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Two recent observations of the nearby galaxy NGC 6946 with NuSTAR, onesimultaneous with an XMM-Newton observation, provide an opportunity to examineits population of bright accreting sources from a broadband perspective. Westudy the three known ultraluminous X-ray sources (ULXs) in the galaxy, andfind that ULX-1 and ULX-2 have very steep power-law spectra with$\Gamma=3.6^{+0.4}_{-0.3}$ in both cases. Their properties are consistent withbeing super-Eddington accreting sources with the majority of their hardemission obscured and down-scattered. ULX-3 (NGC 6946 X-1) is significantlydetected by both XMM-Newton and NuSTAR at $L_{\rm X}=(6.5\pm0.1)\times10^{39}$erg s$^{-1}$, and has a power-law spectrum with $\Gamma=2.51\pm0.05$. We areunable to identify a high-energy break in its spectrum like that found in otherULXs, but the soft spectrum likely hinders our ability to detect one. We alsocharacterise the new source, ULX-4, which is only detected in the jointXMM-Newton and NuSTAR observation, at $L_{\rm X}=(2.27\pm0.07)\times10^{39}$erg s$^{-1}$, and is absent in a Chandra observation ten days later. It has avery hard cut-off power-law spectrum with $\Gamma=0.7\pm0.1$ and $E_{\rmcut}=11^{+9}_{-4}$ keV. We do not detect pulsations from ULX-4, but itstransient nature can be explained either as a neutron star ULX briefly leavingthe propeller regime or as a micro-tidal disruption event induced by astellar-mass compact object.

A broadband look at the old and new ULXs of NGC 6946