Kavli Affiliate: Shunsaku Horiuchi
| First 5 Authors: Oscar Macias, Harm van Leijen, Deheng Song, Shin’ichiro Ando, Shunsaku Horiuchi
| Summary:
The leading explanation of the $textit{Fermi}$ Galactic center $gamma$-ray
excess is the extended emission from a unresolved population of millisecond
pulsars (MSPs) in the Galactic bulge. Such a population would, along with the
prompt $gamma$ rays, also inject large quantities of electrons/positrons
($e^pm$) into the interstellar medium. These $e^pm$ could potentially
inverse-Compton (IC) scatter ambient photons into $gamma$ 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 $gamma$-ray energies. We forecast that, in
the event that $e^pm$ 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 GCE for $e^pm$ injection efficiencies
in the range $approx 2.9-74.1%$, or higher, depending on the level of
mismodeling 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 $e^pm$ injection efficiency of $gtrsim 158%$. However,
even this pessimistic conclusion may be avoided in the plausible event that MSP
observational and/or modeling 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 $e^pm$.
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