Prospects on detection of the Fermi Bubbles with CTAO

Abstract

In 2010, the Fermi Gamma-ray Space Telescope observed two gamma-ray emitting structures, the Fermi Bubbles (FBs), that extend up to 55° above and below the Galactic plane and that seem to emanate from the Galactic center region. Although the spectrum at latitudes |b| > 10° has a softening or a cutoff around 100 GeV, the one at the base of the FBs, |b| <10°, extends up to about 1 TeV without a significant cutoff in the Fermi LAT data. The mechanism behind the FBs production is currently under debate. More observations of the FBs at different energies are required to improve our understanding of their origin. Recently, H.E.S.S. and HAWC observatory have set upper limits on the FBs. In this work, we assess the sensitivity of the Cherenkov Telescope Array Observatory (CTAO) using the "alpha configuration" in the South site to detect the FBs and investigate the optimal strategies for their detection at low latitudes. We simulate the observations using the official CTAO science tool gammapy, considering several benchmark models for the FBs and the interstellar emission and test different observational strategies taking advantage of the proposed CTAO consortium surveys. We use these simulations to estimate the CTAO sensitivity to the FBs.

Figures (5)

• Figure 1: Left: Counts map for CR Background including the pointing positions of the GC survey. Center: Counts map for the Interstellar Emission (IE), corresponding to the VariableMin benchmark model. Right: Counts map for the FBs. All of the plots show the sum of counts over the whole considered energy range.
• Figure 2: Models for the different emission components in our RoI. The FBs model is obtained by fitting the low latitude spectrum in Fermi (black stars). We take the Max and Min benchmarks for both the Base and Variable IE models of DeLaTorre (4 models in total).
• Figure 3: Left: Recovery of the injected FBs spectrum for 525 hours in our RoI. Upper limits are shown together with $1\sigma$ uncertainties for each point. Right: Capability of CTAO to recover the energy cutoff for different spectral indices.
• Figure 4: Recovery of the injected FBs spectrum for 50 hours in our RoI. Upper limits are shown together with $1\sigma$ uncertainties for each point.
• Figure 5: Left: Impact of systematic uncertainties on the recovery of the FBs. Right: Impact of systematic uncertainties on the estimation of the energy cutoff.