Dynamics of rising magnetized cavities and ultrahigh energy cosmic ray acceleration in clusters of galaxies

Gourgouliatos, Konstantinos N.; Lyutikov, Maxim

doi:10.1111/j.1365-2966.2011.20058.x

Cited by 8 publications

(8 citation statements)

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“…It is important to emphasize that our finding regarding the plasma β parameter being of the order of unity in the giant lobes of Centaurus A may be crucial for understanding the dynamics and evolution of the reconnecting magnetic field in the system. Gourgouliatos & Lyutikov (2012) argued for example that the evolution of the expanding lobes containing some thermal plasma and some magnetic flux will always be accompanied by a decrease in the β parameter, leading at some point to the spontaneous formation of electric current sheets and large-scale reconnection layers which are likely involved in acceleration of the highest energy cosmic rays.…”

Section: Discussionmentioning

confidence: 99%

Giant Lobes of Centaurus a Radio Galaxy Observed With the Suzaku X-Ray Satellite

Stawarz

Tanaka

Madejski

et al. 2013

ApJ

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We report on Suzaku observations of selected regions within the Southern giant lobe of the radio galaxy Centaurus A. In our analysis we focus on distinct X-ray features detected with the X-ray Imaging Spectrometer within the range 0.5 − 10 keV, some of which are likely associated with fine structure of the lobe revealed by recent high-quality radio intensity and polarization maps. With the available photon statistics, we find that the spectral properties of the detected X-ray features are equally consistent with thermal emission from hot gas with temperatures kT > 1 keV, or with a power-law radiation continuum characterized by photon indices Γ ∼ 2.0 ± 0.5. However, the plasma parameters implied by these different models favor a synchrotron origin for the analyzed X-ray spots, indicating that a very efficient acceleration of electrons up to 10 TeV energies is taking place within the giant structure of Centaurus A, albeit only in isolated and compact regions associated with extended and highly polarized radio filaments. We also present a detailed analysis of the diffuse X-ray emission filling the whole field-of-view of the instrument, resulting in a tentative detection of a soft excess component best fitted by a thermal model with a temperature of kT ∼ 0.5 keV. The exact origin of the observed excess remains uncertain, although energetic considerations point to thermal gas filling the bulk of the volume of the lobe and mixed with the non-thermal plasma, rather than to the alternative scenario involving a condensation of the hot intergalactic medium around the edges of the expanding radio structure. If correct, this would be the first detection of the thermal content of the extended lobes of a radio galaxy in X-rays. The corresponding number density of the thermal gas in such a case is n g ∼ 10 −4 cm −3 , while its pressure appears to be in almost exact equipartition with the volume-averaged non-thermal pressure provided by the radio-emitting electrons and the lobes' magnetic field. A prominent large-scale fluctuation of the Galactic foreground emission, resulting in excess foreground X-ray emission aligned with the lobe, cannot be ruled out. Although tentative, our findings potentially imply that the structure of the extended lobes in active galaxies is likely to be highly inhomogeneous and non-uniform, with magnetic reconnection and turbulent acceleration processes continuously converting magnetic energy to internal energy of the plasma particles, leading to possibly significant spatial and temporal variations in the plasma β parameter around the volume-averaged equilibrium condition β ∼ 1.

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Section: Discussionmentioning

confidence: 99%

Giant Lobes of Centaurus a Radio Galaxy Observed With the Suzaku X-Ray Satellite

Stawarz

Tanaka

Madejski

et al. 2013

ApJ

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“…Several authors have suggested that self-organized, nearly force-free fields exist within radio lobes and cavities (e.g. [30,48]). These structures are the end point of magnetic (or Taylor) relaxation, which develops spontaneously if magnetic energy and helicity are injected into the system (e.g.…”

Section: From Theory: Inhomogeneous Modelsmentioning

confidence: 99%

The dynamic age of Centaurus A

Eilek

2014

New J. Phys.

