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

Abstract

ABSTRACT We present the NuSTAR extragalactic survey of the James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field. The survey covers a ∼0.16 deg2 area with a total exposure of 681 ks acquired in a total of nine observations from three epochs. The survey sensitivities at 20 per cent of the area are 2.39, 1.14, 2.76, 1.52, and 5.20 × 10−14 erg cm−2 s−1 in the 3–24, 3–8, 8–24, 8–16, and 16–24 keV bands, respectively. The NEP survey is one of the most sensitive extragalactic surveys with NuSTAR so far. A total of 33 sources were detected above 95 per cent reliability in at least one of the five bands. We present the number counts, logN-logS, measured in the hard X-ray 8–24 and 8–16 keV bands, uniquely accessible by NuSTAR down to such faint fluxes. We performed source detection on the XMM–Newton and Chandra observations of the same field to search for soft X-ray counterparts of each NuSTAR detection. The soft band positions were used to identify optical and infrared associations. We present the X-ray properties (hardness ratio and luminosity) and optical-to-X-ray properties of the detected sources. The measured fraction of candidate Compton-thick (N$\rm _H\ge 10^{24}\, cm^{-2}$) active galactic nuclei, derived from the hardness ratio, is between 3 and 27 per cent. As this survey was designed to have variability as its primary focus, we present preliminary results on multiepoch flux variability in the 3–24 keV band.