Confirmation of the Presence of Nonthermal Hard X-Ray Excess in the Cluster A2256 from Two Epoch Observations

After confirmation of the presence of a nonthermal hard X-ray excess with respect to the thermal emission in the Coma Cluster from two independent observations, obtained using the Phoswich Detection System on board BeppoSAX , we also present in this Letter the results of two observations of A2256 performed with a time interval of about 2.5 yr. In both spectra a nonthermal excess is present at a confidence level of ~3.3 σ and ~3.7 σ, respectively. The combined spectrum obtained by adding up the two spectra allows us to measure an excess at the level of ~4.8 σ in the 20-80 keV energy range. The nonthermal X-ray flux is in agreement with the published value of the first observation (Fusco-Femiano et al.) and with that measured by a Rossi X-Ray Timing Explorer observation (Rephaeli & Gruber).