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In this paper I present dynamic models of the radio source Centaurus A, and critique possible models of in situ particle reacceleration (ISR) within the radio lobes. The radio and γ-ray data require neither homogeneous plasma nor quasiequipartition between the plasma and magnetic field; inhomogeneous models containing both high-field and low-field regions are equally likely. Cen A cannot be as young as the radiative lifetimes of its relativistic electrons, which range from a few to several tens of Myr. Two classes of dynamic models-flow driven and magnetically driven-are consistent with current observations; each requires Cen A to be on the order of a Gyr old. Thus, ongoing ISR must be occuring within the radio source. Alfven-wave ISR is probably occuring throughout the source, and may be responsible for maintaining the γ-ray-loud electrons. This is likely to be supplemented by shock or reconnection ISR, which maintains the radio-loud electrons in high-field regions. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New J. Phys. 16 (2014) 045001 J A Eilek New J. Phys. 16 (2014) 045001 J A Eilek 3 IGM keV 413 dyn-− cm 2 . The likely density decay in the IGM between 100 and 300 kpc means p IGM is probably a bit higher around the inner part of the radio lobes, and a bit lower around the outer part. Conditions within the outer lobesIn order to evaluate the models of the outer lobes, we must understand their internal state. Our diagnostics are radio and γ-ray observations. Gamma rays detected by Fermi-LAT from the New J. Phys. 16 (2014) 045001 J A Eilek 4 1 gives a factor ≳10 increase in U e sy , ; this difference is due New J. Phys. 16 (2014) 045001 J A Eilek New J. Phys. 16 (2014) 045001 J A Eilek 7 3 I follow [60] in assuming that ν 1 is known; other authors, e.g. [54], do the calculation assuming γ 1 is known. Because ν 1 and γ 1 are related by the unknown B field, the algebra is different for each case; see [56] for details. New J. Phys. 16 (2014) 045001 J A Eilek 8 e sy , 57 erg and a magnetic New J. Phys. 16 (2014) 045001 J A Eilek 9, the leading term in P c would increase by 1.6; the second term inside brackets would decrease by 0.6. c c 2 , density ρ c and speed v c . New J. Phys. 16 (2014) 045001 J A Eilek

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“…A further important effect of the injected magnetic field will be to stabilize the bubble surfaces against fluid instabilities (e.g. Gourgouliatos & Lyutikov 2012).…”

Section: Implications Of Expelled Frozen-in Magnetic Fieldmentioning

confidence: 99%

Non-thermal insights on mass and energy flows through the Galactic Centre and into the Fermi bubbles

Crocker¹

2012

Monthly Notices of the Royal Astronomical Society

100

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We construct a simple model of the star‐formation‐ (and resultant supernova‐) driven mass and energy flows through the inner ∼200 pc (in diameter) of the Galaxy. Our modelling is constrained, in particular, by the non‐thermal radio continuum and γ‐ray signals detected from the region. The modelling points to a current star formation rate of 0.04–0.12 M⊙ yr−1 at 2σ confidence within the region with best‐fitting value in the range 0.08–0.12 M⊙ yr−1 which – if sustained over 10 Gyr – would fill out the ∼109 M⊙ stellar population of the nuclear bulge. Mass is being accreted on to the Galactic Centre (GC) region at a rate yr−1. The region’s star formation activity drives an outflow of plasma, cosmic rays and entrained, cooler gas. Neither the plasma nor the entrained gas reaches the gravitational escape speed, however, and all this material fountains back on to the inner Galaxy. The system we model can naturally account for the recently observed ≳106 M⊙‘halo’ of molecular gas surrounding the Central Molecular Zone out to 100–200 pc heights. The injection of cooler, high‐metallicity material into the Galactic halo above the GC may catalyze the subsequent cooling and condensation of hot plasma out of this region and explain the presence of relatively pristine, nuclear‐unprocessed gas in the GC. This process may also be an important ingredient in understanding the long‐term stability of the GC star formation rate. The plasma outflow from the GC reaches a height of a few kpc and is compellingly related to the recently discovered Fermi bubbles by a number of pieces of evidence. These include that the outflow advects precisely (i) the power in cosmic rays required to sustain the bubbles’γ‐ray luminosity in saturation; (ii) the hot gas required to compensate for gas cooling and drop‐out from the bubbles and (iii) the magnetic field required to stabilize the walls of these structures. Our modelling demonstrates that ∼109 M⊙ of hot gas is processed through the GC over 10 Gyr. We speculate that the continual star formation in the GC over the age of the Milky Way has kept the supermassive black hole in a quiescent state thus preventing it from significantly heating the coronal gas, allowing for the continual accretion of gas on to the disc and the sustenance of star formation on much wider scales in the Galaxy. In general, our investigations explicitly reveal the GC’s important role in the Milky Way’s wider stellar ecology.

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Dynamics of rising magnetized cavities and ultrahigh energy cosmic ray acceleration in clusters of galaxies

Cited by 8 publications

References 44 publications

Giant Lobes of Centaurus a Radio Galaxy Observed With the Suzaku X-Ray Satellite

Giant Lobes of Centaurus a Radio Galaxy Observed With the Suzaku X-Ray Satellite

The dynamic age of Centaurus A

Non-thermal insights on mass and energy flows through the Galactic Centre and into the Fermi bubbles

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