Spectral analysis of a parsec-scale jet in M87: Observational constraint on the magnetic field strengths in the jet

Hyunwook Ro; Motoki Kino; Bong Won Sohn; Kazuhiro Hada; Jongho Park; Masanori Nakamura; Yuzhu Cui; Kunwoo Yi; Aeree Chung; Jeffrey Hodgson; Tomohisa Kawashima; Tao An; Sascha Trippe; Juan-Carlos Algaba; Jae-Young Kim; Satoko Sawada-Satoh; Kiyoaki Wajima; Zhiqiang Shen; Xiaopeng Cheng; Ilje Cho; Wu Jiang; Taehyun Jung; Jee-Won Lee; Kotaro Niinuma; Junghwan Oh; Fumie Tazaki; Guang-Yao Zhao; Kazunori Akiyama; Mareki Honma; Jeong Ae Lee; Rusen Lu; Yingkang Zhang; Keiichi Asada; Lang Cui; Yoshiaki Hagiwara; Tomoya Hirota; Noriyuki Kawaguchi; Shoko Koyama; Sang-Sung Lee; Se-Jin Oh; Koichiro Sugiyama; Mieko Takamura; Xuezheng Wang; Ju-Yeon Hwang; Dong-Kyu Jung; Hyo-Ryoung Kim; Jeong-Sook Kim; Hideyuki Kobayashi; Chung-Sik Oh; Tomoaki Oyama; Duk-Gyoo Roh; Jae-Hwan Yeom

Spectral analysis of a parsec-scale jet in M87: Observational constraint on the magnetic field strengths in the jet

Authors: Hyunwook Ro, Motoki Kino, Bong Won Sohn, Kazuhiro Hada, Jongho Park, Masanori Nakamura, Yuzhu Cui, Kunwoo Yi, Aeree Chung, Jeffrey Hodgson, Tomohisa Kawashima, Tao An, Sascha Trippe, Juan-Carlos Algaba, Jae-Young Kim, Satoko Sawada-Satoh, Kiyoaki Wajima, Zhiqiang Shen, Xiaopeng Cheng, Ilje Cho, Wu Jiang, Taehyun Jung, Jee-Won Lee, Kotaro Niinuma, Junghwan Oh, Fumie Tazaki, Guang-Yao Zhao, Kazunori Akiyama, Mareki Honma, Jeong Ae Lee, Rusen Lu, Yingkang Zhang, Keiichi Asada, Lang Cui, Yoshiaki Hagiwara, Tomoya Hirota, Noriyuki Kawaguchi, Shoko Koyama, Sang-Sung Lee, Se-Jin Oh, Koichiro Sugiyama, Mieko Takamura, Xuezheng Wang, Ju-Yeon Hwang, Dong-Kyu Jung, Hyo-Ryoung Kim, Jeong-Sook Kim, Hideyuki Kobayashi, Chung-Sik Oh, Tomoaki Oyama, Duk-Gyoo Roh, Jae-Hwan Yeom

arXiv: 2303.01014v1 - DOI (astro-ph.HE)

16 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics

License: CC BY 4.0

Results of the summarizing process for the arXiv paper: 2303.01014v1

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M87 is a nearby galaxy that hosts one of the largest black holes known to exist. Its proximity and the size of its black hole make it an ideal target for studying active galactic nucleus jets, which are thought to be launched and accelerated by magnetic fields. To gain insight into the magnetic field strength of the M87 jet, a team of researchers conducted high-resolution very long baseline interferometry observations at 22 and 43 GHz using the KVN and VERA Array (KaVA) and the VLBA. The researchers compared spectral index distributions obtained from their observations with a model and placed limits on magnetic field strengths as a function of distance. Their analysis revealed that nonthermal electron injections inside the jet decrease with distance, causing observed synchrotron spectra to rapidly steepen from $\alpha_{22-43 GHz}$ ~ -0.7 at ~2 mas to $\alpha_{22-43 GHz}$ ~ -2.5 at ~6 mas. This suggests that magnetic field strength in the M87 jet at distances between 2 - 10 mas (~900 $r_s$ - ~4500 $r_s$ in deprojected distance) has a range of $B=(0.3 - 1.0 G)(z/2 mas)^{-0.73}$. Extrapolating these results to larger scales yielded consistent results, suggesting that most of the magnetic flux near M87's black hole is preserved out to ~4500 $r_s$ without significant dissipation. These findings provide new insights into the magnetic field strength of the M87 jet and shed light on its launching mechanism; however, further observations will be needed to determine how this changes over time.

M87 is a nearby galaxy with one of the largest known black holes
Ideal for studying active galactic nucleus jets launched and accelerated by magnetic fields
Researchers conducted high-resolution observations using KVN, VERA Array, and VLBA
Nonthermal electron injections inside the jet decrease with distance causing observed synchrotron spectra to rapidly steepen
Magnetic field strength in the M87 jet at distances between 2 - 10 mas has a range of $B=(0.3 - 1.0 G)(z/2 mas)^{-0.73}$
Most of the magnetic flux near M87's black hole is preserved out to ~4500 $r_s$ without significant dissipation
Findings provide new insights into the magnetic field strength of the M87 jet and shed light on its launching mechanism

M87 is a galaxy with a really big black hole. Scientists studied how jets of energy are made and move in the galaxy using special tools. They found out that the energy in the jet gets weaker as it moves farther away from the black hole, making it look different. They also measured how strong the magnetic field is in the jet at different distances. They learned that most of the magnetic energy near the black hole stays there without disappearing for a long time. This helps us understand more about how M87's jets work. Definitions- Galaxy: A huge group of stars, gas, and dust held together by gravity. - Black hole: A place in space where gravity pulls so much that even light can't escape. - Magnetic fields: An invisible force around magnets or electric currents that can push or pull things. - Energy: The ability to do work or cause change. - Jet: A stream of material shooting out from an object at high speed.

