Soft X-Ray and Extreme Ultraviolet Excess Emission from Clusters of Galaxies

Durret, F.; Kaastra, J. S.; Nevalainen, J.; Ohashi, T.; Werner, Norbert

doi:10.1007/s11214-008-9313-8

Cited by 36 publications

(34 citation statements)

References 80 publications

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“…Our results have clear implications for the interpretation of ‘soft‐excess’ X‐ray emission from galaxy clusters (e.g. Durret et al 2008 and references therein) and show that apparently soft excesses (or best‐fitting absorption of less than the Galactic value) can arise from inadequate modelling of the emission spectra in the presence of significant spatial variations in temperature and metallicity, as well as additional emission components.…”

Section: Discussionmentioning

confidence: 66%

“…Lieu et al 1996; Bowyer, Berghöfer & Korpela 1999; Arabadjis & Bregman 2000; Bonamente, Lieu & Mittaz 2001; Bonamente, Joy & Lieu 2003; Finoguenov, Briel & Henry 2003; Bowyer et al 2004), for other systems, claims of diffuse UV emission over and above that expected from the intracluster plasma remain controversial (see e.g. Bregman & Lloyed‐Davies 2006; see also Durret et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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Chandrameasurements of non-thermal-like X-ray emission from massive, merging, radio halo clusters

Million

Allen

2009

Monthly Notices of the Royal Astronomical Society

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We report the discovery of spatially extended, non‐thermal‐like emission components in Chandra X‐ray spectra for five of a sample of seven massive, merging galaxy clusters with powerful radio haloes. The emission components can be fitted by power‐law models with mean photon indices in the range 1.5 < Γ < 2.0. A control sample of regular, dynamically relaxed clusters, without radio haloes but with comparable mean thermal temperatures and luminosities, shows no compelling evidence for similar components. Detailed X‐ray spectral mapping reveals the complex thermodynamic states of the radio halo clusters. Our deepest observations, of the Bullet Cluster 1E 0657−56, demonstrate a spatial correlation between the strongest power‐law X‐ray emission, highest thermal pressure and brightest 1.34 GHz radio halo emission in this cluster. We confirm the presence of a shock front in the 1E 0657−56 and report the discovery of a new, large‐scale shock front in Abell 2219. We explore possible origins for the power‐law X‐ray components. These include inverse‐Compton scattering of cosmic microwave background photons by relativistic electrons in the clusters; bremsstrahlung from suprathermal electrons energized by Coulomb collisions with an energetic, non‐thermal proton population; and synchrotron emission associated with ultrarelativistic electrons. Interestingly, we show that the power‐law signatures may also be due to complex temperature and/or metallicity structure in clusters particularly in the presence of metallicity gradients. In this case, an important distinguishing characteristic between the radio halo clusters and control sample of predominantly cool‐core clusters is the relatively low central X‐ray surface brightness of the former. Our results have implications for previous discussions of soft excess X‐ray emission from clusters and highlight the importance of further deep X‐ray and radio mapping, coupled with new hard X‐ray, γ‐ray and TeV observations, for improving our understanding of the non‐thermal particle populations in these systems.

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Section: Discussionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Chandrameasurements of non-thermal-like X-ray emission from massive, merging, radio halo clusters

Million

Allen

2009

Monthly Notices of the Royal Astronomical Society

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“…We therefore need around 3 × 10 −5 of the axions to convert into photons for this energy in order to understand the 3/4 keV background as being due to dark axions. Note this spectrum, originally plotted in reference [13], peaks around 200 eV to try and offer a very exciting possible solution to the soft X-ray galaxy cluster excess [21,20]. Because of this, it is natural to consider slightly different moduli masses with energy spectra which could peak in the 650-1keV region.…”

Section: Dark Radiation Fluxmentioning

confidence: 99%

Axionic dark radiation and the Milky Way’s magnetic field

Fairbairn

2014

Phys. Rev. D

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Recently it has been suggested that dark radiation in the form of axions produced during the decay of string theory moduli fields could be responsible for the soft x-ray excess in galaxy clusters. These soft X-ray photons come about due to the conversion of these axions into photons in the magnetic fields of the clusters. In this work we calculate the conversion of axionic dark radiation into X-ray photons in the magnetic field of our own Galaxy. We consider ∆N ν ∼ 0.5 worth of dark radiation made up of axions with energy of order 0.1-1 keV. We show that it is possible, if a little optimistic, to explain the large regions of X-ray emission located above and below the centre of the Galactic plane detected in the 3/4 keV ROSAT all sky map completely due to the conversion of dark radiation into photons with an inverse axion-photon coupling of M ∼ 3 × 10 13 GeV and an axion mass of m ≤ 10 −12 eV. Different parameter values could explain both these features and the 3/4 keV X-ray background. More conservatively, these X-ray observations are a good way to constrain such models of axionic dark radiation.

