2-6 September 2024
CJD Bonn Castell
Europe/Berlin timezone
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Contribution

CJD Bonn Castell

HST-1 knot: Results from quad-frequency observations of the M87 Jet

Speakers

  • Mr. Aleksei NIKONOV

Primary authors

Co-authors

Content

HST-1 is a knot in the conical kiloparsec-scale M87 jet, observed for the first time by the Hubble Space Telescope. In the images, it is the first the resolved feature near the jet's "core" on the arcsecond scale. HST-1 showed superluminal speeds up to 6c and significant flaring activity in optical and across all bands from radio to X-rays and even gamma-rays. Through the perspective of VLBI, the M87 jet exhibits a parabolic geometry, hinting at the significant role of HST-1 in the jet's collimation and evolution. However, due to its distance from the jet base and consequently, the smearing effects limiting the field of view for VLBI, HST-1 remains a challenging feature to study in detail, resulting in a lack of high-resolution VLBI data and spectral information.

In this talk, I will present our attempt to mitigate the problems introduced above using quad-frequency observations of HST-1 at 2, 5, 8, and 15 GHz with the VLBA and the EVN arrays. By utilizing these four frequencies, we have constructed a spectral index map of the knot and notably, a turnover frequency map for the first time.

The spectral index maps reveal a uniform structure with a steep spectrum slope of approximately -0.7, suggesting that HST-1 is likely part of an optically thin jet rather than a standing shock. The turnover frequency maps have also allowed us to estimate a magnetic field strength of the order of milliGauss.