The James Webb Space Telescope Absolute Flux Calibration. V. Near-Infrared Camera Wide Field Slitless Spectroscopy

Abstract

We present the absolute flux and wavelength calibration of the James Webb Space Telescope (JWST) Near-Infrared Camera (NIRCam) Wide Field Slitless Spectroscopy (WFSS) mode. Each of NIRCam's two modules (A and B) provides independent long wavelength (LW) grism spectroscopy over the 2.4-5.0 micron range, with orthogonally oriented R and C grisms. Using commissioning and calibration data from programs 01076, 01536, 01537, 01538, 01479, 01480, 04449, 04498, 06606, and 06628, we have measured the field-dependent geometry and wavelength dispersion of both first and second order spectra across the full detector area. The trace geometry was modeled using two-dimensional third-order polynomials that reproduce the observed spectral positions with an RMS accuracy better than 0.1 pixel. Wavelength calibration, derived from observations of the planetary nebula SMP LMC 58, achieves a precision of 0.65-0.91A for the +1 orders and 0.5A for the +2 orders. Absolute flux calibration, established from observations of the G-type star standard P330E, provides a consistent sensitivity function across all grisms and modules with an absolute flux accuracy of 3\%. The resulting calibration framework defines the geometric, wavelength, and photometric reference for all NIRCam WFSS observations and ensures cross-consistency between modules and grism orientations. These calibrations form the basis for accurate slitless spectroscopy with NIRCam and will support ongoing improvements to the JWST calibration pipeline and data products.