RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz
Abstract
We present RadioAstron observations of the M87 jet obtained on 2014 February 4-5 at 4.8 GHz (λ=6.2 cm). The correlated signals between the 10-m space antenna and ground-based radio telescopes were detected up to projected baselines of thicksim3\,Earth diameters (0.65~Gλ). The orientation of the jet downstream of the core shifts northward, consistent with the long-term oscillating trend reported in other studies. An elliptical body mode of the Kelvin-Helmholtz instability can create the observed helical shape of the jet. The estimated wavelength of this instability mode suggests that its origin may be related to some processes in the accretion disc. We present 1.7 - 4.8 GHz and 4.8 - 15.4 GHz spectral index maps showing flattening of the spectrum along the outer streamlines and along the jet spine. Simulations and analysis show that this spectral flattening is partially artificial and is a common systematic effect of the CLEAN procedure of VLBI imaging. The spectral index of the M87 jet is consistent with the optically thin emission, while its steepening can be produced by the propagation of the instability modes causing higher pressure regions near the jet boundary and in its interior.
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BibTeX
@misc{kravchenko2026radioastron,
title = {{RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz}},
author = {Evgeniya V. Kravchenko and Tuomas Savolainen and Alexey S. Nikonov and Ilya N. Pashchenko and Elena E. Nokhrina and Petr A. Voitsik and Leonid I. Gurvits and Yuri Y. Kovalev and Jae-Young Kim and Mikhail M. Lisakov and Andrei P. Lobanov and Kirill V. Sokolovsky},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18192},
eprint = {2609.18192},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18192},
}
RIS
TY - UNPB
TI - RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz
AU - Evgeniya V. Kravchenko
AU - Tuomas Savolainen
AU - Alexey S. Nikonov
AU - Ilya N. Pashchenko
AU - Elena E. Nokhrina
AU - Petr A. Voitsik
AU - Leonid I. Gurvits
AU - Yuri Y. Kovalev
AU - Jae-Young Kim
AU - Mikhail M. Lisakov
AU - Andrei P. Lobanov
AU - Kirill V. Sokolovsky
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.18192
UR - https://arxiv.org/abs/2609.18192
AB - We present RadioAstron observations of the M87 jet obtained on 2014 February 4-5 at 4.8 GHz (λ=6.2 cm). The correlated signals between the 10-m space antenna and ground-based radio telescopes were detected up to projected baselines of thicksim3\,Earth diameters (0.65~Gλ). The orientation of the jet downstream of the core shifts northward, consistent with the long-term oscillating trend reported in other studies. An elliptical body mode of the Kelvin-Helmholtz instability can create the observed helical shape of the jet. The estimated wavelength of this instability mode suggests that its origin may be related to some processes in the accretion disc. We present 1.7 - 4.8 GHz and 4.8 - 15.4 GHz spectral index maps showing flattening of the spectrum along the outer streamlines and along the jet spine. Simulations and analysis show that this spectral flattening is partially artificial and is a common systematic effect of the CLEAN procedure of VLBI imaging. The spectral index of the M87 jet is consistent with the optically thin emission, while its steepening can be produced by the propagation of the instability modes causing higher pressure regions near the jet boundary and in its interior.
ER -