
• RQ2 Is the observed spectral evolution consistent with the shock model of Marscher & Gear (1985)?
• RQ3 Are radiative losses (synchrotron and/or Compton) the dominant electron cooling mechanism during early flare phases?
• RQ4 Do flares peaking at higher frequencies evolve faster than those peaking at lower frequencies?
• RQ5 Can the identified flares be associated with known VLBI components in the jet?

Key findings

• The optically thin spectral index flattens from -1.1 during the rising phase to -0.5 during the declining phase, consistent with a power-law electron energy distribution index of -2.0.
• This flattening provides strong support for radiative cooling—primarily synchrotron and/or Compton losses—as the dominant electron energy loss mechanism during the initial shock phase.
• High-frequency peaking flares evolve faster than low-frequency peaking flares, suggesting a correlation with shock formation distance from the jet core.
• The decomposed flares align well with the positions and dynamics of known VLBI components in the jet, validating the decomposition method.
• The observed flare evolution is in good qualitative agreement with predictions from the three-stage shock model of Marscher & Gear (1985).
• The model-independent decomposition successfully captures the essential spectral and temporal features of the flares without assuming a specific physical geometry a priori.