  Aims. We study the long-term variability of the well-known Seyfert 2 galaxy
Mrk 1210 (a.k.a. UGC 4203, or the Phoenix galaxy).
  Methods. The source was observed by many X-ray facilities in the last 20
years. Here we present a NuSTAR observation and put the results in context of
previously published observations.
  Results. NuSTAR observed Mrk 1210 in 2012 for 15.4 ks. The source showed
Compton-thin obscuration similar to that observed by Chandra, Suzaku, BeppoSAX
and XMM-Newton over the past two decades, but different from the first
observation by ASCA in 1995, in which the active nucleus was caught in a low
flux state - or obscured by Compton-thick matter, with a reflection-dominated
spectrum. Thanks to the high-quality hard X-ray spectrum obtained with NuSTAR
and exploiting the long-term spectral coverage spanning 16.9 years, we can
precisely disentangle the transmission and reflection components and put
constraints on both the intrinsic long-term variability and hidden nucleus
scenarios. In the former case, the distance between the reflector and the
source must be at least ~ 2 pc, while in the latter one the eclipsing cloud may
be identified with a water maser-emitting clump.
