Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2011-05-21
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
12 pages, MNRAS, in press
Scientific paper
We study free-free absorption of radio emission by winds of massive stars. We derive formulae for the optical depth through the wind measured from a point of emission along a jet, taking into account Compton and photoionization heating and Compton, recombination, line and advection cooling. We apply the developed formalism to radio monitoring data for Cyg X-1, which allows us to obtain strong constraints on the structure of its inner jet. With the data at 15 GHz, and taking into account an anisotropy of the stellar wind in Cyg X-1, we estimate the location of the peak of that emission along the jet at about one orbital separation, i.e., $\sim 3\times 10^{12}$ cm. Given a previous determination of the turnover frequency in Cyg X-1, this implies the location of the base of the jet at $\sim 10^3$ gravitational radii. We also obtain corresponding results at 8.3 GHz and 2.25 GHz, which roughly follow the standard conical partially self-absorbed jet model. Furthermore, we find that the level of the orbital modulation depends on the radio flux, with the modulation being substantially stronger when the radio flux is lower. This is explained by the height of the radio emission along the jet decreasing with the decreasing radio flux, as predicted by jet models. Based on the finding of the flux-dependent orbital modulation, we are able to estimate a range of the possible changes of the form of the radio/X-ray correlation in Cyg X-1 due to free-free absorption. We also derive predictions for the orbital modulation and flux attenuation at frequencies beyond the 2.25--15 GHz range.
No associations
LandOfFree
The structure of the jet in Cyg X-1 inferred from orbital modulation of the radio emission does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The structure of the jet in Cyg X-1 inferred from orbital modulation of the radio emission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The structure of the jet in Cyg X-1 inferred from orbital modulation of the radio emission will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-329856