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

2.4. The radio counterpart: NVSS J182614−145054 47
MilliARC SEC
4
2
0
-2
-4
-6
VLBA
6 4 2 0 -2 -4 -6
MilliARC SEC
Figure 2.6: VLBA self-calibrated image of LS 5039 at 5 GHz. Contours are 6, 8, 10,
12, 14, 16, 18, 20, 25, 30, 40, and 50 times 0.085 mJy beam −1 , the rms noise. The
synthesized beam, shown at the bottom right corner, is 3.4 mas×1.2 mas, with position
angle in 0 ◦ .
because there was no obvious nearby calibrator to be used. Data were recorded
in VLBA mode v6cm-256-8-2-L, i.e., at 6 cm wavelength, at 256 Mbps, using 8
baseband channels, with 2-bit sampling at left hand circular polarization, yielding
a full bandwidth of 64 MHz. The data were correlated at the VLBA correlator in
Socorro, New Mexico, using an integration time of 4 s. The LS 5039 coordinates
used for correlation were those obtained after the VLA A configuration observations,
i.e., α = 18 h 26 m 15.056 s , δ = −14 ◦ 50 ′ 54.24 ′′ , expressed in J2000.0 ICRS. The
output data were then calibrated using standard procedures in unconnected radio
interferometry within the aips and difmap software packages.
The resulting pattern of the observed visibility amplitudes, decaying as a function
of baseline length, indicated that LS 5039 had structure at milliarcsecond scales. The