Non-thermal emission in jets and winds: Expected emission and spectral index distributions
8 affiliations
- 1Leibniz Institute for Astrophysics , An der Sternwarte 16, D-14482 Potsdam ,
- 2IUCAA , Post Bag 4 Ganeshkhind, Savitribai Phule Pune University Campus Pune 411007 ,
- 3INAF, Osservatorio Astrofisico di Torino , Strada Osservatorio 20, I-10025 Pino Torinese ,
- 4School of Mathematics, Statistics and Physics , Newcastle University, Newcastle upon Tyne NE1 7RU ,
- 5Durham University Centre for Extragalactic Astronomy, Department of Physics, , Durham DH1 3LE ,
- 6Durham University Institute for Computational Cosmology, Department of Physics, , Durham DH1 3LE ,
- 7National Centre for Radio Astrophysics (NCRA) - Tata Institute of Fundamental Research (TIFR), S. P. Pune University Campus , Pune 411007 ,
- 8Universidad de Concepción Departamento de Astronomía, , Casilla 160-C, Concepción ,
Abstract
The origin of synchrotron emission in compact radio sources associated with active galactic nuclei (AGN) remains poorly understood. In a series of papers, we have examined diagnostic tools to disentangle the dominant underlying processes. In this study, we investigate the in situ evolution of cosmic-ray electrons (CREs) in compact AGN jets and winds, and examine how their evolution shapes the resulting observable radio properties. In jets, CREs experience multiple shock interactions as they propagate along the spine toward the hotspot and flow into the cocoon via backflows. In winds, CREs are predominantly accelerated at the Mach disc, with occasional re-acceleration within turbulent cocoon backflows. The continuous mixing of different CRE populations within the cocoon produces observational signatures that cannot be inferred from instantaneous conditions alone. In all jet simulations, spectral indices are flattest near the hotspot and steepen progressively away from the hotspots. In winds, spectra steepen with increasing distance from the Mach disc, with this trend becoming more pronounced at high radio frequencies due to radiative losses. We find the Mach disc to be a significantly more efficient CRE acceleration site than the forward shock in winds, which weakens as the wind expands to large scales. Since morphology, especially at low resolution, can be ambiguous for compact sources, spatially resolved spectral indices, particularly when combined with emission and polarization signatures, can provide a powerful diagnostic.
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BibTeX
@article{meenakshi2026nonthermal,
title = {{Non-thermal emission in jets and winds: Expected emission and spectral index distributions}},
author = {M Meenakshi and D Mukherjee and G Bodo and P Rossi and C M Harrison and L K Morabito and P Kharb and S Silpa},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag2045},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2045/9003264},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Non-thermal emission in jets and winds: Expected emission and spectral index distributions
AU - M Meenakshi
AU - D Mukherjee
AU - G Bodo
AU - P Rossi
AU - C M Harrison
AU - L K Morabito
AU - P Kharb
AU - S Silpa
PY - 2026
DA - 2026/10/27
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag2045
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2045/9003264
AB - The origin of synchrotron emission in compact radio sources associated with active galactic nuclei (AGN) remains poorly understood. In a series of papers, we have examined diagnostic tools to disentangle the dominant underlying processes. In this study, we investigate the in situ evolution of cosmic-ray electrons (CREs) in compact AGN jets and winds, and examine how their evolution shapes the resulting observable radio properties. In jets, CREs experience multiple shock interactions as they propagate along the spine toward the hotspot and flow into the cocoon via backflows. In winds, CREs are predominantly accelerated at the Mach disc, with occasional re-acceleration within turbulent cocoon backflows. The continuous mixing of different CRE populations within the cocoon produces observational signatures that cannot be inferred from instantaneous conditions alone. In all jet simulations, spectral indices are flattest near the hotspot and steepen progressively away from the hotspots. In winds, spectra steepen with increasing distance from the Mach disc, with this trend becoming more pronounced at high radio frequencies due to radiative losses. We find the Mach disc to be a significantly more efficient CRE acceleration site than the forward shock in winds, which weakens as the wind expands to large scales. Since morphology, especially at low resolution, can be ambiguous for compact sources, spatially resolved spectral indices, particularly when combined with emission and polarization signatures, can provide a powerful diagnostic.
SN - 0035-8711
SN - 1365-2966
ER -