NuSTAR view of the central region of M 31
  Our neighbouring large spiral galaxy, the Andromeda galaxy (M 31 or NGC 224),
is an ideal target to study the X-ray source population of a nearby galaxy.
NuSTAR observed the central region of M 31 in 2015 and allows studying the
population of X-ray point sources at energies higher than 10 keV. Based on the
source catalogue of the large XMM-Newton survey of M 31, we identified
counterparts to the XMM-Newton sources in the NuSTAR data. The NuSTAR data only
contain sources of a brightness comparable (or even brighter) than the selected
sources that have been detected in XMM-Newton data. We investigate hardness
ratios, spectra and long-term light curves of individual sources obtained from
NuSTAR data. Based on our spectral studies we suggest four sources as possible
X-ray binary candidates. The long-term light curves of seven sources that have
been observed more than once show low (but significant) variability.
