We present X-ray observations of the northern outskirts of the relaxed galaxy cluster A1413 with Suzaku, whose XIS instrument has the low intrinsic background needed to make measurements of these low surface brightness regions. We excise 15 point sources superimposed on the image above a flux of 1 × 10 −14 erg cm −2 s −1 (2-10 keV) using XMM-Newton and Suzaku images of the cluster. We quantify all known systematic errors as part of our analysis, and show our statistical errors encompasses them for the most part. Our results extend previous measurements with Chandra 1 and XMM-Newton, and show a significant temperature drop to about 3 keV at the virial radius, r 200 . Our entropy profile in the outer region (> 0.5 r 200 ) joins smoothly onto that of XMM-Newton, and shows a flatter slope compared with simple models, similar to a few other clusters observed at the virial radius. The integrated mass of the cluster at the virial radius is approximately 7.5 × 10 14 M ⊙ and varies by about 30% depending on the particular method used to measure it.

We observed outer regions of a bright cluster of galaxies A2142 with Suzaku. Temperature and brightness structures were measured out to the virial radius (r 200 ) with good sensitivity. We confirmed the temperature drop from 9 keV around the cluster center to about 3.5 keV at r 200 , with the density profile well approximated by the β model with β = 0.85. Within 0.4 r 200 , the entropy profile agrees with r 1.1 , as predicted by the accretion shock model. The entropy slope becomes flatter in the outer region and negative around r 200 . These features suggest that the intracluster medium in the outer region is out of thermal equilibrium. Since the relaxation timescale of electron-ion Coulomb collision is expected to be longer than the elapsed time after shock heating at r 200 , one plausible reason of the low entropy is the low electron temperature compared to that of ions. Other possible explanations would be gas clumpiness, turbulence and bulk motions of ICM. We also searched for a warm-hot intergalactic medium around r 200 and set an upper limit on the oxygen line intensity. Assuming a line-of-sight depth of 2 Mpc and oxygen abundance of 0.1 solar, the upper limit of an overdensity is calculated to be 280 or 380, depending on the foreground assumption.

High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified » E 3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S XVI (  E 3.44 keV rest-frame)-a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

Context. Measurements of intracluster gas temperatures out to large radii, where much of the galaxy cluster mass resides, are important for using clusters for precision cosmology and for studies of cluster physics. Previous attempts to measure robust temperatures at cluster virial radii have failed. Aims. The goal of this work is to measure the temperature profile of the very relaxed symmetric galaxy cluster Abell 2204 out to large radii, possibly reaching the virial radius. Methods. Taking advantage of its low particle background due to its low-Earth orbit, Suzaku data are used to measure the outer temperature profile of Abell 2204. These data are combined with Chandra and XMM-Newton data of the same cluster to make the connection to the inner regions, unresolved by Suzaku, and to determine the smearing due to Suzaku's point spread function. Results. The temperature profile of Abell 2204 is determined from ∼10 kpc to ∼1800 kpc, close to an estimate of r 200 (the approximation to the virial radius). The temperature rises steeply from below 4 keV in the very center up to more than 8 keV in the intermediate range and then decreases again to about 4 keV at the largest radii. Varying the measured particle background normalization artificially by ±10% does not change the results significantly. Several additional systematic effects are quantified, e.g., those due to the point spread function and astrophysical fore-and backgrounds. Predictions for outer temperature profiles based on hydrodynamic simulations show good agreement. In particular, we find the observed temperature profile to be slightly steeper but consistent with a drop of a factor of 0.6 from 0.3 r 200 to r 200 , as predicted by simulations. Conclusions. Intracluster gas temperature measurements up to r 200 seem feasible with Suzaku, after a careful analysis of the different background components and the effects of the point spread function. Such measurements now need to be performed for a statistical sample of clusters. The result obtained here indicates that numerical simulations capture the intracluster gas physics well in cluster outskirts.

We present results from the XMM-Newton observation of the non-cooling flow cluster A 1060. Large effective area of XMM-Newton enables us to investigate the nature of this cluster in unprecedented detail. From the observed surface brightness distribution, we have found that the gravitational mass distribution is well described by the NFW profile but with a central density slope of ∼1.5. We have undoubtedly detected a radial temperature decrease of as large as ∼30% from the center to the outer region (r ∼ 13 ′ ), which seems much larger than that expected from the temperature profile averaged over nearby clusters. We have established that the temperature of the region ∼ 7 ′ southeast of the center is higher than the azimuthally averaged temperature of the same radius by ∼20%. Since the pressure of this region already reaches equilibrium with the environment, the temperature structure can be interpreted as having been produced between 4×10 7 yr (the sound-crossing time) and 3×10 8 yr (the thermal conduction time) ago. We have found that the high-metallicity blob located at ∼ 1. ′ 5 northeast of NGC 3311 is more extended and its iron mass of 1.9 × 10 7 M ⊙ is larger by an order of magnitude than estimated from our Chandra observation. The amount of iron can still be considered as being injected solely from the elliptical galaxy NGC 3311.