NuSTAR is performing a series of observations this month coordinated with NASA’s Imaging X-ray Polarimetry Explorer (IXPE). Most targets observed by IXPE are also now observed by NuSTAR, either as part of joint observing proposals submitted to peer reviewed General Observer (GO) programs, or in response to requests from the community to provide short exposures to aid in scientific analysis of IXPE observations. NuSTAR’s broad range of timing and energy sensitivity can deliver precise constraints on the X-ray continuum shape and variability, complementary to the X-ray polarimetry measurements by IXPE. The observations this month have included symbiotic X-ray binaries and pulsars as well as target-of-opportunity observations of transient X-ray flares requiring quick scheduling responses of the NuSTAR and IXPE teams. A simultaneous observation of the Crab nebula was also performed last month, which is used as a calibration target for X-ray missions. Combined analysis of the NuSTAR and IXPE data will improve the detailed calibration of each mission. Multi-mission cross calibration has become an important aspect of investigations of astrophysical X-ray sources with the number of coordinated observations with NuSTAR and other X-ray observatories continuing to rise. This increase in the usefulness of joint observations was reflected in the doubling of the number of proposals requesting coordinated NuSTAR observations submitted to the IXPE GO cycle-3 program last month. The total NuSTAR observing time requested by the astrophysics community was more than five times that available for the joint program, which has become highly competitive. The selection of proposals for observations in IXPE cycle-3 is expected to be released before the end of the year, with observations beginning February 1st, 2026.
Authors: Karl Forster (NuSTAR Operations Lead, California Institute of Technology)
