On the inverse Compton scattering interpretation of the hard X-ray excesses in galaxy clusters: the case of Ophiuchus

Colafrancesco, S.; Marchegiani, ¶.

doi:10.1051/0004-6361/200911843

Cited by 21 publications

(17 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ferrari et al 2008): i) primary old merger and subsequent re-accelerations due to turbulence or ii) secondary hardonic collisions. In Ophiuchus, the secondary acceleration models due to hadron-hadron collisions are inconsistent with the available hard X-ray measurements (Colafrancesco & Marchegiani 2009). A viable scenario for the Ophiuchus cluster is that the primary merger happened sufficiently long time ago (as required by the long cooling time) so that most merger signatures have disappeared and that the relativistic electron population was later reaccelerated by the MHD turbulence.…”

Section: Resultsmentioning

confidence: 99%

XMM-Newton and INTEGRAL analysis of the Ophiuchus cluster of galaxies

Nevalainen¹,

Eckert

Kaastra

et al. 2009

A&A

View full text Add to dashboard Cite

Aims. We investigated the non-thermal hard X-ray emission in the Ophiuchus cluster of galaxies. Our aim is to characterise the physical properties of the non-thermal component and its interaction with the cosmic microwave background. Methods. We performed spatially resolved spectroscopy and imaging using XMM-Newton data to model the thermal emission. Combining this with INTEGRAL ISGRI data, we modelled the 0.6−140 keV band total emission in the central 7 arcmin region.Results. The models that best describe both PN and ISGRI data contain a power-law component with a photon index in a range 2.2−2.5. This component produces ∼10% of the total flux in the 1−10 keV band. The pressure of the non-thermal electrons is ∼1% of that of the thermal electrons. Our results support the scenario whereby a relativistic electron population, which produces the recently detected radio mini-halo in Ophiuchus, also produces the hard X-rays via inverse compton scattering of the CMB photons. The best-fit models imply a differential momentum spectrum of the relativistic electrons with a slope of 3.4−4.0 and a magnetic field strength B = 0.05−0.15 μG. The lack of evidence for a recent major merger in the Ophiuchus centre allows the possibility that the relativistic electrons are produced by turbulence or hadronic collisions.

show abstract

Section: Resultsmentioning

confidence: 99%

XMM-Newton and INTEGRAL analysis of the Ophiuchus cluster of galaxies

Nevalainen¹,

Eckert

Kaastra

et al. 2009

A&A

View full text Add to dashboard Cite

show abstract

“…Such emission may be of non-thermal origin, for example, Compton scattering of relativistic electrons by the cosmic microwave background radiation (see e.g. Rephaeli et al 2008;Petrosian et al 2008, and references therein for recent reviews), but alternative explanations have been put forward (Profumo 2008;Pérez-Torres et al 2009;Colafrancesco & Marchegiani 2009). Figure 8 shows the ROSAT HRI X-ray image of the cluster overlaid on the NVSS image.…”

Section: Ophiuchusmentioning

confidence: 99%

Rotation measures of radio sources in hot galaxy clusters

Govoni

Dolag

Murgia

et al. 2010

A&A

View full text Add to dashboard Cite

Aims. The goal of this work is to investigate the Faraday rotation measure (RM) of radio galaxies in hot galaxy clusters in order to establish a possible connection between the magnetic field strength and the gas temperature of the intracluster medium. Methods. We performed Very Large Array observations at 3.6 cm and 6 cm of two radio galaxies located in A401 and Ophiuchus, a radio galaxy in A2142, and a radio galaxy located in the background of A2065. All these galaxy clusters are characterized by high temperatures. Results. We obtained detailed RM images at an angular resolution of 3 for most of the observed radio galaxies. The RM images are patchy and reveal fine substructures of a few kpc in size. Under the assumption that the radio galaxies themselves have no effect on the measured RMs, these structures indicate that the intracluster magnetic fields fluctuate down to such small scales. These new data are compared with RM information present in the literature for cooler galaxy clusters. For a fixed projected distance from the cluster center, clusters with higher temperature show a higher dispersion of the RM distributions (σ RM ), mostly because of the higher gas density in these clusters. Although the previously known relation between the clusters X-ray surface brightness (S X ) at the radio galaxy location and σ RM is confirmed, a possible connection between the σ RM − S X relation and the cluster temperature, if present, is very weak. Therefore, in view of the current data, it is impossible to establish a strict link between the magnetic field strength and the gas temperature of the intracluster medium.

show abstract

“…This emission may be of non-thermal origin, caused presumably by Compton scattering of cosmic microwave background radiation by the relativistic electrons responsible for the mini-halo emission (see e.g., Rephaeli et al 2008;Petrosian et al 2008, and references therein for reviews). Alternative explanations have also been put forward (Profumo 2008;Pérez-Torres et al 2009;Colafrancesco & Marchegiani 2009). The HXR excess detection in Ophiuchus was recently confirmed by Nevalainen et al (2009).…”

Section: Introductionmentioning

confidence: 99%

GMRT observations of the Ophiuchus galaxy cluster

Murgia¹,

Eckert

Govoni³

et al. 2010

A&A

View full text Add to dashboard Cite

Aims. Observations with the Very Large Array telescope at 1477 MHz revealed the presence of a radio mini-halo surrounding the faint central point-like radio source in the Ophiuchus cluster of galaxies. In this work we present a study of the radio emission from this cluster of galaxies at lower radio frequencies. Methods. We observed the Ophiuchus cluster at 153, 240, and 614 MHz with the Giant Metrewave Radio Telescope. Results. The mini-halo is clearly detected at 153 and 240 MHz, the frequencies at which we reached the best sensitivity to the lowsurface brightness diffuse emission, while it is not detected at 610 MHz because of the too low signal-to-noise ratio at this frequency. The most prominent feature at low frequencies is a patch of diffuse steep spectrum emission located at about 5 south-east from the cluster centre. By combining these images with that at 1477 MHz, we derived the spectral index of the mini-halo. Globally, the minihalo has a low-frequency spectral index of α 153 240 1.4 ± 0.3 and an high-frequency spectral index of α 240 1477 1.60 ± 0.05. Moreover, we measure a systematic increase of the high-frequency spectral index with radius: the azimuthal radial average of α 240 1477 increases from about 1.3, at the cluster centre, up to about 2.0 in the mini-halo outskirts. Conclusions. The observed radio spectral index agrees with that obtained by modelling the non-thermal hard X-ray emission in this cluster of galaxies. We assume that the X-ray component arises from inverse-Compton scattering between the photons of the cosmic microwave background and a population of non-thermal electrons, which are isotropically distributed and whose energy spectrum is a power law with an index p. We derive that the electrons energy spectrum should extend from a minimum Lorentz factor of γ min 700 up to a maximum Lorentz factor of γ max 3.8 × 10 4 with an index p = 3.8 ± 0.4. The volume-averaged strength for a completely disordered intra-cluster magnetic field is B V 0.3 ± 0.1 μG.

show abstract

On the inverse Compton scattering interpretation of the hard X-ray excesses in galaxy clusters: the case of Ophiuchus

Cited by 21 publications

References 38 publications

XMM-Newton and INTEGRAL analysis of the Ophiuchus cluster of galaxies

XMM-Newton and INTEGRAL analysis of the Ophiuchus cluster of galaxies

Rotation measures of radio sources in hot galaxy clusters

GMRT observations of the Ophiuchus galaxy cluster

Contact Info

Product

Resources

About