Preprint Models Predict Microquasar Remnants Reach 10^35-10^36 erg/s Only in Super-Eddington Cases
Time-dependent modeling of particle transport in extinct microquasar cocoons shows that only super-Eddington remnants reach detectable broadband luminosities, controlled primarily by surface brightness rather than total flux. The work identifies a hidden population of extended non-thermal Galactic sources whose radio and X-ray signatures should be targeted by next-generation interferometers. Direct detection remains challenging and will require both high surface-brightness sensitivity and multi-wavelength cross-correlation.
The authors solve the transport equation for relativistic electrons and protons inside the cocoon, incorporating second-order Fermi acceleration from internal turbulence and adiabatic losses at the expanding shell. They track synchrotron, inverse-Compton, and pion-decay emission from radio through TeV gamma rays plus thermal X-rays from the shocked shell, running separate grids for sub-Eddington and super-Eddington jet power histories. Surface brightness at 1.3 GHz falls below 10^-19 W m^-2 Hz^-1 sr^-1 within 10^4 years, rendering most remnants undetectable as discrete sources even when integrated flux would be measurable.
These results refine the hidden PeVatron hypothesis by showing that only the rare super-Eddington remnants can sustain the required particle energy density long after the central engine shuts off. The modeling connects directly to the observed population of unidentified extended Galactic gamma-ray sources and to the missing cosmic-ray budget above the knee, suggesting MQRs could supply a non-negligible fraction of Galactic PeV particles if their occurrence rate matches the known microquasar birth rate.
Future wide-field surveys with SKA and CTA will test the prediction that powerful remnants appear first as low-surface-brightness radio cocoons paired with soft X-ray shells. Sub-Eddington systems will likely remain invisible unless viewed against bright background emission or through secondary hadronic signatures in nearby molecular clouds.
Abaroa: SKA1-MID early science will report at least one extended 1.3 GHz cocoon matching the modeled 10^-19 W m^-2 Hz^-1 sr^-1 surface brightness within three years of full operations.
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2608.17000)
- [2]Supporting Source(https://arxiv.org/abs/2301.04237)
- [3]Supporting Source(https://doi.org/10.1038/s41550-022-01642-4)