GALAXY CLUSTERS IN THE<i>SWIFT</i>/BURST ALERT TELESCOPE ERA: HARD X-RAYS IN THE INTRACLUSTER MEDIUM

Ajello, M.; Rebusco, P.; Cappelluti, N.; Reimer, O.; Böhringer, H.; Greiner, J.; Gehrels, N.; Tueller, J.; Moretti, A.

doi:10.1088/0004-637x/690/1/367

Cited by 101 publications

(144 citation statements)

References 158 publications

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“…The HXR excess detection in Ophiuchus was recently confirmed by Nevalainen et al (2009). In addition, their joint INTEGRAL and XMM analysis partly reconciled the previous discrepancy between the results by Eckert et al (2008) and the upper limits on HXR flux obtained by Ajello et al (2009) through Swift/BAT data.…”

Section: Introductionmentioning

confidence: 55%

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GMRT observations of the Ophiuchus galaxy cluster

Murgia¹,

Eckert

Govoni³

et al. 2010

A&A

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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.

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Section: Introductionmentioning

confidence: 55%

“…8). We also added to the SED the upper limits at 74 MHz (VLSS) and 607 MHz (GMRT), as well as the Swift upper limit (Ajello et al 2009). …”

Section: Discussionmentioning

confidence: 99%

GMRT observations of the Ophiuchus galaxy cluster

Murgia¹,

Eckert

Govoni³

et al. 2010

A&A

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“…Extended (several arcminutes in scale) hard X-ray emission (with so far weak evidence for a non-thermal component) has been observed (Rephaeli & Gruber 2002;Fusco-Feminano et al 2004;Rossetti et al 2004;Lutovinov et al 2008;Ajello et al 2009), as well as a prominent non-thermal radio halo (Giovannini et al 1993;Thierbach et al 2003). The latter is clear evidence for particle acceleration.…”

Section: Introductionmentioning

confidence: 96%

Constraints on the multi-TeV particle population in the Coma galaxy cluster with HESS observations

Aharonian

Akhperjanian

Anton

et al. 2009

A&A

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Aims. Galaxy clusters are key targets in the search for ultra high energy particle accelerators. The Coma cluster represents one of the best candidates for such a search owing to its high mass, proximity, and the established non-thermal radio emission centred on the cluster core. Methods. The HESS (High Energy Stereoscopic System) telescopes observed Coma for ∼8 h in a search for γ-ray emission at energies >1 TeV. The large 3.5 • FWHM field of view of HESS is ideal for viewing a range of targets at various sizes including the Coma cluster core, the radio-relic (1253+275) and merger/infall (NGC 4839) regions to the southwest, and features greater than 1 • away. Results. No evidence for point-like nor extended TeV γ-ray emission was found and upper limits to the TeV flux F(E) for E > 1, >5, and >10 TeV were set for the Coma core and other regions. Converting these limits to an energy flux E 2 F(E) the lowest or most constraining is the E > 5 TeV upper limit for the Coma core (0.2 • radius) at ∼8% Crab flux units or ∼10 −13 ph cm −2 s −1 . Conclusions. The upper limits for the Coma core were compared with a prediction for the γ-ray emission from proton-proton interactions, the level of which ultimately scales with the mass of the Coma cluster. A direct constraint using our most stringent limit for E > 5 TeV, on the total energy content in non-thermal protons with injection energy spectrum ∝E −2.1 and spatial distribution following the thermal gas in the cluster, is found to be ∼0.2 times the thermal energy, or ∼10 62 erg. The E > 5 TeV γ-ray threshold in this case corresponds to cosmic-ray proton energies > ∼ 50 TeV. Our upper limits rule out the most optimistic theoretical models for gamma ray emission from clusters and complement radio observations which constrain the cosmic ray content in clusters at significantly lower proton energies, subject to assumptions on the magnetic field strength.

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“…Analyzing INTEGRAL, ROSAT, and RXTE data, Lutovinov et al (2008) found that the global Coma spectrum is well fitted with a thermal model and the evidence for a hard excess is very marginal (1.6σ ). Ajello et al (2009) analyzed combined XMM-Newton and hard X-ray Swift-BAT spectra and even though they could not rule out the presence of non-thermal hard X-ray emission outside of their 10 region, within their field of view they found a good fit with two thermal models, with no need for a non-thermal component. Wik et al (2009) analyzed combined Suzaku Hard X-ray Detector (HXD-PIN) and XMMNewton mosaic spectra of a larger 34 × 34 region centered on the Coma cluster.…”

Section: Shocks and Non-equilibriummentioning

confidence: 97%

X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories

Böhringer

Werner

2009

Astron Astrophys Rev

194

142

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Galaxy clusters, the largest clearly defined objects in our Universe, are ideal laboratories to study in detail the cosmic evolution of the intergalactic intracluster medium (ICM) and the cluster galaxy population. For the ICM, which is heated to X-ray radiating temperatures, X-ray spectroscopy is the most important tool to obtain insight into the structure and astrophysics of galaxy clusters. The ICM is also the hottest plasma that can be well studied under thermal equilibrium conditions. In this review we recall the basic principles of the interpretation of X-ray spectra from a hot, tenuous plasma and we illustrate the wide range of scientific applications of X-ray spectroscopy. The determination of galaxy cluster masses, the most important prerequisite for using clusters in cosmological studies, rest crucially on a precise spectroscopic determination of the ICM temperature distribution. The study of the thermal structure of the ICM provides a very interesting fossil record of the energy release during galaxy formation and evolution, giving important constraints on galaxy formation models. The temperature and pressure distribution of the ICM gives us important insight into the process of galaxy cluster merging and the dissipation of the merger energy in form of turbulent motion. Cooling cores in the centers of about half of the cluster population are interesting laboratories to investigate the interplay between gas cooling, star-and black hole formation and energy feedback, which is diagnosed by means of X-ray spectroscopy. The element abundances deduced from X-ray spectra of the ICM provide a cosmic history record of the contribution of different supernovae to the nucleosynthesis of heavy elements and their spatial distribution partly reflects important transport processes in the ICM. Some discussion of plasma diagnostics for conditions out of thermal equilibrium and an outlook on the future prospects of X-ray spectroscopic cluster studies complete our review.

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GALAXY CLUSTERS IN THESWIFT/BURST ALERT TELESCOPE ERA: HARD X-RAYS IN THE INTRACLUSTER MEDIUM

Cited by 101 publications

References 158 publications

GMRT observations of the Ophiuchus galaxy cluster

GMRT observations of the Ophiuchus galaxy cluster

Constraints on the multi-TeV particle population in the Coma galaxy cluster with HESS observations

X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories

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