Cherenkov Telescope Array sensitivity to the putative millisecond pulsar population responsible for the Galactic Centre excess. Issue 2 (21st May 2021)

• Record Type: Journal Article
• Authors: Macias, Oscar; van Leijen, Harm; Song, Deheng; Ando, Shin'ichiro; Horiuchi, Shunsaku; Crocker, Roland M
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 506:Issue 2(2021)
• Page Start: 1741
• Page End: 1760
• Publication Date: 2021-05-21
• Subjects: pulsars: general -- dark matter -- gamma-rays: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab1450
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The leading explanation of the Fermi Galactic Centre γ-ray excess is the extended emission from an unresolved population of millisecond pulsars (MSPs) in the Galactic bulge. Such a population would, along with the prompt γ-rays, also inject large quantities of electrons/positrons ( e ± ) into the interstellar medium. These e ± could potentially inverse-Compton (IC) scatter ambient photons into γ-rays that fall within the sensitivity range of the upcoming Cherenkov Telescope Array (CTA). In this article, we examine the detection potential of CTA to this signature by making a realistic estimation of the systematic uncertainties on the Galactic diffuse emission model at TeV-scale γ-ray energies. We forecast that, in the event that e ± injection spectra are harder than E −2, CTA has the potential to robustly discover the IC signature of a putative Galactic bulge MSP population sufficient to explain the Galactic Centre excess for e ± injection efficiencies in the range of ≈2.9–74.1 per cent, or higher, depending on the level of mismodelling of the Galactic diffuse emission components. On the other hand, for spectra softer than E −2.5, a reliable CTA detection would require an unphysically large e ± injection efficiency of ${\gtrsim} 158{{\ \rm per\ cent}}$ . However, even this pessimistic conclusion may be avoided in the plausible event that MSP observational and/or modelling uncertainties can be reduced. We further find that, in the event that an IC signal were detected, CTA can successfully discriminate between an MSP and a dark matter origin for the radiating e ± .