The X-ray jet in Centaurus A

Clues to the jet structure and particle acceleration

Jun Kataoka, Łukasz Stawarz, Felix Aharonian, Fumio Takahara, Michał Ostrowski, Philip G. Edwards

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S, 41 compact sources (mostly bright jet knots) were found within the jet on angular scales less than 4″, 13 of which were newly identified. We construct the luminosity function for the detected jet knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the sum of many unresolved fainter knots. We subtracted the contributions of the bright knots from the total X-ray jet flux, and show that the remaining extended emission has a relatively flat-topped intensity profile in the transverse jet direction, with the intensity peaking at the jet boundaries between 50″ and 170″. We note that limb-brightened morphologies have been observed previously at radio frequencies in a few FR I and FR II jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet, with an X-ray energy spectral index of αx ≈ 1, similar to those observed in the compact knots. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes, connected with the turbulent, supersonic, and nonsteady nature of the relativistic outflow. We note some evidence for a possible spectral hardening at the outer sheath of the jet, and manifesting itself in observed X-ray spectra of αx < 0.5 in the most extreme cases. Due to the limited photon statistics of the present data, further deep observations of Centaurus A are required to determine the reality of this finding; however, we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultrarelativistic particles within extragalactic jets.

Original languageEnglish
Pages (from-to)158-168
Number of pages11
JournalAstrophysical Journal
Volume641
Issue number1 I
DOIs
Publication statusPublished - 2006 Apr 10
Externally publishedYes

Fingerprint

particle acceleration
x rays
jet boundaries
particle
outflow
active galaxies
photons
limbs
sheaths
hardening
boundary layers
radio frequencies
shock
energy
luminosity
limb
statistics
shear
boundary layer

Keywords

  • Acceleration of particles
  • Galaxies: individual (Centaurus A)
  • Galaxies: jets radiation mechanisms: nonthermal
  • X-rays: general

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Kataoka, J., Stawarz, Ł., Aharonian, F., Takahara, F., Ostrowski, M., & Edwards, P. G. (2006). The X-ray jet in Centaurus A: Clues to the jet structure and particle acceleration. Astrophysical Journal, 641(1 I), 158-168. https://doi.org/10.1086/500407

The X-ray jet in Centaurus A : Clues to the jet structure and particle acceleration. / Kataoka, Jun; Stawarz, Łukasz; Aharonian, Felix; Takahara, Fumio; Ostrowski, Michał; Edwards, Philip G.

In: Astrophysical Journal, Vol. 641, No. 1 I, 10.04.2006, p. 158-168.

Research output: Contribution to journalArticle

Kataoka, J, Stawarz, Ł, Aharonian, F, Takahara, F, Ostrowski, M & Edwards, PG 2006, 'The X-ray jet in Centaurus A: Clues to the jet structure and particle acceleration', Astrophysical Journal, vol. 641, no. 1 I, pp. 158-168. https://doi.org/10.1086/500407
Kataoka J, Stawarz Ł, Aharonian F, Takahara F, Ostrowski M, Edwards PG. The X-ray jet in Centaurus A: Clues to the jet structure and particle acceleration. Astrophysical Journal. 2006 Apr 10;641(1 I):158-168. https://doi.org/10.1086/500407
Kataoka, Jun ; Stawarz, Łukasz ; Aharonian, Felix ; Takahara, Fumio ; Ostrowski, Michał ; Edwards, Philip G. / The X-ray jet in Centaurus A : Clues to the jet structure and particle acceleration. In: Astrophysical Journal. 2006 ; Vol. 641, No. 1 I. pp. 158-168.
@article{df285c7d5969471bb4719e840efe85db,
title = "The X-ray jet in Centaurus A: Clues to the jet structure and particle acceleration",
abstract = "We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S, 41 compact sources (mostly bright jet knots) were found within the jet on angular scales less than 4″, 13 of which were newly identified. We construct the luminosity function for the detected jet knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the sum of many unresolved fainter knots. We subtracted the contributions of the bright knots from the total X-ray jet flux, and show that the remaining extended emission has a relatively flat-topped intensity profile in the transverse jet direction, with the intensity peaking at the jet boundaries between 50″ and 170″. We note that limb-brightened morphologies have been observed previously at radio frequencies in a few FR I and FR II jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet, with an X-ray energy spectral index of αx ≈ 1, similar to those observed in the compact knots. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes, connected with the turbulent, supersonic, and nonsteady nature of the relativistic outflow. We note some evidence for a possible spectral hardening at the outer sheath of the jet, and manifesting itself in observed X-ray spectra of αx < 0.5 in the most extreme cases. Due to the limited photon statistics of the present data, further deep observations of Centaurus A are required to determine the reality of this finding; however, we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultrarelativistic particles within extragalactic jets.",
keywords = "Acceleration of particles, Galaxies: individual (Centaurus A), Galaxies: jets radiation mechanisms: nonthermal, X-rays: general",
author = "Jun Kataoka and Łukasz Stawarz and Felix Aharonian and Fumio Takahara and Michał Ostrowski and Edwards, {Philip G.}",
year = "2006",
month = "4",
day = "10",
doi = "10.1086/500407",
language = "English",
volume = "641",
pages = "158--168",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 I",

