The recent NuSTAR observing schedule has been dominated by Target of Opportunity observations and coordinated observations with other high energy observatories. Among the time-constrained observations, several were scheduled to study precise moments in the orbital phases of binary systems. These include an observation of AXJ1700.2-4220, a recently rediscovered X-ray pulsator found while searching the HEASARC archive of X-ray data. Most systems discovered in this way are likely white dwarf binary systems, but the archival data for AXJ1700.2-4220 suggest the presence of an accreting neutron star in a rare binary system. With the goal of unambiguously assessing the nature of this unusual system, NuSTAR observed the source during the orbital phase when pulsations were expected to be strongest. NuSTAR has also obtained multiple observations of the gamma-ray binary system LS I +61 303 to sample key phases across its 26.5-day orbit. The NuSTAR observations were originally planned for later this year, but an independent campaign of observations with the Nordic Optical Telescope, timed to be performed around the expected peak of X-ray flaring activity, persuaded the NuSTAR Science Operations Center to bring forward those observations. The NuSTAR and multi-observatory data from these observing campaigns, which include a Director's Discretionary Time observation by ESA's XMM-Newton observatory, will be part of a collaboration between multiple teams of researchers.
Author: Karl Forster (NuSTAR Science Operations Manager, Caltech)
