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

2.4. The radio counterpart: NVSS J182614−145054 51
Table 2.2: EVN array used in the LS 5039 observations.
Antenna Code Location Diameter DPFU (a) Tsys (b)
[m] [K Jy −1 ] [K]
Effelsberg EB Germany 100 1.47 27
Jodrell Bank JB U.K. 25 0.11 40
Cambridge CM U.K. 32 0.21 38
Westerbork WB Netherlands 14×25 1.0 67
Medicina MC Italy 32 0.15 53
Noto NT Italy 32 0.16 47
Toruń TR Poland 32 0.15 31
(a) Degrees per flux unit. (b) Best value during the experiment.
32 MHz bandwidth. We analyzed the left hand circular polarization data excluding
1 MHz channel at both edges of the band, yielding a final bandwidth of 14 MHz.
The correlator integration time was of 4 s. Standard reduction and imaging analysis
were carried out using aips and difmap.
To complement the amplitude calibration, we interleaved cross-scans (in azimuth
and elevation) with the 100 m Effelsberg antenna to measure the radio source flux
densities (A. Kraus, private communication). We fitted a Gaussian function to the
flux-density response for every cross-scan, and we averaged the different Gaussians.
We linked the flux density scale by observing primary calibrators such as 3C 286,
3C 48, or NGC 7027 (see e.g. Kraus 1997 or Peng et al. 2000).
Unfortunately, the flux density monitoring with the Effelsberg antenna was not
reliable due to contamination effects by the galactic plane diffuse emission and/or by
the close SNR G016.8−01.1. However, inspection of the shortest MERLIN baselines
reveals a constant flux density during the full run. That allowed us to image the
source directly without splitting the data in time blocks. We present the obtained
EVN and MERLIN images in Figs. 2.8 and 2.9, respectively. The MERLIN image is
presented convolved with a circular beam, equivalent in solid angle to the interfero-
metric synthesized beam of 142×46 mas at position angle (P.A.) 1.15 ◦ . Our images
clearly show that LS 5039 has a two-sided jet emanating from a central core. In
both images the southeast (SE) jet is brighter and larger than the northwest (NW)
one, as can be seen in Table 2.3, where we have quoted the flux densities of the core
and the jets and the lengths and P.A. of the jets. Their total lengths are ∼ 60 mas
in the EVN image and ∼ 300 mas in the MERLIN one.