8 research outputs found
Parsec-scale radio structures in the nuclei of four Seyfert galaxies
We present 18-cm radio maps of four Seyfert nuclei, Mrk 1, Mrk 3, Mrk 231 and
Mrk 463E, made with the European VLBI Network (EVN). Linear radio structures
are present in three out of four sources on scales of ~100 pc to ~1 kpc, and
the 20-mas beam of the EVN enables us to resolve details within the radio
structures on scales of <10 pc. Mrk 3 was also imaged using MERLIN and the data
combined with the EVN data to improve the sensitivity to extended emission. We
find an unresolved flat-spectrum core in Mrk 3, which we identify with the
hidden Seyfert 1 nucleus in this object, and we also see marked differences
between the two highly-collimated radio jets emanating from the core. The
western jet terminates in a bright hotspot and resembles an FRII radio
structure, whilst the eastern jet has more in common with an FRI source. In Mrk
463E, we use the radio and optical structure of the source to argue that the
true nucleus lies approximately 1 arcsec south of the position of the radio and
optical brightness peaks, which probably represent a hotspot at the working
surface of a radio jet. The EVN data also provide new evidence for a 100-pc
radio jet powering the radio source in the Type 1 nucleus of Mrk 231. However,
the Seyfert 2 galaxy Mrk 1 shows no evidence for radio jets down to the limits
of resolution (~10 pc). We discuss the range of radio source size and
morphology which can occur in the nuclei of Seyfert galaxies and the
implications for Seyfert unification schemes and for radio surveys of large
samples of objects.Comment: 23 pages, 7 postscript figures (supplied as separate files), uses AAS
aaspp4 LaTeX style file, to appear in the 10 June 1999 issue of The
Astrophysical Journa
A very brief description of LOFAR - the Low Frequency Array
LOFAR (Low Frequency Array) is an innovative radio telescope optimized for
the frequency range 30-240 MHz. The telescope is realized as a phased aperture
array without any moving parts. Digital beam forming allows the telescope to
point to any part of the sky within a second. Transient buffering makes
retrospective imaging of explosive short-term events possible. The scientific
focus of LOFAR will initially be on four key science projects (KSPs): 1)
detection of the formation of the very first stars and galaxies in the universe
during the so-called epoch of reionization by measuring the power spectrum of
the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ~5' scale; 2)
low-frequency surveys of the sky with of order expected new sources; 3)
all-sky monitoring and detection of transient radio sources such as gamma-ray
bursts, x-ray binaries, and exo-planets (Farrell et al. 2004); and 4) radio
detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003)
allowing for the first time access to particles beyond 10^21 eV (Scholten et
al. 2006). Apart from the KSPs open access for smaller projects is also
planned. Here we give a brief description of the telescope.Comment: 2 pages, IAU GA 2006, Highlights of Astronomy, Volume 14, K.A. van
der Hucht, e
Constraining the radio jet proper motion of the high-redshift quasar J2134-0419 at z = 4.3
To date, PMN J2134-0419 (at a redshift z = 4.33) is the second most distant quasar known with a milliarcsecond-scale morphology permitting direct estimates of the jet proper motion. Based on two-epoch observations, we constrained its radio jet proper motion using the very long baseline interferometry (VLBI) technique. The observations were conducted with the European VLBI Network (EVN) at 5 GHz on 1999 November 26 and 2015 October 6. We imaged the central 10-pc scale radio jet emission and modeled its brightness distribution. By identifying a jet component at both epochs separated by 15.86 yr, a proper motion of μ = 0.035 ± 0.023 mas yr-1 is found. It corresponds to an apparent superluminal speed of βa = 4.1 ± 2.7 c. Relativistic beaming at both epochs suggests that the jet viewing angle with respect to the line of sight is smaller than 20°, with a minimum bulk Lorentz factor Γ = 4.3. The small value of the proper motion is in good agreement with the expectations from the cosmological interpretation of the redshift and the current cosmological model. Additionally we analyzed archival Very Large Array observations of J2143-0419 and found indication of a bent jet extending to ˜30 kpc