Abstract
We present total and linearly polarized 3 mm Global mm-VLBI Array (GMVA; mm-VLBI: Very Long Baseline Interferometry observations at millimetre wavelengths) images of a sample of blazars and radio galaxies from the VLBA-BU-BLAZAR 7 mm monitoring program designed to probe the innermost regions of active galactic nuclei (AGN) jets and locate the sites of gamma-ray emission observed by the Fermi-LAT. The lower opacity at 3 mm and improved angular resolution—on the order of 50 microarcseconds—allow us to distinguish features in the jet not visible in the 7 mm VLBA data. We also compare two different methods used for the calibration of instrumental polarisation and we analyze the resulting images for some of the sources in the sample.
Highlights
Combining long baselines and short observing wavelength, Very Long Baseline Interferometry observations at millimetre wavelengths provide very high spatial resolution images.the reduced opacity at 3 mm allows us to investigate regions that are optically thick at longer wavelengths, such as the jet formation regions in the vicinity of supermassive black holes
The Global mm-VLBI Array (GMVA) program was started in 2008, consists of one or two observations per year of roughly half of the active galactic nuclei (AGN) in the VLBA-BU-BLAZAR sample, and is aimed at relating the gamma-ray emission observed in these objects to physical conditions and structure in the mm-wave core region
1510-089 and CTA 102, and certainly worse than that of OJ 287, plus some sources have more complex polarized substructures, we decided to calibrate the instrumental polarization using the average D-terms. This approach has the significant advantage of obtaining the final D-term values to apply by taking into account a large number of source measurements and one. This is of particular importance for a mm-VLBI dataset, where the choice of a calibrator for the polarization is not trivial and depends on the quality of data
Summary
Combining long baselines and short observing wavelength, Very Long Baseline Interferometry observations at millimetre wavelengths (mm-VLBI) provide very high spatial resolution images. The Global mm-VLBI Array (GMVA), observing at 3 mm (86 GHz), is currently the main source of high-resolution total and polarized intensity images of active galactic nuclei (AGN) at short millimeter wavelengths. We present some 86 GHz GMVA images in both total and linearly polarized intensity of a sample of bright and gamma-ray loud blazars taken on 21 May 2016 within a program The GMVA program was started in 2008, consists of one or two observations per year of roughly half of the AGN in the VLBA-BU-BLAZAR sample, and is aimed at relating the gamma-ray emission observed in these objects to physical conditions and structure in the mm-wave core region. Information about the program as well as some preliminary results can be found at http://www.bu.edu/blazars/vlbi3mm/, as well as in [3,4]
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