Kavli Affiliate: Claudio Ricci
| First 5 Authors: Francesca Civano, Xiurui Zhao, Peter Boorman, Stefano Marchesi, Tonima Ananna
| Summary:
Since the discovery of the cosmic X-ray background (CXB), astronomers have
strived to understand the accreting supermassive black holes (SMBHs)
contributing to its peak in the 10-40 keV band. Existing soft X-ray telescopes
could study this population up to only 10 keV, and, while NuSTAR (focusing on
3–24 keV) made great progress, it also left significant uncertainties in
characterizing the hard X-ray population, crucial for calibrating current
population synthesis models. This paper presents an in-depth analysis of
simulations of two extragalactic surveys (deep and wide) with the High-Energy
X-ray Probe (HEX-P), each observed for 2 Ms. Applying established source
detection techniques, we show that HEX-P surveys will reach a flux of
$sim$10$^{-15}$ erg s$^{-1}$ cm$^{-2}$ in the 10-40 keV band, an order of
magnitude fainter than current NuSTAR surveys. With the large sample of new
hard X-ray detected sources ($sim2000$), we showcase HEX-P’s ability to
resolve more than 80% of the CXB up to 40 keV into individual sources. The
expected precision of HEX-P’s resolved background measurement will allow us to
distinguish between population synthesis models of SMBH growth. HEX-P leverages
accurate broadband (0.5-40 keV) spectral analysis and the combination of soft
and hard X-ray colors to provide obscuration constraints even for the fainter
sources, with the overall objective of measuring the Compton-thick fraction.
With unprecedented sensitivity in the 10–40 keV band, HEX-P will explore the
hard X-ray emission from AGN to flux limits never reached before, thus
expanding the parameter space for serendipitous discoveries. Consequently, it
is plausible that new models will be needed to capture the population HEX-P
will unveil.
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