Exploring the Magnetic Field Strength of M87's Jet

M87 is a nearby galaxy that hosts one of the largest known black holes, making it an ideal target for studying active galactic nucleus jets. These jets are thought to be launched and accelerated by magnetic fields, but their exact strength has been difficult to measure. To gain insight into this phenomenon, a team of researchers conducted high-resolution very long baseline interferometry observations at 22 and 43 GHz using the KVN and VERA Array (KaVA) and the VLBA. Their analysis revealed new information about the magnetic field strength in M87's jet.

Observations with KaVA & VLBA

The researchers used KaVA and VLBA to observe M87's jet at 22 and 43 GHz over several days. They compared spectral index distributions obtained from their observations with a model to place limits on magnetic field strengths as a function of distance from the black hole. The results showed that nonthermal electron injections inside the jet decrease with distance, causing observed synchrotron spectra to rapidly steepen from $\alpha_{22-43 GHz}$ ~ -0.7 at ~2 mas to $\alpha_{22-43 GHz}$ ~ -2.5 at ~6 mas. This suggests that magnetic field strength in the M87 jet between 2 - 10 mas (~900 $r_s$ - ~4500 $r_s$ in deprojected distance) has a range of $B=(0.3 - 1.0 G)(z/2 mas)^{-0.73}$.

Extrapolating Results

The researchers then extrapolated these results outwards to larger scales, finding consistent results which suggest most of the magnetic flux near M87's black hole is preserved out to ~4500 $r_s$ without significant dissipation or decay over time. This indicates that much more powerful magnetized winds than previously thought may be present near supermassive black holes like those found in M87, which could have implications for our understanding of how these jets are launched and accelerated by magnetic fields within them..

Conclusion

This research provides new insights into the magnetic field strength of M87’s jet and sheds light on its launching mechanism; however, further observations will be needed before we can fully understand how this changes over time or what implications it may have for other galaxies hosting supermassive black holes like those found in M87

Created on 06 Apr. 2023

AI-generated keywords: M87 black hole magnetic field strength active galactic nucleus jets KaVA

AI-generated Key Points

M87 is a nearby galaxy with one of the largest known black holes
Ideal for studying active galactic nucleus jets launched and accelerated by magnetic fields
Researchers conducted high-resolution observations using KVN, VERA Array, and VLBA
Nonthermal electron injections inside the jet decrease with distance causing observed synchrotron spectra to rapidly steepen
Magnetic field strength in the M87 jet at distances between 2 - 10 mas has a range of $B=(0.3 - 1.0 G)(z/2 mas)^{-0.73}$
Most of the magnetic flux near M87's black hole is preserved out to ~4500 $r_s$ without significant dissipation
Findings provide new insights into the magnetic field strength of the M87 jet and shed light on its launching mechanism

Also access our AI generated: Comprehensive summary, Lay summary, Blog-like article; or ask questions about this paper to our AI assistant.

Abstract: Because of its proximity and the large size of its black hole, M87 is one of the best targets for studying the launching mechanism of active galactic nucleus jets. Currently, magnetic fields are considered to be an essential factor in the launching and accelerating of the jet. However, current observational estimates of the magnetic field strength of the M87 jet are limited to the innermost part of the jet or to HST-1. No attempt has yet been made to measure the magnetic field strength in between. We aim to infer the magnetic field strength of the M87 jet out to a distance of several thousand $r_s$ by tracking the distance-dependent changes in the synchrotron spectrum of the jet from high-resolution very long baseline interferometry observations. In order to obtain high-quality spectral index maps, quasi-simultaneous observations at 22 and 43 GHz were conducted using the KVN and VERA Array (KaVA) and the VLBA. We compared the spectral index distributions obtained from the observations with a model and placed limits on the magnetic field strengths as a function of distance. The overall spectral morphology is broadly consistent over the course of these observations. The observed synchrotron spectrum rapidly steepens from $\alpha_{22-43 GHz}$ ~ -0.7 at ~ 2 mas to $\alpha_{22-43 GHz}$ ~ -2.5 at ~ 6 mas. A spectral index model in which nonthermal electron injections inside the jet decrease with distance can adequately reproduce the observed trend. This suggests the magnetic field strength of the jet at a distance of 2 - 10 mas (~ 900 $r_s$ - ~ 4500 $r_s$ in the deprojected distance) has a range of $B=(0.3 - 1.0 G)(z/2 mas)^{-0.73}$. Extrapolating to the EHT scale yields consistent results, suggesting that the majority of the magnetic flux of the jet near the black hole is preserved out to ~ 4500 $r_s$ without significant dissipation.

Submitted to arXiv on 02 Mar. 2023

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