Noise performance of the JWST/NIRSpec detector system

Stephan M. Birkmann; Marco Sirianni; Pierre Ferruit; Chris J. Willott; Roberto Maiolino; Bernard Rauscher; Catarina Alves de Oliveira; Torsten Böker; Giovanna Giardino; Nora Lützgendorf; Anthony Marston; Elena Puga; Tim Rawle; Maurice te Plate; Peter Jensen; Peter Rumler

doi:10.1117/12.2313524

6 July 2018 Noise performance of the JWST/NIRSpec detector system

Stephan M. Birkmann, Marco Sirianni, Pierre Ferruit, Chris J. Willott, Roberto Maiolino, Bernard Rauscher, Catarina Alves de Oliveira, Torsten Böker, Giovanna Giardino, Nora Lützgendorf, Anthony Marston, Elena Puga, Tim Rawle, Maurice te Plate, Peter Jensen, Peter Rumler

Author Affiliations +

Proceedings Volume 10709, High Energy, Optical, and Infrared Detectors for Astronomy VIII; 1070930 (2018) https://doi.org/10.1117/12.2313524
Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

Abstract

The Near-Infrared Spectrograph (NIRSpec) is one of the four science instruments onboard the James Webb Space Telescope (JWST). The instrument features a focal plane array (FPA) consisting of two 2048 × 2048 HAWAII-2RG sensor chip assemblies (SCAs) with a cutoff wavelength of approximately 5.3 μm. The detectors are read out via a pair of SIDECAR ASICs. To ensure a stable operating environment and best performance, the FPA is temperature controlled via a dedicated control loop by the NIRSpec focal plane electronics. The targeted in-orbit operating temperature of the NIRSpec FPA is close to 42.8 K. Due to the low background levels that the JWST will provide, most NIRSpec observations of very faint targets will be detector noise limited. Therefore, stringent noise requirements on the detector system were put in place. In order to meet these requirements, NIRSpec offers a dedicated readout mode for its detectors that is called improved reference sampling and subtraction (IRS²). In this paper we present the noise performance of the NIRSpec detectors as a function of readout mode and exposure parameters. We find that the NIRSpec detector system meets its stringent noise requirement of 6 electrons total noise in a ∼ 1000 second exposure. We also highlight the types and effects of different kinds of bad pixels that are present in the detectors in small numbers.

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Stephan M. Birkmann, Marco Sirianni, Pierre Ferruit, Chris J. Willott, Roberto Maiolino, Bernard Rauscher, Catarina Alves de Oliveira, Torsten Böker, Giovanna Giardino, Nora Lützgendorf, Anthony Marston, Elena Puga, Tim Rawle, Maurice te Plate, Peter Jensen, and Peter Rumler "Noise performance of the JWST/NIRSpec detector system", Proc. SPIE 10709, High Energy, Optical, and Infrared Detectors for Astronomy VIII, 1070930 (6 July 2018); https://doi.org/10.1117/12.2313524

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