Hard X-ray Emission from the Arches Cluster Region Observed with NuSTAR

The Arches cluster is a young, densely packed massive star cluster in our Galaxy, showing high level of star formation activity. The X-ray emission from the cluster is a mix of thermal and nonthermal radiation. The thermal emission is thought to arise from collisions between the strong winds of massive stars. The nonthermal diffuse emission prominent in the iron K_alpha line emission at 6.4 keV, detected in the broad area around the cluster, may be produced by the interaction of low-energy cosmic-ray electrons and ions with neutral ambient gas. The diffuse 6.4 keV fluorescent line emission may be also the result of the irradiation of cold matter by hard X-rays photons. Previously, the lack of spectral measurements above 10 keV did not allow for a definitive conclusion about the ionizing mechanism. Thanks to the recently launched NuSTAR mission, we performed the first imaging and spectral measurements of the Arches cluster at energies above 10 keV. Preliminary analysis of the NuSTAR data shows that hard X-ray emission is extended in the broad region around the cluster where the 6.4 keV iron line is observed. The details of the analysis and possible interpretation will be discussed in this presentation.