A couple of weeks ago, the annual International Astronomical Consortium for High-Energy Calibration workshop was held in Osaka, Japan, and was attended by several members of the NuSTAR calibration team. The purpose of this workshop is for various high-energy astronomy missions to compare their measurements of targets in common to ensure that their instruments are sufficiently well-calibrated to reach agreement, as well as to discuss relevant factors such as telescope performance and health over time, and suitable astronomical targets for calibration purposes. In particular, presentations this year have shown excellent agreement between NuSTAR and the NASA/JAXA mission XRISM instruments. Additionally, NuSTAR Project Scientist Hannah Earnshaw will be co-chairing a new working group related to science operations discussion.
 
A nearly two-day-long exposure of NGC 4051 was recently conducted using NuSTAR in coordination with XRISM. Further support was coordinated with ESA’s XMM-Newton mission that performed a long exposure overlapping with both, along with optical spectroscopic monitoring using the Seimei Telescope and a 4-orbit observation by NASA’s HST which will occur later in the year. The new calorimeter technology afforded by the Resolve instrument on XRISM will yield precise profile measurements of features in the Fe K band — emission from the element iron which is produced close to the event horizon of the black hole — and will allow unprecedented constraints on the nature of the matter which is reprocessing the high-energy emission, since the black hole mass in NGC 4051 is already tightly constrained. XRISM will determine the precise origin of the Fe K-alpha line, measure the kinematics of the ionized outflow matter, and detect and identify other unexplained X-ray line emission previously seen at lower energies. NuSTAR will be vital in constraining the shape of the continuum emission so that XRISM's measurements of the Fe K-alpha line are as accurate as possible.  This campaign will reveal reprocessing signatures over a broad range of ionization state, column density and kinematics — revealing contributions from the accretion disk, broad-line region, and material surrounding the black hole in a torus. Most importantly, the new X-ray data will allow us the first meaningful constraints that map the inner regions of the accretion disk.

Authors:  Hannah Earnshaw (NuSTAR Project Scientist, Caltech), Prof. Tracey Jane Turner (Eureka Scientific, Inc.)