A Focused, Hard X-ray Look at Arp 299 with NuSTAR
  We report on simultaneous observations of the local starburst system Arp 299
with NuSTAR and Chandra, which provides the first resolved images of this
galaxy up to energies of ~ 45 keV. Fitting the 3-40 keV spectrum reveals a
column density of $N_{\rm H}$ ~ 4 x10^{24} cm^{-2}, characteristic of a
Compton-thick AGN, and a 10-30 keV luminosity of 1.2x 10^{43} ergs s^{-1}. The
hard X-rays detected by NuSTAR above 10 keV are centered on the western
nucleus, Arp 299-B, which previous X-ray observations have shown to be the
primary source of neutral Fe-K emission. Other X-ray sources, including Arp
299-A, the eastern nucleus which is also thought to harbor an AGN, as well as
X-ray binaries, contribute $\lesssim 10%$ to the 10-20 keV emission from the
Arp 299 system. The lack of significant emission above 10 keV other than that
attributed to Arp 299-B suggests that: a) any AGN in Arp 299-A must be heavily
obscured ($N_{\rm H}$ > 10^{24} cm^{-2}) or have a much lower luminosity than
Arp 299-B and b) the extranuclear X-ray binaries have spectra that cut-off
above ~10 keV. Such soft spectra are characteristic of ultraluminous X-ray
(ULX) sources observed to date by NuSTAR.
