Spartan 1 X-ray observations of the perseus cluster. II. The distribution of flux and hardness ratio out to a radius of 50 arcminutes

The 1-10 keV X-ray observations of the Perseus Cluster by Spartan 1 have yielded a map of the X-ray emission and the distribution of X-ray hardness ratio with radius from the cluster center. The surface brightness contours are approximately circular within 10′ of the center, but outside this radius become increasingly elongated so that the major axis/minor axis ratio reaches 1.2 beyond 20′. The position angle of the major axis is about 84° east of north within 20′, consistent with optical results, but may shift to approximately 70° at larger radii. The centroid of the X-ray emission lies 2′.4 east of NGC 1275. Also, at radii greater than 20′ in the southwest, coincident with the line of bright galaxies between NGC 1275 and IC 310, there is an enhancement in the X-ray surface brightness. These asymmetries may be evidence that outside 10′ (≃300kpc) the cluster has not reached dynamic equilibrium. Using a spherically symmetric model we find that the intracluster gas is approximately isothermal between radii of 10′ and 50′, consistent with a temperature of 7.5 ± 0.5 × 10⁷ K. Ninety percent confidence limits of 0.85-1.14 have been established for the corresponding polytropic exponent. The two-dimensional distribution of hardness ratio suggests that at radii greater than about 25′ (800 kpc), the gas temperature is lower east of NGC 1275 than in other directions.