AIPS, the VLA, and the VLBA

Greisen, E. W.

doi:10.1007/0-306-48080-8_7

Cited by 674 publications

(329 citation statements)

References 21 publications

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“…The observations were taken in dual-polarization mode so that we could study the linear polarization of the jet as a probe of the underlying magnetic field structure. The data were correlated on the VLBA correlator and were processed with NRAO's Astronomical Imaging Processing System, AIPS, (Bridle & Greisen 1994;Greisen 1988) and the Caltech DIFMAP package (Shepherd, Pearson, & Taylor 1994, 1995 using standard techniques for VLBI polarization observations (e.g., Cotton 1993;Roberts, Wardle, & Brown 1994). The feed leakage terms were corrected using the strong, unpolarized source OQ208.…”

Section: Observations and Resultsmentioning

confidence: 99%

PKS 1510−089: A Head‐on View of a Relativistic Jet

Homan¹,

Wardle²,

Cheung³

et al. 2002

ApJ

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The gamma-ray blazar PKS 1510À089 has a highly superluminal milliarcsecond jet at a position angle (P.A.) of À28 and an arcsecond jet with an initial P.A. of 155 . With a DP.A. of 177 between the arcsecond and milliarcsecond jets, PKS 1510À089 is perhaps the most highly misaligned radio jet ever observed and serves as a graphic example of projection effects in a highly beamed relativistic jet. Here we present the results of observations designed to bridge the gap between the milliarcsecond and arcsecond scales. We find that a previously detected '' counterfeature '' to the arcsecond jet is directly fed by the milliarcsecond jet. This feature is located 0>3 from the core, corresponding to a deprojected distance of 30 kpc. The feature appears to be dominated by shocked emission and has an almost perfectly ordered magnetic field along its outside edge. We conclude that it is most likely a shocked bend, viewed end-on, where the jet crosses our line of sight to form the southern arcsecond jet. While the bend appears to be nearly 180 when viewed in projection, we estimate the intrinsic bending angle to be between 12 and 24 . The cause of the bend is uncertain; however, we favor a scenario where the jet is bent after it departs the galaxy, either by ram pressure due to winds in the intracluster medium or simply by the density gradient in the transition to the intergalactic medium.

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Section: Observations and Resultsmentioning

confidence: 99%

PKS 1510−089: A Head‐on View of a Relativistic Jet

Homan¹,

Wardle²,

Cheung³

et al. 2002

ApJ

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“…The initial calibration was performed with the NRAO Astronomical Image Processing System (AIPS) (Greisen 2003) following the standard techniques. All frequency bands were processed separately throughout the data reduction.…”

Section: Observations and Data Processingmentioning

confidence: 99%

MOJAVE: Monitoring of Jets in Active galactic nuclei with VLBA Experiments

Pushkarev

Hovatta

Kovalev

et al. 2012

A&A

247

296

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Aims. We have investigated a frequency-dependent shift in the absolute position of the optically thick apparent origin of parsec-scale jets ("core shift" effect) to probe physical conditions in ultra-compact relativistic outflows in active galactic nuclei. , and 88 μas, respectively, compared to the typical measured errors of 50, 51, 35 μas. The effect occurs predominantly along the jet direction, with departures smaller than 45 • from the median jet position angle in over 80% of the cases. Despite the moderate ratio of the observed frequencies (<2), core shifts significantly different from zero (>2σ) are detected for about 55% of the sources. These shifts are even better aligned with the jet direction, deviating from the latter by less than 30 • in over 90% of the cases. There is an indication that the core shift decreases with increasing redshift. Magnetic fields in the jet at a distance of 1 parsec from the central black hole, calculated from the obtained core shifts, are found to be systematically stronger in quasars (median B 1 ≈ 0.9 G) than those in BL Lacs (median B 1 ≈ 0.4 G). We also constrained the absolute distance of the core from the apex of the jet at 15 GHz as well as the magnetic field strength in the 15 GHz core region.

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“…Table 1 summarizes the parameters of our VLA observations. Data reduction, including calibration, deconvolution, and imaging, was carried out using the Astronomical Image Processing System (AIPS; Greisen 2003). After Doppler correcting the spectral-line data of DR21(OH), the frequency channel with the brightest maser emission signal was split off, and self-calibrated first in phase, then in both phase and amplitude, and imaged in a succession of iterative cycles.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

The Zeeman Effect in the 44 GHZ Class I Methanol Maser Line Toward Dr21(oh)

Momjian¹,

Sarma²

2017

ApJ

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We report detection of the Zeeman effect in the 44 GHz Class I methanol maser line, toward the star-forming region DR21(OH). In a 219 Jy beam −1 maser centered at an LSR velocity of 0.83 km s −1 , we find a 20-σ detection of zB los =53.5±2.7 Hz. If 44 GHz methanol masers are excited at n∼10 7-8 cm −3 , then the Bversusn 1/2 relation would imply, from comparison with Zeeman effect detections in the CN(1−0) line toward DR21(OH), that magnetic fields traced by 44 GHz methanol masers in DR21(OH) should be ∼10 mG. Combined with our detected zB los =53.5 Hz, this would imply that the value of the 44 GHz methanol Zeeman splitting factor z is ∼5 Hz mG −1 . Such small values of z would not be a surprise, as the methanol molecule is non-paramagnetic, like H 2 O. Empirical attempts to determine z, as demonstrated, are important because there currently are no laboratory measurements or theoretically calculated values of z for the 44 GHz CH 3 OH transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.

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AIPS, the VLA, and the VLBA

Cited by 674 publications

References 21 publications

PKS 1510−089: A Head‐on View of a Relativistic Jet

PKS 1510−089: A Head‐on View of a Relativistic Jet

MOJAVE: Monitoring of Jets in Active galactic nuclei with VLBA Experiments

The Zeeman Effect in the 44 GHZ Class I Methanol Maser Line Toward Dr21(oh)

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