Suzaku observations of iron K-lines from the intracluster medium of the coma cluster

Abstract

The Coma cluster was observed with the X-ray Imaging Spectrometer (XIS) onboard Suzaku in six pointings, including the central X-ray peak region, 140 west offset region, 300 and 340 north-west offset regions, and 440 and 600 south-west offset regions. Owing to its lower background level, Suzaku has better sensitivity to Fe K? lines than other satellites. Using precise Fe line measurements, we studied the temperature structure, possible bulk motions, and iron abundance distributions in the intracluster medium (ICM). The observed spectra were well-represented by a single-temperature model; a two- or three- temperature model did not improve Χ2 substantially. The temperature, derived from Kα line ratios of H-like and He-like Fe, agrees with those derived from the single-temperature model. Because the line ratio is a steep function of temperature, the consistency supports the accuracy of temperature measurements conducted with Suzaku. Within the 340 region, the redshift derived from the central energy of the He-like Fe line is consistent with that from optical observations, within a calibration error of 18 eV or 818 kms-1 in the line of sight. This value is smaller than the sound velocity of the ICM, which is 1500km s-1. The central energy of Fe lines at the 440 offset region around the NGC 4839 subcluster is also consistent with those within the 340 region. These results on the temperature and velocity structure suggest that the core of the cluster is in a relaxed state, and non-thermal electrons relevant to the radio halo are accelerated by intracluster turbulence rather than large-scale shocks. The Fe abundance is almost constant at 0.4 solar within the 340 region, and decreases with radius. This value is slightly lower than those of other clusters, which means that the gas had been mixed well during a past merger associated with the growth of the cluster. © 2011. Astronomical Society of Japan.