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This study examines TeV halos around two middle-aged pulsars, Geminga and Monogem, which show regions of unusually slow cosmic ray diffusion. Researchers used GALPROP simulations to model how electrons and positrons propagate from these pulsars and assessed whether the upcoming Cherenkov Telescope Array Observatory (CTAO) can measure key properties like magnetic field strength and the size of slow-diffusion zones. Their models predict CTAO will detect both halos with high statistical significance and distinguish between different physical parameters that affect cosmic ray transport.
Why it matters
Understanding how cosmic rays diffuse around pulsars helps explain the local positron excess observed in space and improves models of particle transport through the galaxy. The findings demonstrate that next-generation gamma-ray observatories will provide critical data to test theories of cosmic ray propagation.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
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.
Source: Geminga and Monogem in the CTAO Era: Probing TeV Halos and Cosmic-Ray Transport