A SEARCH FOR SMALL-SCALE X-RAY SURFACE BRIGHTNESS FLUCTUATIONS IN CLUSTERS OF GALAXIES

A search for small-scale structure in the X-ray surface brightness of 20 nearby (z ≤ 0.036) clusters of galaxies is described. Our technique is to compare 0.3-3.5 keV observations made with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory to detailed simulations of intrinsically smooth clusters. The simulations include modulations introduced by the IPC and background/foreground X-ray sources. Each cluster is divided into ∼four radial zones for analysis. We divide these radial zones into two subsamples (each containing 38 zones) on the basis of total detected IPC counts; we refer to these as the low-count and high-count samples. The rms fluctuations due to counting statistics alone are typically in the range of 10%-30% in the high-count sample. We detect excess fluctuations of 1′ scale in the high-count sample, but none in the low-count sample. The excess fluctuations in the high-count sample could be produced by ∼one source per zone emitting at ∼4 × 1041 ergs s-1 in soft X-rays. We suggest that low-luminosity active nuclei in the cluster galaxies or a hot interstellar medium retained by some galaxies are the most likely origins of this emission.