With the development of X-ray astronomy, the understanding of the nature
of the cosmic X-ray background, i.e., the isotropic X-ray radiation
discovered in the early 1960s, has become firmly established. As it
turned out, this background consists of the radiation of many millions
of individual objects: supermassive black holes, absorbing the
surrounding matter in the nuclei of distant galaxies. Despite the
relatively long history of X-ray astronomy, accurate measurements of the
cosmic X-ray background are difficult to realize, mainly due to the need
to separate cosmic radiation from instrumental background arising in
X-ray detectors.
Using a unique technique of spatial modulation of the X-ray background
on the detectors (i.e., two Focal Plane Modules, FPMA and FPMB) of
NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) orbiting
telescope, it was possible to achieve an accuracy of less than one
percent in measuring the cosmic X-ray background. The new method is
sensitive to different background intensities in different sky fields,
which is mainly explained by cosmic variance. The image demonstrates the
new measurement of the cosmic X-ray background intensity (expressed in
units of 10−11 erg s−1 cm−2
deg−2) with NuSTAR. It is compared with the canonical HEAO-1
result, as well as with the more recent INTEGRAL measurements which were
made via Earth occultation manoeuvre (see INTEGRAL POM
March 2006 and
November 2013).
The new cosmic X-ray background measurement (combined
over the fields) with NuSTAR is consistent with the INTEGRAL result, but
about 8% higher than that measured with HEAO-1.
Credits:
"NuSTAR measurement of the cosmic X-ray background in the 3–20 keV energy band"
Roman Krivonos, Daniel Wik, Brian Grefenstette, Kristin Madsen, Kerstin Perez,
Steven Rossland, Sergey Sazonov, Andreas Zoglauer,
2021, Monthly Notices of the Royal Astronomical Society, in press https://doi.org/10.1093/mnras/stab209
