2022 Fiscal Year Research-status Report
Combined Spectrum and Anisotropy Study of Cosmic Rays from the Vela SNR with CALET
| Project/Area Number |
21K03604
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| Research Institution | Waseda University |
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Principal Investigator |
Motz Holger 早稲田大学, 理工学術院, 准教授(任期付) (30647904)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Keywords | High Energy Cosmic Rays / Vela Supernova Remnant / Cosmic Ray Anisotropy / Cosmic Ray Propagation |
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| Outline of Annual Research Achievements |
Since the spectral and anisotropy electron cosmic-ray signatures of the Vela SNR depend strongly on the cosmic-ray propagation conditions, strong effort was put into improving the underlying propagation model. The propagation parameters are determined in a random walk optimization by comparing measured nuclei cosmic spectra with the output of the numerical propagation code DRAGON. The developed model explains the differences in the measured nuclei spectra by propagation effects only, without the need for species-specific acceleration mechanisms, and matches well the measured nuclei spectra as well as primary-secondary ratios.
Furthermore, an interpretation model for the all-electron spectrum by CALET and positron-only spectrum by AMS-02 based on randomly sampled individual point sources (SNR, pulsars) throughout the galaxy was developed, replacing the phenomenological power-law parameterization for the contribution from distant astrophysical sources. This provides the source spectrum power-law index and cutoff energy ranges allowed by the need to explain the lower energy parts of the spectra by the distant sources, which then can be applied to constrain the range of possible source-spectrum parameters for the Vela SNR.
The propagation model and astrophysical source interpretation have been (or will soon be) presented on their own or in the context of indirect dark matter search with CALET. Work on the planned combination of the un-binned likelihood analysis method with the event-by-event anisotropy analysis presented in the research plan is ongoing.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Compared to the schedule in the research plan, more focus was put on refining the cosmic-ray propagation model and on developing a model to fit the whole energy range of the electron and positron spectra with the individually calculated overlapping spectra of randomly sampled point sources (SNRs, pulsars). These efforts became necessary as more nuclei spectra data became available, constraining the propagation parameters, and various all-individual source interpretations of the electron and positron spectra were published.
While these studies further delayed the initially planned systematic study of various propagation and source spectra scenarios for the Vela SNR, they promise to greatly constrain the parameter space of conditions that need to be considered. As a positive or negative result on a Vela signature becomes more meaningful with better constrained propagation and source parameters, and also the time and effort needed for evaluating the data is reduced, the project could be still considered to progress towards the goal in a rather smooth manner.
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| Strategy for Future Research Activity |
The un-binned likelihood analysis method for anisotropy explained in the research plan is being merged with a recently developed un-binned likelihood method for the spectrum, and will be tested on calculations of reference models with and without significant spectral contribution from the Vela SNR.
By processing many samples of randomly generated SNR and pulsar populations throughout the galaxy in the framework of the above mentioned individual source interpretation model, favored ranges and constraints on the key parameters for SNR cosmic-ray sources (injection spectrum power index, spectrum cut-off energy, total emitted energy) are going to be derived. This information will be used to choose suitable parameters for the Vela reference models which will be compared to CALET TeV-range electron event data.
Before application of the Vela specific fixed-direction anisotropy analysis, a general direction anisotropy analysis with the latest CALET electron event data will be performed and limits on the cosmic-ray dipole anisotropy published.
As part of the fitting of results from calculation with DRAGON to the measured nuclei spectra for determining the propagation parameters, the possibility that the contribution of Vela to the nuclei spectra is the cause of the spectral hardening found around 1 TV rigidity (as opposed to a break in the rigidity dependence of the diffusion coefficient) will be investigated, to present a comprehensive picture of the influence of the nearby SNR sources on the cosmic-ray spectra.
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