A Dusty X‐Ray Absorber in the Perseus Cluster?

We have analyzed 0.35-7.5 keV X-ray spectra of the center of the Perseuscluster collected using the Broad Band X-Ray Telescope (BBXRT) on the Astro-1mission. These spectra are particularly useful for examining the nature of theX-ray absorber in cooling flows because of BBXRT's sensitivity between 0.35 and1.0 keV. We confirm that there is X-ray absorption above that expected from gasin our own galaxy. Further, the absorbing medium is deficient in helium.However, the energy of the K-edge of oxygen is consistent with neutral material(at the redshift of the cluster) and is not consistent with any ionized stateof oxygen. It is not possible to completely ionize helium and have oxygenneutral so the apparent helium deficiency cannot be due to ionization. Wepropose that the X-ray absorption is due to dust grains that have condensed outof a medium in which helium remains ionized. This model satisfies all theobservational constraints but is difficult to understand theoretically.Comment: 15 pages including 6 figures. Uses aaspp4 and psfig style