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

Krivonos, Roman and Wik, Daniel and Grefenstette, Brian and Madsen, Kristin and Perez, Kerstin and Rossland, Steven and Sazonov, Sergey and Zoglauer, Andreas (2021) NuSTAR measurement of the cosmic X-ray background in the 3–20 keV energy band. Monthly Notices of the Royal Astronomical Society, 502 (3). pp. 3966-3975. ISSN 0035-8711. doi:10.1093/mnras/stab209.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
https://heasarc.gsfc.nasa.govRelated ItemNASA HEASARC Archive
Krivonos, Roman0000-0003-2737-5673
Wik, Daniel0000-0001-9110-2245
Grefenstette, Brian0000-0002-1984-2932
Madsen, Kristin0000-0003-1252-4891
Perez, Kerstin0000-0002-6404-4737
Zoglauer, Andreas0000-0001-9067-3150
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 ( 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 (
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Russian Science Foundation19-12-00396
Subject Keywords:instrumentation: detectors – methods: data analysis – galaxies: active – cosmic background radiation – X-rays: general
Issue or Number:3
Record Number:CaltechAUTHORS:20210601-100040210
Persistent URL:
Official Citation:Roman Krivonos, Daniel Wik, Brian Grefenstette, Kristin Madsen, Kerstin Perez, Steven Rossland, Sergey Sazonov, Andreas Zoglauer, NuSTAR measurement of the cosmic X-ray background in the 3–20 keV energy band, Monthly Notices of the Royal Astronomical Society, Volume 502, Issue 3, April 2021, Pages 3966–3975,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109320
Deposited By: Tony Diaz
Deposited On:01 Jun 2021 18:11
Last Modified:01 Jun 2021 18:11

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