Abstract
The origin of sub-TeV gamma rays detected by the Fermi-Large Area Telescope (LAT) from the Fermi bubbles (FBs) at the Galactic center is still uncertain. In a hadronic model, acceleration of protons and/or nuclei and their subsequent interactions with gas in the bubble volume can produce the observed gamma rays. Recently the High Altitude Water Cherenkov (HAWC) observatory reported an absence of gamma-ray excess from the Northern FB at Galactic latitude, which resulted in flux upper limits in the energy range of 1.2–126 TeV. These upper limits are consistent with the gamma-ray spectrum measured by Fermi-LAT at , where an exponential cutoff at energies is evident. However, the FB gamma-ray spectrum at , without showing any sign of cutoff up to around 1 TeV in the latest results, remains unconstrained. The upcoming Cherenkov Telescope Array (CTA) will perform a Galactic center survey with unprecedented sensitivity in the energy between 20 GeV and 300 TeV. In this work, we perform both morphological and classic on/off analyses with planned CTA deep central and extended survey and estimate the sensitivity of CTA to the FB hadronic gamma-ray flux models that best fit the spectrum at and whose counterpart neutrino flux model best fits the optimistic neutrino spectrum from IceCube Neutrino Observatory. We also perform sensitivity analysis with a future ground-based Cherenkov detector the Large High Altitude Air Shower Observatory (LHAASO). We find that CTA will be able to discover or constrain the FB gamma-ray flux at in the range with planned observation strategy, while LHAASO may constrain emission in the range if systematic uncertainties can be achieved.
- Received 29 November 2018
DOI:https://doi.org/10.1103/PhysRevD.99.083007
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