The In-Flight Noise Performance of the JWST/NIRSpec Detector System

TL;DR

This paper reports on the in-flight noise performance of the JWST/NIRSpec detector system, highlighting its noise reduction techniques, operational conditions, and suitability for high-precision astronomical observations.

Contribution

It provides the first in-flight characterization of NIRSpec's detector noise performance, including the effectiveness of IRS2 readout mode and subarray optimization.

Findings

Reduced 1/f and correlated noise with IRS2 mode

Dark signal levels characterized in-flight

Detectors meet noise requirements for precise spectroscopy

Abstract

The Near-Infrared Spectrograph (NIRSpec) is one the four focal plane instruments on the James Webb Space Telescope (JWST) which was launched on December 25, 2021. We present the in-flight status and performance of NIRSpec's detector system as derived from the instrument commissioning data. The instrument features two 2048 x 2048 HAWAII-2RG sensor chip assemblies (SCAs) that are operated at a temperature of about 42.8 K and are read out via a pair of SIDECAR ASICs. NIRSpec supports "Improved Reference Sampling and Subtraction" (IRS2) readout mode that was designed to meet NIRSpec's stringent noise requirements and to reduce 1/f and correlated noise. In addition, NIRSpec features subarrays optimized for bright object time series observations, e.g. for the observation of exoplanet transit around bright host stars. We focus on the dark signal as well as the read and total noise performance of the detectors.