}

TY - JOUR

T1 - The X-ray jet in Centaurus A

T2 - Clues to the jet structure and particle acceleration

AU - Kataoka, Jun

AU - Stawarz, Łukasz

AU - Aharonian, Felix

AU - Takahara, Fumio

AU - Ostrowski, Michał

AU - Edwards, Philip G.

PY - 2006/4/10

Y1 - 2006/4/10

N2 - We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S, 41 compact sources (mostly bright jet knots) were found within the jet on angular scales less than 4″, 13 of which were newly identified. We construct the luminosity function for the detected jet knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the sum of many unresolved fainter knots. We subtracted the contributions of the bright knots from the total X-ray jet flux, and show that the remaining extended emission has a relatively flat-topped intensity profile in the transverse jet direction, with the intensity peaking at the jet boundaries between 50″ and 170″. We note that limb-brightened morphologies have been observed previously at radio frequencies in a few FR I and FR II jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet, with an X-ray energy spectral index of αx ≈ 1, similar to those observed in the compact knots. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes, connected with the turbulent, supersonic, and nonsteady nature of the relativistic outflow. We note some evidence for a possible spectral hardening at the outer sheath of the jet, and manifesting itself in observed X-ray spectra of αx < 0.5 in the most extreme cases. Due to the limited photon statistics of the present data, further deep observations of Centaurus A are required to determine the reality of this finding; however, we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultrarelativistic particles within extragalactic jets.

AB - We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S, 41 compact sources (mostly bright jet knots) were found within the jet on angular scales less than 4″, 13 of which were newly identified. We construct the luminosity function for the detected jet knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the sum of many unresolved fainter knots. We subtracted the contributions of the bright knots from the total X-ray jet flux, and show that the remaining extended emission has a relatively flat-topped intensity profile in the transverse jet direction, with the intensity peaking at the jet boundaries between 50″ and 170″. We note that limb-brightened morphologies have been observed previously at radio frequencies in a few FR I and FR II jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet, with an X-ray energy spectral index of αx ≈ 1, similar to those observed in the compact knots. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes, connected with the turbulent, supersonic, and nonsteady nature of the relativistic outflow. We note some evidence for a possible spectral hardening at the outer sheath of the jet, and manifesting itself in observed X-ray spectra of αx < 0.5 in the most extreme cases. Due to the limited photon statistics of the present data, further deep observations of Centaurus A are required to determine the reality of this finding; however, we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultrarelativistic particles within extragalactic jets.

KW - Acceleration of particles

KW - Galaxies: individual (Centaurus A)

KW - Galaxies: jets radiation mechanisms: nonthermal

KW - X-rays: general

UR - http://www.scopus.com/inward/record.url?scp=33744503471&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33744503471&partnerID=8YFLogxK

U2 - 10.1086/500407

DO - 10.1086/500407

M3 - Article

VL - 641

SP - 158

EP - 168

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 I

ER -