The NuSTAR and XMM extragalactic survey of the James Webb Space Telescope North Ecliptic Pole time-domain field

We present the NuSTAR and XMM surveys of the James Webb Space Telescope (JWST) Time-Domain Field (TDF) near the North Ecliptic Pole (NEP). The JWST NEP is a GTO target allocated ~47 JWST hours. JWST will visit the NEP TDF four times, every 90 days after the first observation taken in Aug. 2022. A deep multi-wavelength campaign using ground and space-based observatories covering from radio to hard X-rays is in progress. The NuSTAR survey of JWST NEP TDF is the deepest NuSTAR extragalactic survey performed to date with a total exposure of 1.5 Ms (Cycle 5 and Cycle 6, multi-year program) which covers 0.16 square degrees. In this field, we have detected ~60 NuSTAR sources, including variable and transient sources appearing only in single observations. We present the X-ray and multiwavelength properties of the detected sources, including the XMM counterparts. As this survey was designed to have variability as its primary focus, we report the first study of multi-year variability in NuSTAR surveys, thanks to our multi-epochal monitoring in the NuSTAR-NEP field, using an innovative method to analyze hard X-ray variability recently developed by our group. The brightest X-ray source in the field is a flat spectrum radio quasar (FSRQ; z=1.44); we report its multi-year X-ray spectral variability utilizing also the high-quality Chandra and XMM observations. We also present its optical light curve, which exhibits a different trend from X-rays, as well as the SED analysis of this source. Four more NuSTAR and XMM observations were granted in Cycle 8 to observe the field simultaneously with JWST and this program is in progress. Four NuSTAR sources and fifteen XMM sources were covered by the first JWST TDF observation, where two out of the four NuSTAR detected sources are Compton-thick AGN candidates.