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DETECTION OF EMISSION FROM WARM-HOT GAS IN THE UNIVERSE WITH XMM?
BOWYER STUART,VIKHLININ ALEXEY The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5
Recently, claims have been made of the detection of 'warm-hot' gas in the intergalactic medium. Kaastra et al. (2003) claimed detection of ${\~} 10^6$ K material in the Coma Cluster but studies by Arnaud et al. (2001), and our analysis of the Chandra observations of Coma (Vikhlinin et al. 2001), find no evidence for a $10^6$ K gas in the cluster. Finoguenov et al. (2003) claimed the detection of $3 {\times} 10^6$ gas slightly off-center from the Coma Cluster. However, our analysis of ROSAT data from this region shows no excess in this region. We propose an alternative explanation which resolves all these conflicting reports. A number of studies (e.g. Robertson et al., 2001) have shown that the local interstellar medium undergoes charge exchange with the solar wind. The resulting recombination spectrum shows lines of O VII and O VIII (Wargelin et al. 2004). Robertson & Cravens (2003) have .shown that as much as $25\%$ of the Galactic polar flux is heliospheric recombination radiation and that this component is highly variable. Sporadic heliospheric emission could account for all the claims of detections of 'warm-hot' gas and explain the conflicts cited above.
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EUV AND SOFT X-RAY EMISSION IN CLUSTERS OF GALAXIES
STUART BOWYER 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5
Observations with EUVE, ROSAT, and BeepoSAX have shown that some clusters of galaxies produceintense EUV emission. These ndings have produced considerable interest; over 100 papers have beenpublished on this topic in the refereed literature. A notable suggestion as to the source of this radiationis that it is a \warm" (106 K) intracluster medium which, if present, would constitute the major baryoniccomponent of the universe. A more recent variation of this theme is that this material is \warm-hot"intergalactic material condensing onto clusters. Alternatively, inverse Compton scattering of low energycosmic rays against cosmic microwave background photons has been proposed as the source of thisemission. Various origins of these particles have been posited, including an old ( Giga year) populationof cluster cosmic rays; particles associated with relativistic jets in the cluster; and cascading particlesproduced by shocks from sub-cluster merging. The observational situation has been quite uncertainwith many reports of detections which have been subsequently contradicted by analyses carried out byother groups. Evidence supporting a thermal and a non-thermal origin has been reported. The existingEUV, FUV, and optical data will be briey reviewed and claried. Direct observational evidence froma number of dierent satellites now rules out a thermal origin for this radiation. A new examination ofsubtle details of the EUV data suggests a new source mechanism: inverse Compton scattered emissionfrom secondary electrons in the cluster. This suggestion will be discussed in the context of the data.
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KUO PING-HUNG,BOWYER STUART,HWANG CHORNG- YUAN The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5
A substantial number of processes have been suggested as possible contributors to the extragalactic $\gamma$-ray background (EGRB). Yet another contribution to this background will be emission produced in hadronic interactions of cosmic-ray protons with the cluster thermal gas; this class of cosmic rays (CRs) has been shown to be responsible for the EUV emission in the Coma Cluster of galaxies. In this paper we assume the CRs in the Coma Cluster is prototypic of all clusters and derive the contribution to the EGRB from all clusters over time. We examine two different possibilities for the scaling of the CR flux with cluster size: the number density of the CRs scale with the number density of the thermal plasma, and alternatively, the energy density of the CRs scale with the energy density of the plasma. We find that in all scenarios the EGRB produced by this process is sufficiently low that it will not be observable in comparison with other mechanisms that are likely to produce an EGRB.
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