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

TL;DR

This paper details the calibration process for JWST's NIRCam Wide Field Slitless Spectroscopy mode, establishing precise geometric, wavelength, and flux calibration to enable accurate near-infrared slitless spectroscopic observations.

Contribution

It provides the first comprehensive calibration framework for NIRCam WFSS, including geometric, wavelength, and flux calibration with high accuracy, ensuring reliable data for JWST observations.

Findings

Achieved RMS accuracy better than 0.1 pixel in spectral position

Wavelength calibration precision of 0.5-0.91 Å

Flux calibration accuracy of 3% across all modules

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.