Issue |
A&A
Volume 404, Number 1, June II 2003
|
|
---|---|---|
Page(s) | 133 - 144 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20030435 | |
Published online | 26 May 2003 |
The spectral-curvature parameter: An alternative tool for the analysis of synchrotron spectra
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
3
ASTRON/NFRA, Postbus 2, 7990 AA Dwingeloo, The Netherlands
4
Istituto di Radioastronomia del CNR, via P. Gobetti 101, 40129 Bologna, Italy
Corresponding author: B. W. Sohn, bwsohn@mpifr-bonn.mpg.de
Received:
23
August
2001
Accepted:
17
March
2003
A new intuitive tool for the analysis of synchrotron spectra is presented.
The so–called Spectral Curvature Parameter (SCP), when plotted versus
the high–frequency spectral index () of synchrotron
sources, provides crucial parameters on the continuum spectrum of
synchrotron radiation without the more complex modeling of spectral
ageing scenarios.
An important merit of the SCP-α diagram, in respect to the conventional
colour-colour diagram (i.e. α-α diagram), is the enhanced
reliability of extracting multiple injection spectra,
.
Different from the colour-colour diagram, tracks of different
s,
especially when the synchrotron particles are young, exhibit less overlap and
less smearing in the SCP-α diagram.
Three giant radio galaxies (GRGs) and a sample of Compact steep spectrum
(CSS) souces, which are parti cularly suitable for
this kind of analysis, are presented.
GRGs exhibit asymmetries of their injection spectral indices
in the SCP-
diagram.
The obtained
s and the trends in the sources are
cross-checke with the literature and show remarkable confidence.
Besides the spectral steepening which is well understood in the
framework of synchrotron ageing models, spectral flattening is prominent in
the radio lobes. The spectral flattening is a clue to efficient
re-acceleration processes in the lobes. This implies that interaction with
the surrounding intergalactic or intra-cluster medium is an important
characteristic of GRGs. In the SW lobe of DA 240, there is a clear sign of CI and KP/JP bifurcation at the source extremity. This indicates a highly
relativistic energy transportation from the core or in situ acceleration
in this typical FR I lobe. Our analysis proves, if exists, KP spectra imply
the existence of strong Bsync field with
.
In the CSS sources, our result confirms the CI model and
. The synchrotron self-absorption is significant
in the CSS sample.
Key words: galaxies: jets / radio continuum: galaxies / methods: data analysis
© ESO, 2003
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