Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments
The unstable isotope ^60 Fe, with a half-life of 2.6 million years, is produced primarily in supernova explosions. The observed presence of ^60 Fe in cosmic rays and its detection in deep-sea crusts and sediments suggest two possible scenarios: either the direct acceleration of ^60 Fe from supernova...
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2025-01-01
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| author | Xin-Yue Shi Martin Pohl Michael M. Schulreich |
| author_facet | Xin-Yue Shi Martin Pohl Michael M. Schulreich |
| author_sort | Xin-Yue Shi |
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| description | The unstable isotope ^60 Fe, with a half-life of 2.6 million years, is produced primarily in supernova explosions. The observed presence of ^60 Fe in cosmic rays and its detection in deep-sea crusts and sediments suggest two possible scenarios: either the direct acceleration of ^60 Fe from supernova ejecta or its enrichment in the circumstellar material surrounding supernova progenitors, which indicates cosmic ray production in clusters of supernovae. Focusing on the latter scenario, we consider an environment shaped by successive supernova explosions, reminiscent of the Local Bubble around the time of the most recent supernova explosion. We independently tracked the evolution of the ^60 Fe mass ratio within the Local Bubble using passive scalars. To investigate the spectra of protons and ^60 Fe, we explicitly modeled cosmic-ray acceleration and transport at the remnant of the last supernova by simultaneously solving the hydrodynamical equations for the supernova outflow and the transport equations for cosmic rays, scattering turbulence, and large-scale magnetic field, using the time-dependent acceleration code Radiation Acceleration Transport Parallel Code. The main uncertainty in our prediction of the local ^60 Fe flux at about pc = 1 GeV nuc ^−1 is the magnetic-field structure in the Local Bubble and the cosmic-ray diffusion beyond the approximately 100 kyr of evolution covered by our study. We found that if the standard galactic propagation applies, the local ^60 Fe flux would be around 3% of that measured. If there is a sustained reduction in the diffusion coefficient at and near the Local Bubble, then the expected ^60 Fe flux could be up to 30% of that measured. |
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| spelling | doaj-art-ab16cefb9b774ca78591abf5cfa758b32025-08-20T03:58:45ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01988225510.3847/1538-4357/adea4cAcceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched EnvironmentsXin-Yue Shi0https://orcid.org/0000-0003-1244-172XMartin Pohl1https://orcid.org/0000-0001-7861-1707Michael M. Schulreich2https://orcid.org/0000-0001-7761-9766Department of Astronomy, Nanjing University , 163 Xianlin Avenue, Nanjing 210023, People’s Republic of China; Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University , Ministry of Education, Nanjing, People’s Republic of China; Deutsches Elektronen-Synchrotron DESY , Platanenallee 6, 15738 Zeuthen, GermanyDeutsches Elektronen-Synchrotron DESY , Platanenallee 6, 15738 Zeuthen, Germany; Institute of Physics and Astronomy, University of Potsdam , 14476 Potsdam, GermanyZentrum für Astronomie und Astrophysik, Technische Universität Berlin , Hardenbergstraße 36, 10623 Berlin, GermanyThe unstable isotope ^60 Fe, with a half-life of 2.6 million years, is produced primarily in supernova explosions. The observed presence of ^60 Fe in cosmic rays and its detection in deep-sea crusts and sediments suggest two possible scenarios: either the direct acceleration of ^60 Fe from supernova ejecta or its enrichment in the circumstellar material surrounding supernova progenitors, which indicates cosmic ray production in clusters of supernovae. Focusing on the latter scenario, we consider an environment shaped by successive supernova explosions, reminiscent of the Local Bubble around the time of the most recent supernova explosion. We independently tracked the evolution of the ^60 Fe mass ratio within the Local Bubble using passive scalars. To investigate the spectra of protons and ^60 Fe, we explicitly modeled cosmic-ray acceleration and transport at the remnant of the last supernova by simultaneously solving the hydrodynamical equations for the supernova outflow and the transport equations for cosmic rays, scattering turbulence, and large-scale magnetic field, using the time-dependent acceleration code Radiation Acceleration Transport Parallel Code. The main uncertainty in our prediction of the local ^60 Fe flux at about pc = 1 GeV nuc ^−1 is the magnetic-field structure in the Local Bubble and the cosmic-ray diffusion beyond the approximately 100 kyr of evolution covered by our study. We found that if the standard galactic propagation applies, the local ^60 Fe flux would be around 3% of that measured. If there is a sustained reduction in the diffusion coefficient at and near the Local Bubble, then the expected ^60 Fe flux could be up to 30% of that measured.https://doi.org/10.3847/1538-4357/adea4cCosmic raysSupernova remnantsSuperbubbles |
| spellingShingle | Xin-Yue Shi Martin Pohl Michael M. Schulreich Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments The Astrophysical Journal Cosmic rays Supernova remnants Superbubbles |
| title | Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments |
| title_full | Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments |
| title_fullStr | Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments |
| title_full_unstemmed | Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments |
| title_short | Acceleration and Transport of the Unstable Cosmic-Ray Isotope 60Fe in Supernova-enriched Environments |
| title_sort | acceleration and transport of the unstable cosmic ray isotope 60fe in supernova enriched environments |
| topic | Cosmic rays Supernova remnants Superbubbles |
| url | https://doi.org/10.3847/1538-4357/adea4c |
| work_keys_str_mv | AT xinyueshi accelerationandtransportoftheunstablecosmicrayisotope60feinsupernovaenrichedenvironments AT martinpohl accelerationandtransportoftheunstablecosmicrayisotope60feinsupernovaenrichedenvironments AT michaelmschulreich accelerationandtransportoftheunstablecosmicrayisotope60feinsupernovaenrichedenvironments |