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50 Chapter 2. Multiwavelength approach to LS 5039
2.4.5 EVN and MERLIN observations,
confirmation of persistent relativistic radio jets
The persistent radio emission of LS 5039 suggests that the jet is always present.
With the aim to confirm this hypothesis, and also to detect the jet at larger angular
scales than those imaged with the previous Very Long Baseline Array (VLBA) mea-
surements, we observed this microquasar with the European VLBI Network (EVN)
and the Multi-Element Radio-Linked Interferometer Network (MERLIN).
Observations and results
We observed 13 LS 5039 simultaneously with the EVN 14 and MERLIN 15 on 2000
March 1 (3:20–7:10 UT, MJD 51604.2) at 5 GHz. Single dish flux density measure-
ments were carried out with the MPIfR 100 m antenna in Effelsberg. We scheduled
the observation introducing the phase-reference calibrator J1823−1228, the fringe-
finder DA 193 and the flux density calibrator 3C 286. Unfortunately, the phase-
reference calibrator was not detected and could not be used during the correlation.
The EVN observations were performed with the array described in Table 2.2.
Data were recorded in MkIV mode with 2-bit sampling at 256 Mbps at left hand
circular polarization, yielding a full bandwidth of 64 MHz (v6cm-256-8-2-L mode).
The data were correlated at the Joint Institute for VLBI in Europe (JIVE). An inte-
gration time of 4 s was used. Interferometer fringes for LS 5039 were detected in all
baselines. A later fringe fitting of the residual delays and fringe rates was performed
within aips. A first a priori visibility amplitude calibration was performed using
antenna gains and system temperatures measured at each antenna. We averaged
in frequency the data and exported them to be imaged and self-calibrated into the
difference mapping software difmap. The final imaging was carried out on those
data after editing and averaging of the visibilities in 32 s blocks.
MERLIN recorded data with 2-bit sampling at dual polarization and a total
13Published in Paredes, J. M., Ribó, M., Ros, E., Martí, J., & Massi, M. 2002, A&A, 393, L99.
14The European VLBI Network is a joint facility of European, Chinese and other radio astronomy
institutes funded by their national research councils.
15MERLIN is operated as a National Facility by the University of Manchester at Jodrell Bank
Observatory on behalf of the UK Particle Physics & Astronomy Research Council.