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We report hints for the correlation between the X-ray and gamma-ray emissionin the nearby galaxy NGC 4945, which harbors both an active galactic nucleusand a nuclear starburst region. We have divided the Fermi/LAT observations ofNGC 4945 into two datasets, comprising events detected during the low (L) andhigh (H) level of X-ray emission from the active nucleus of this galaxy,determined using the Swift/BAT light curve. Both datasets contain an equalamount of 3.8 years of LAT data and NGC 4945 is detected with a similarstatistical significance of ~15 $\sigma$ in L and 14 $\sigma$ in H. However,the slope of the gamma-ray spectrum hardens with the increase of the X-rayflux, with the photon index $\Gamma$ = 2.47 +/- 0.07 in L and 2.11 +/- 0.08 inH. The change is confirmed by a systematic variation of the spectral energydistribution as well as a substantial reversal of the gamma-ray signal insignificance maps for low and high gamma-ray energies. The X/gamma-raycorrelation indicates that the gamma-ray production is dominated by the activenucleus rather than by cosmic rays interacting with the interstellar medium. Wediscuss possible locations of the gamma-ray source. We also compare NGC 4945with other starburst galaxies detected by LAT and we note similarities betweenthose with active nuclei, e.g. unlikely high efficiencies of gamma-rayproduction in starburst scenario, which argues for a significant contributionof their active nuclei to the gamma-ray emission.

The X/gamma-ray correlation in NGC 4945 and the nature of its gamma-ray source