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Published April 2021 | Published + Accepted Version
Journal Article Open

NuSTAR measurement of the cosmic X-ray background in the 3–20 keV energy band

Abstract

We present measurements of the intensity of the cosmic X-ray background (CXB) with the Nuclear Spectroscopic Telescope Array (NuSTAR) telescope in the 3–20 keV energy range. Our method uses spatial modulation of the CXB signal on the NuSTAR detectors through the telescope's side aperture. Based on the NuSTAR observations of selected extragalactic fields with a total exposure of 7 Ms, we have estimated the CXB 3–20 keV flux to be 2.8 × 10⁻¹¹ erg s⁻¹ cm⁻² deg⁻², which is ∼8 per cent higher than that measured with HEAO-1 and consistent with the INTEGRAL measurement. The inferred CXB spectral shape in the 3–20 keV energy band is consistent with the canonical model of Gruber et al. We demonstrate that the spatially modulated CXB signal measured by NuSTAR is not contaminated by systematic noise and is limited by photon statistics. The measured relative scatter of the CXB intensity between different sky directions is compatible with cosmic variance, which opens new possibilities for studying CXB anisotropy over the whole sky with NuSTAR.

Additional Information

© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2021 January 21. Received 2021 January 11; in original form 2020 November 21. Published: 04 February 2021. This work has made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has made use of the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC. RK and SS acknowledge support for this research from the Russian Science Foundation (grant 19-12-00396). DW and SR acknowledge support for this work from the NASA Astrophysics Data Analysis Program 80NSSC18K0686. Data Availability: This work is based on the NuSTAR data publicly available through the HEASARC Archive (https://heasarc.gsfc.nasa.gov).

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Accepted Version - 2011.11469.pdf

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Additional details

Created:
August 20, 2023
Modified:
October 23, 2023