ASCA Observation of the Poor Cluster of Galaxies AWM 7: Evidence of an Abundance Increase in the Intra-Cluster Medium at the Center

We present the results of the ASCA central-pointing observation of the poor cD cluster AWM 7. The Performance Verification phase data of GIS 2, GIS 3, SIS 0 chip 1, and SIS 1 chip 3 were used to study the properties of the intra-cluster medium (ICM) within 16′ around the X-ray centroid. We found that, compared with the outer regions, the equivalent width of the Fe-K lines increases in the central 4′ (∼ 123 h−150 kpc) region by a factor of ∼ 1.5. Although the ICM temperature tends to decrease in the same region, the observed increase in the Fe-K line equivalent width cannot be explained away by a possible temperature drop. The model fitting indicates that the abundance increases from ∼ 0.4 solar outside 4′ to ∼ 0.6 solar at the center. Thus, after the Centaurus cluster and the Virgo cluster, AWM 7 is the third poor cD cluster confirmed to show an abundance increase in the central region. The 0.5−3 keV flux of the cool emission within 4′ is constrained to be < 8 × 1042)h−250 erg s−1, or < 21% of the total 0.5–3 keV flux from the same spatial region. We discuss possible relations of these phenomena to the cD galaxy.