Lisa Zimmermann, Maria Massi
The TeV emitting X-ray binary LS I +61{\deg}303 has two radio periodicities
that correspond to a large periodic outburst with the same period as the orbit,
26.5 days (phase \Phi), and a second periodicity of 1667 days (phase \Theta),
which modulates the orbital phase and amplitude of the large outburst. Analyses
of the radio spectral index revealed in LS I +61{\deg}303 the presence of the
critical transition typical for microquasars from optically thick emission
(related to a steady jet) to an optically thin outburst (related to a transient
jet), and found that it occurs at \Phi_{crit}, which is modulated by \Theta:
\Phi_{crit}=f(\Theta). We examine the possible implications of averaging high
energy data over large \Theta and \Phi intervals in the light of puzzling
published INTEGRAL results, which differ for different averaging of the data.
In microquasars, a simultaneous transition between two X-ray states occurs at
the switch from optically thick radio emission to an optically thin radio
outburst, from the low/hard to the steep power-law state. Assuming that the
same transition occurs in LS I +61{\deg}303 at \Phi_{crit}, we can show
qualitatively the effect of averaging high energy data on \Theta, by analysing
the effects of averaging radio spectral index data across the same \Theta
interval. We then model the two X-ray states, low/hard and steep power-law
state, and show quantitatively how their mixing can affect the results. When
folded over too large a \Theta interval, spectral data from INTEGRAL can yield
a false picture of the emission behaviour of the source along the orbit because
it may be mixing two spectral states. Furthermore, averaging the data along the
orbit may result in a dominant low/hard spectral state, which, for
insufficiently extended sampling, might appear without a cut-off.
View original:
http://arxiv.org/abs/1112.1558
No comments:
Post a Comment