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The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- I. Instrument Overview and in-Flight Performance Published: 6/6/2023 12:55:00 AM Updated: 6/6/2023 12:55:00 AM

Paper abstract: The Near-Infrared Imager and Slitless Spectrograph (NIRISS) is the sciencemodule of the Canadian-built Fine Guidance Sensor (FGS) onboard the James WebbSpace Telescope (JWST). NIRISS has four observing modes: 1) broadband imagingfeaturing seven of the eight NIRCam broadband filters, 2) wide-field slitlessspectroscopy (WFSS) at a resolving power of ~150 between 0.8 and 2.2\mum, 3) single-object cross-dispersed slitless spectroscopy (SOSS) enablingsimultaneous wavelength coverage between 0.6 and 2.8 \mum at R~700, amode optimized for exoplanet spectroscopy of relatively bright (J<6.3) starsand 4) aperture masking interferometry (AMI) between 2.8 and 4.8 \mumenabling high-contrast (~10^{-3}-10^{-4}) imaging at angular separationsbetween 70 and 400 milliarcsec for relatively bright (M<8) sources. Thispaper presents an overview of the NIRISS instrument, its design, its scientificcapabilities, and a summary of in-flight performance. NIRISS showssignificantly better response shortward of ~2.5\,\mum resulting in 10-40%sensitivity improvement for broadband and low-resolution spectroscopy comparedto pre-flight predictions. Two time-series observations performed duringinstrument commissioning in the SOSS mode yield very stable spectro-photometryperformance within ~10% of the expected noise. The first space-basedcompanion detection of the tight binary star AB Dor AC through AMI wasdemonstrated.