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Probing the innermost regions of AGN jets and their magnetic fields with RadioAstron. I. Imaging BL Lacertae at 21 microarcsecond resolution | | José L. Gómez
; Andrei P. Lobanov
; Gabriele Bruni
; Yuri Y. Kovalev
; Alan P. Marscher
; Svetlana G. Jorstad
; Yosuke Mizuno
; Uwe Bach
; Kirill V. Sokolovsky
; James M. Anderson
; Pablo Galindo
; Nikolay S. Kardashev
; Mikhail M. Lisakov
; | | Date: |
15 Dec 2015 | | Abstract: | We present the first polarimetric space VLBI imaging observations at 22 GHz.
BL Lacertae was observed in 2013 November 10 with the RadioAstron space VLBI
mission, including a ground array of 15 radio telescopes. The instrumental
polarization of the space radio telescope is found to be within 9%,
demonstrating the polarimetric imaging capabilities of RadioAstron at 22 GHz.
Ground-space fringes were obtained up to a projected baseline distance of 7.9
Earth’s diameters in length, allowing us to image the jet in BL Lacertae with a
maximum angular resolution of 21 $mu$as, the highest achieved to date. We find
evidence for emission upstream of the radio core, which may correspond to a
recollimation shock at about 40 $mu$as from the jet apex, in a pattern that
includes other recollimation shocks at approximately 100 $mu$as and 250
$mu$as from the jet apex. Polarized emission is detected in two components
within the innermost 0.5 mas from the core, as well as in some knots 3 mas
downstream. Faraday rotation analysis, obtained from combining RadioAstron 22
GHz and ground-based 15 GHz and 43 GHz images, shows a gradient in rotation
measure and Faraday corrected polarization vector as a function of position
angle with respect to the core, suggesting that the jet in BL Lacertae is
threaded by a helical magnetic field. The intrinsic de-boosted brightness
temperature in the unresolved core exceeds $3! imes!10^{12}$ K, suggesting
at the very least departure from equipartition of energy between the magnetic
field and radiating particles. | | Source: | arXiv, 1512.4690 | | Services: | Forum | Review | PDF | Favorites | |
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