Universitat de - Departament d'Astronomia i Meteorologia ...

86 Chapter 2. Multiwavelength approach to LS 5039
2.9 Conclusions
1. Most of the known microquasars have been discovered only after undergoing
a noticeable outburst, that has triggered the detection by a battery of satel-
lites and ground-based observatories. In contrast, we have discovered a new
microquasar, namely LS 5039, after careful examination of modern archive
databases and follow-up interferometric radio observations with different res-
olution (with the VLA, VLBA, EVN and MERLIN).
2. We have found that LS 5039 displays persistent radio emission in the form of
relativistic jets, with a high brightness temperature of ∼ 10 8 K and an optically
thin spectral index of α −0.5. These results are indicative of non-thermal
synchrotron radiation mechanism.
3. We have obtained the following jet parameters: β 0.15, θ 80 ◦ , a size up to
∼ 1000 AU with a position angle of 125–150 ◦ and a half opening angle smaller
than 6 ◦ . The asymmetry in flux density and distance to the core between
the approaching and receding jet seems to be persistent along time. Small
differences in the position angle of the jets, observed at different epochs and
with different resolutions, suggest bending and/or precession of the jets.
4. The radio emission is moderately variable but no signatures of variability cor-
related with the orbital period, expected because of the LS 5039 eccentric
orbit, have been found. This is probably because of the lack of sensitivity of
the long-term radio observations available up to now (GBI).
5. We have shown that LS 5039 displays slight variability at optical wavelengths,
and moderate variability at near infrared wavelengths. Based on the new
spectral type classification, O6.5V((f)), and recent calibrations of early type
stars, we have estimated a distance of 2.9 ± 0.3 kpc to LS 5039.
6. We have presented new radial velocity measurements (obtained with the INT)
that confirm the 4.1 d orbital period of this binary system.
7. We have analyzed six and a half years of X-ray monitoring (ASM/RXTE) of
LS 5039, and found no evidences of periodic variability. In particular, we have
not found the orbital period of the system, expected because of variable accre-
tion rate along an eccentric orbit, probably because the source is marginally
detected in the analyzed dataset.