NEXUS: Transient Searches and First Results from Year One Observations

We describe ongoing efforts of high-redshift transient searches using multi-epoch NIRCam imaging (F200W+F444W) and NIRSpec MSA/PRISM spectroscopy from the NEXUS JWST multi-cycle Treasury program targeting the north ecliptic pole region. The transient search area covers about 61.5, arcmin squared between the reference epoch and each subsequent NEXUS-Deep epoch at a cadence of about2 months. In the first year of observations from NEXUS, we detect 68 robust transients, with the host photometric redshift distribution declining rapidly at z>2 but extending to z phot about 6. In addition, we obtained secure spectroscopic redshifts for 37 transients (about54%) from NIRSpec/PRISM and NIRCam/WFSS, with seventeen at 1 < z < 2, eight at 2 < z < 3, two at 3 < z < 4, and one tentative host association at z = 6.151. Overall, the NEXUS program recovers observed supernova (SN) rates broadly consistent with other SN search programs with JWST. While NEXUS achieves the highest transient detection efficiency, 6.6 SNe per imaging hr (2.6 times COSMOS-SN and 26 times JADES-SN), the limited filter coverage (F200W+F444W only) limits robust identification and classification of high- z SNe for deep spectroscopic follow-up. We describe the details of the data reduction and transient detection pipeline, and report the Year-1 transient sample along with their light curves, available MSA spectroscopy, host association, and the raw detection rate. We also describe and release a new PSF photometry package that properly accounts for correlated pixel noise from combining drizzled images.