Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A
Young supernova remnants (SNRs) are believed to be the origin of energetic cosmic rays (CRs) below the “knee” of their spectrum at ∼3 PeV (10 ^15 eV). Nevertheless, the precise location, duration, and operation of CR acceleration in young SNRs are open questions. Here, we report on multiepoch X-ray...
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2025-01-01
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| author | Jooyun Woo Kaya Mori Charles J. Hailey Elizabeth Spira-Savett Aya Bamba Brian W. Grefenstette Thomas B. Humensky Reshmi Mukherjee Samar Safi-Harb Tea Temim Naomi Tsuji |
| author_facet | Jooyun Woo Kaya Mori Charles J. Hailey Elizabeth Spira-Savett Aya Bamba Brian W. Grefenstette Thomas B. Humensky Reshmi Mukherjee Samar Safi-Harb Tea Temim Naomi Tsuji |
| author_sort | Jooyun Woo |
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| description | Young supernova remnants (SNRs) are believed to be the origin of energetic cosmic rays (CRs) below the “knee” of their spectrum at ∼3 PeV (10 ^15 eV). Nevertheless, the precise location, duration, and operation of CR acceleration in young SNRs are open questions. Here, we report on multiepoch X-ray observations of Cassiopeia A (Cas A), a 350 yr old SNR, in the 15–50 keV band that probes the most energetic CR electrons. The observed X-ray flux decrease (15% ± 1% over 10 yr), contrary to the expected >90% decrease based on previous radio, X-ray, and gamma-ray observations, provides unambiguous evidence for CR electron acceleration operating in Cas A. A temporal model for the radio and X-ray data accounting for electron cooling and continuous injection finds that the freshly injected electron spectrum is significantly harder (exponential cutoff power-law index q = 2.15), and its cutoff energy is much higher ( E _cut = 36 TeV), than the relic electron spectrum ( q = 2.44 ± 0.03, E _cut = 4 ± 1 TeV). Both electron spectra are naturally explained by the recently developed modified nonlinear diffusive shock acceleration (mNLDSA) mechanism. The CR protons producing the observed gamma rays are likely accelerated at the same location by the same mechanism as the injected electrons. The Cas A observations and spectral modeling represent the first time radio, X-ray, gamma-ray, and CR spectra have been self-consistently tied to a specific acceleration mechanism—mNLDSA—in a young SNR. |
| format | Article |
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| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-1d35bbd8dda446fd8d0598eac8a85a742025-01-17T09:43:52ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0197917210.3847/1538-4357/ad98f1Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia AJooyun Woo0https://orcid.org/0009-0001-6471-1405Kaya Mori1https://orcid.org/0000-0002-9709-5389Charles J. Hailey2https://orcid.org/0000-0002-3681-145XElizabeth Spira-Savett3https://orcid.org/0009-0009-6387-7241Aya Bamba4https://orcid.org/0000-0003-0890-4920Brian W. Grefenstette5https://orcid.org/0000-0002-1984-2932Thomas B. Humensky6https://orcid.org/0000-0002-1432-7771Reshmi Mukherjee7https://orcid.org/0000-0002-3223-0754Samar Safi-Harb8https://orcid.org/0000-0001-6189-7665Tea Temim9https://orcid.org/0000-0001-7380-3144Naomi Tsuji10https://orcid.org/0000-0001-7209-9204Columbia Astrophysics Laboratory, Columbia University , 538 West 120th Street, New York, NY 10027, USA ; jw3855@columbia.eduColumbia Astrophysics Laboratory, Columbia University , 538 West 120th Street, New York, NY 10027, USA ; jw3855@columbia.eduColumbia Astrophysics Laboratory, Columbia University , 538 West 120th Street, New York, NY 10027, USA ; jw3855@columbia.eduDepartment of Physics and Astronomy , Barnard College, 3009 Broadway, New York, NY 10027, USADepartment of Physics, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan; Research Center for the Early Universe, School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan; Trans-Scale Quantum Science Institute, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, JapanSpace Radiation Lab, California Institute of Technology , 1200 East California Boulevard, Pasadena, CA 91125, USAGoddard Space Flight Center , NASA, 8800 Greenbelt Road, Greenbelt, MD 20771, USA; Department of Physics, University of Maryland , 4150 Campus Drive, College Park, MD 20742, USADepartment of Physics and Astronomy , Barnard College, 3009 Broadway, New York, NY 10027, USADepartment of Physics and Astronomy, University of Manitoba , 30A Sifton Road, Winnipeg, MB R3T 2N2, CanadaDepartment of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 08544, USAFaculty of Science, Kanagawa University , 3-27-1 Rokukakubashi, Kanagawa-ku, Yokohama-shi, Kanagawa, 221-8686, JapanYoung supernova remnants (SNRs) are believed to be the origin of energetic cosmic rays (CRs) below the “knee” of their spectrum at ∼3 PeV (10 ^15 eV). Nevertheless, the precise location, duration, and operation of CR acceleration in young SNRs are open questions. Here, we report on multiepoch X-ray observations of Cassiopeia A (Cas A), a 350 yr old SNR, in the 15–50 keV band that probes the most energetic CR electrons. The observed X-ray flux decrease (15% ± 1% over 10 yr), contrary to the expected >90% decrease based on previous radio, X-ray, and gamma-ray observations, provides unambiguous evidence for CR electron acceleration operating in Cas A. A temporal model for the radio and X-ray data accounting for electron cooling and continuous injection finds that the freshly injected electron spectrum is significantly harder (exponential cutoff power-law index q = 2.15), and its cutoff energy is much higher ( E _cut = 36 TeV), than the relic electron spectrum ( q = 2.44 ± 0.03, E _cut = 4 ± 1 TeV). Both electron spectra are naturally explained by the recently developed modified nonlinear diffusive shock acceleration (mNLDSA) mechanism. The CR protons producing the observed gamma rays are likely accelerated at the same location by the same mechanism as the injected electrons. The Cas A observations and spectral modeling represent the first time radio, X-ray, gamma-ray, and CR spectra have been self-consistently tied to a specific acceleration mechanism—mNLDSA—in a young SNR.https://doi.org/10.3847/1538-4357/ad98f1Supernova remnantsGalactic cosmic raysX-ray astronomy |
| spellingShingle | Jooyun Woo Kaya Mori Charles J. Hailey Elizabeth Spira-Savett Aya Bamba Brian W. Grefenstette Thomas B. Humensky Reshmi Mukherjee Samar Safi-Harb Tea Temim Naomi Tsuji Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A The Astrophysical Journal Supernova remnants Galactic cosmic rays X-ray astronomy |
| title | Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A |
| title_full | Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A |
| title_fullStr | Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A |
| title_full_unstemmed | Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A |
| title_short | Spectrum and Location of Ongoing Extreme Particle Acceleration in Cassiopeia A |
| title_sort | spectrum and location of ongoing extreme particle acceleration in cassiopeia a |
| topic | Supernova remnants Galactic cosmic rays X-ray astronomy |
| url | https://doi.org/10.3847/1538-4357/ad98f1 |
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