The X-ray structure of A399 and A401: A pre-merging cluster pair

We present ASCA results of the pair clusters A399 and A401. The region between the two clusters exhibits excess X-rays over the value expected with a simple superposition of the two clusters. We have found, however, no temperature rise at the merging front; the temperature is near the average of those in the inner regions of the two clusters. These facts indicate that although the two clusters are really interacting, it is not presently strong. The inner regions of the two clusters show no radial variations in the temperature, abundance or absorption. We set upper-limits of the mass-deposition rate of cooling how to be M < 35 M.yr(-1) and M < 59 M.yr(-1) for A399 and A401, respectively. A hint of an azimuthal variation in the temperature was also found.