Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport
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 (∼ 13--30,σ) from either site. Under optimistic background assumptions, CTAO can distinguish changes of Δγ1 ≃ 0.2 in the high-energy injection index and ΔB ≃ 2,μG in magnetic-field strength. For Monogem, compact bubbles with RSDZ≈30,pc can be distinguished from extended (≳50,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 ≲10%, indicating robustness against plausible diffuse-background mismodelling.
Related
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BibTeX
@misc{li2026geminga,
title = {{Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport}},
author = {Youyou Li and Oscar Macias and Manuela Vecchi and Shinichiro Ando},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.05245},
eprint = {2607.05245},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.05245},
}
RIS
TY - UNPB
TI - Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport
AU - Youyou Li
AU - Oscar Macias
AU - Manuela Vecchi
AU - Shinichiro Ando
PY - 2026
DA - 2026/09/02
PB - arXiv
DO - 10.48550/arxiv.2607.05245
UR - https://arxiv.org/abs/2607.05245
AB - 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 (∼ 13--30,σ) from either site. Under optimistic background assumptions, CTAO can distinguish changes of Δγ_1 ≃ 0.2 in the high-energy injection index and ΔB ≃ 2,μG in magnetic-field strength. For Monogem, compact bubbles with R_SDZ≈30,pc can be distinguished from extended (≳50,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 ≲10%, indicating robustness against plausible diffuse-background mismodelling.
ER -