Osse observations of the ultraluminous infrared galaxies ARP 220, Markarian 273, and Markarian 231

We report results of soft gamma-ray observations of the ultraluminous infrared galaxies Arp 220, Mrk 273, and Mrk 231 in order to test whether the infrared radiation from these sources originates from buried active galactic nuclei (AGNs). Only upper limits are measured, implying that the emergent soft gamma-ray luminosities are 1-2 orders of magnitude smaller than the infrared luminosities. Monte Carlo simulations of radiation transport through tori are used to infer the minimum column densities N-H required to block transmission of soft gamma-rays from a buried AGN, assuming that spectra of AGNs in such sources are similar to those of radio-quiet quasars. Lack of measured gamma-ray emission provides no supporting evidence for the existence of buried AGNs in these galaxies, but is consistent with an origin of the infrared luminosity from starburst activity.