  We present X-ray results on the ultraluminous infrared galaxy Arp220 obtained
with BeppoSAX. The X-ray emission up to 10 keV is detected. No significant
signal is detected with the PDS detector in the higher energy band. The 2-10
keV emission has a hard spectrum (photon-index of 1.7), similar to M82, and a
luminosity of 1e41 erg/s. A population of X-ray binaries may be a major source
of this X-ray emission. The upper limit of an iron K line equivalent width at
6.4 keV is ~600 eV. This observation imposes so far the tightest constraint on
an active nucleus if present in Arp220. We find that a column density of X-ray
absorption must exceed 10**25 cm-2 for an obscured active nucleus to be
significant in the energetics, and the covering factor of the absorption should
be almost unity. The underluminous soft X-ray starburst emission may need a
good explanation, if the bolometric luminosity is primarily powered by a
starburst.
