Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport

Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport
Youyou Li, Oscar Macias, Manuela Vecchi, Shinichiro Ando
arXiv:2607.05245v2 Announce Type: replace
Abstract: TeV halos around Geminga and Monogem (B0656+14) reveal regions of strongly suppressed diffusion near middle-aged pulsars. Determining the sizes and magnetic-field strengths of these slow-diffusion zones is important for modelling lepton transport and assessing their contribution to the local positron excess. The Cherenkov Telescope Array Observatory (CTAO) will provide arcminute-scale imaging of extended gamma-ray emission. We construct two-zone diffusion models for Geminga and Monogem with GALPROP v57, injecting electrons and positrons according to the pulsar spin-down history and following their propagation through an evolving slow-diffusion bubble and the ambient interstellar medium. Calibrating to HAWC and Fermi-LAT measurements, we forward-fold the models through official CTAO instrument response functions, including realistic diffuse and instrumental backgrounds. For 50 h observations, both halos are detected with high significance ($sim 13$–$30,sigma$) from either site. Under optimistic background assumptions, CTAO can distinguish changes of $Deltagamma_1 simeq 0.2$ in the high-energy injection index and $Delta B simeq 2,mu{rm G}$ in magnetic-field strength. For Monogem, compact bubbles with $R_{rm SDZ}approx30,{rm pc}$ can be distinguished from extended ($gtrsim50,{rm pc}$) cases, although very large bubbles remain degenerate because of the finite field of view. Using an alternative Galactic diffuse template in the fit changes detection significances and parameter sensitivities by $lesssim10%$, indicating robustness against plausible diffuse-background mismodelling.arXiv:2607.05245v2 Announce Type: replace
Abstract: TeV halos around Geminga and Monogem (B0656+14) reveal regions of strongly suppressed diffusion near middle-aged pulsars. Determining the sizes and magnetic-field strengths of these slow-diffusion zones is important for modelling lepton transport and assessing their contribution to the local positron excess. The Cherenkov Telescope Array Observatory (CTAO) will provide arcminute-scale imaging of extended gamma-ray emission. We construct two-zone diffusion models for Geminga and Monogem with GALPROP v57, injecting electrons and positrons according to the pulsar spin-down history and following their propagation through an evolving slow-diffusion bubble and the ambient interstellar medium. Calibrating to HAWC and Fermi-LAT measurements, we forward-fold the models through official CTAO instrument response functions, including realistic diffuse and instrumental backgrounds. For 50 h observations, both halos are detected with high significance ($sim 13$–$30,sigma$) from either site. Under optimistic background assumptions, CTAO can distinguish changes of $Deltagamma_1 simeq 0.2$ in the high-energy injection index and $Delta B simeq 2,mu{rm G}$ in magnetic-field strength. For Monogem, compact bubbles with $R_{rm SDZ}approx30,{rm pc}$ can be distinguished from extended ($gtrsim50,{rm pc}$) cases, although very large bubbles remain degenerate because of the finite field of view. Using an alternative Galactic diffuse template in the fit changes detection significances and parameter sensitivities by $lesssim10%$, indicating robustness against plausible diffuse-background mismodelling.