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“…While the diffuse radio sources in galaxy clusters are universally interpreted as produced by synchrotron emission, the extreme ultraviolet (EUV) and hard X-ray (HXR) excesses have been interpreted as the combined effect of an underlying inverseCompton scattering (ICS) of the cosmic microwave background (CMB) against cluster relativistic electrons that complement the radio halo population (e.g., Hwang 1997;Ensslin & Biermann 1998;Sarazin & Lieu 1998;Blasi & Colafrancesco 1999;Colafrancesco et al 2007;Marchegiani et al 2007;Colafrancesco & Marchegiani 2009;Buote 2001), or thermal emission (Mittaz et al 1998;Cen & Ostriker 1999) from "missing baryons" at sub-virial temperatures (see, e.g., the review of Durret et al 2008). Focusing upon the former interpretation, the role and ramifications of an underlying power law spectrum across the entire X-ray frequency band can be far reaching, with issues concerning cluster merging and central cooling, and also mass and spectroscopic consequences being addressed by Million & Allen (2009), Lagana et al (2010), andProkhorov (2009).…”

Section: Introductionmentioning

confidence: 99%

Dark matter interpretation of the origin of non-thermal phenomena in galaxy clusters

Colafrancesco

Lieu

Marchegiani

et al. 2011

A&A

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Aims. We studied the multi-frequency predictions of various annihilating dark matter (DM) scenarios in order to explore the possibility to interpret the still unknown origin of non-thermal phenomena in galaxy clusters. Methods. We consider three different DM models with light (9 GeV), intermediate (60 GeV), and high (500 GeV) neutralino mass and study their physical effects in the atmosphere of the Coma cluster. The secondary particles created in the neutralino annihilation processes produce a multi-frequency spectral energy distribution (SED) of non-thermal radiation and also heat the intracluster gas, which we test against the observations available for the Coma cluster from radio to gamma-rays. The various DM-produced SEDs are normalized by the condition to fit the Coma radio halo spectrum, thus obtaining best-fit values of the annihilation cross-section σV and of the central magnetic field B 0 . Results. We find that it is not possible to interpret all the non-thermal phenomena observed in galaxy clusters in terms of DM annihilation. The light-mass DM model with 9 GeV mass produces too little power at all other frequencies, while the high-mass DM model with 500 GeV produces a large excess power at all other frequencies. The intermediate-mass DM model with 60 GeV and τ ± composition is marginally consistent with the HXR and gamma-ray observations, but narrowly fails to reproduce the EUV and soft X-ray observations. The intermediate-mass DM model with 60 GeV and bb composition is, on the other hand, always below the observed fluxes. We note that the radio halo spectrum of Coma is well fitted only in the bb or light-and intermediate-mass DM models. We also find that the heating produced by the DM annihilation in the centre of the Coma cluster is always larger than the intracluster gas cooling rate for an NFW DM density profile and it is substantially smaller than the cooling rate only for a cored DM density profile in light-mass DM model with 9 GeV. Conclusions. The possibility of interpreting the origin of non-thermal phenomena in galaxy clusters with DM annihilation scenarios requires a low neutralino mass and a cored DM density profile. If we then consider the multi-messenger constraints to the neutralino annihilation cross-section, it turns out that this scenario would also be excluded unless we introduce a substantial boost factor that represents DM substructures. If we relax the condition to fit the Coma radio halo and we consider the EUV and HXR detections as upper limits for the non-thermal emission, together with the gamma-ray limit, then the limits on σV are less stringent than those obtained by the multi-messenger analysis.

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Soft X-Ray and Extreme Ultraviolet Excess Emission from Clusters of Galaxies

Cited by 36 publications

References 80 publications

Chandrameasurements of non-thermal-like X-ray emission from massive, merging, radio halo clusters

Chandrameasurements of non-thermal-like X-ray emission from massive, merging, radio halo clusters

Axionic dark radiation and the Milky Way’s magnetic field

Dark matter interpretation of the origin of non-thermal phenomena in galaxy clusters

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