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Post Info TOPIC: Two million year old supernova
Blobrana


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Local supernova
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Title: A supernova at 50 pc: Effects on the Earth's atmosphere and biota
Author: A.L Melott (Kansas), B.C. Thomas, M. Kachelriess, D.V. Semikoz, A. C. Overholt

Recent 60Fe results have suggested that the estimated distances of supernovae in the last few million years should be reduced from 100 pc to 50 pc. Two events or series of events are suggested, one about 2.7 million years to 1.7 million years ago, and another may at 6.5 to 8.7 million years ago. We ask what effects such supernovae are expected to have on the terrestrial atmosphere and biota. Assuming that the Local Bubble was formed before the event being considered, and that the supernova and the Earth were both inside a weak, disordered magnetic field at that time, TeV-PeV cosmic rays at Earth will increase by a factor of a few hundred. Tropospheric ionization will increase proportionately, and the overall muon radiation load on terrestrial organisms will increase by a factor of 150. All return to pre-burst levels within 10kyr. In the case of an ordered magnetic field, effects depend strongly on the field orientation. The upper bound in this case is with a largely coherent field aligned along the line of sight to the supernova, in which case TeV-PeV cosmic ray flux increases are 10^4; in the case of a transverse field they are below current levels. We suggest a substantial increase in the extended effects of supernovae on Earth and in the lethal distance estimate; more work is needed.This paper is an explicit followup to Thomas et al. (2016). We also here provide more detail on the computational procedures used in both works.

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Blobrana


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RE: Two million year old supernova
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Local supernova 2 million years ago solves cosmic ray puzzle

All signs point to a supernova. A stellar explosion 2 million years ago that flooded our neighbourhood with charged particles could be the answer to several cosmic puzzles. For years, astrophysicists have struggled to explain why there are so many high-energy cosmic rays - speeding charged particles that hit Earth from all directions. We'd expect most to have fled the galaxy long before reaching us, yet we see a lot of protons, as well as the antiprotons and positrons they produce in collisions.
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Blobrana


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Title: Signatures of a two million year old supernova in the spectra of cosmic ray protons, antiprotons and positrons
Author: M. Kachelriess, A. Neronov, D.V. Semikoz

The locally observed cosmic ray spectrum has several puzzling features, such as the excess of positrons and antiprotons above ~20 GeV and the discrepancy in the slopes of the spectra of cosmic ray protons and heavier nuclei in the TeV-PeV energy range. We show that these features are consistently explained by a nearby source which was active ~2 Myr ago and has injected (1-2) x 10^50 erg in cosmic rays. The transient nature of the source and its overall energy budget point to the supernova origin of this local cosmic ray source. The age of the supernova suggests that the local cosmic ray injection was produced by the same supernova that has deposited 60Fe isotopes in the deep ocean crust.

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Blobrana


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Title: Imprint of a 2 Myr old source on the cosmic ray anisotropy
Author: V. Savchenko, M. Kachelriess, D.V. Semikoz

We study numerically the anisotropy of the cosmic ray (CR) flux emitted by a single source calculating the trajectories of individual CRs. We show that the contribution of a single source to the observed anisotropy is instead determined solely by the fraction the source contributes to the total CR intensity, its age and its distance,and does not depend on the CR energy at late times. Therefore the observation of a constant dipole anisotropy indicates that a single source dominates the CR flux in the corresponding energy range. A natural explanation for the plateau between 2--20 TeV observed in the CR anisotropy is thus the presence of a single, nearby source. For the source age of 2 Myr, as suggested by the explanation of the antiproton and positron data from PAMELA and AMS-02 through a local source [arXiv:astro-ph/1504.06472], we determine the source distance as ~200 pc. Combined with the contribution of the global CR sea calculated in the escape model, we can explain qualitatively the data for the dipole anisotropy. Our results suggest that the assumption of a smooth CR source distribution should be abandoned between 200 GeV and 1 PeV.

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Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Signatures of a two million year old supernova in the spectra of cosmic ray protons, antiprotons and positrons
Author: M. Kachelriess, A. Neronov, D.V. Semikoz

The locally observed cosmic ray spectrum has several puzzling features, such as the excess of positrons and antiprotons above ~20 GeV and the discrepancy in the slopes of the spectra of cosmic ray protons and heavier nuclei in the TeV-PeV energy range. We show that these features are consistently explained by a nearby source which was active ~2 Myr ago and has injected (1-2) x 1050 erg in cosmic rays. The transient nature of the source and its overall energy budget point to the supernova origin of this local cosmic ray source. The age of the supernova suggests that the local cosmic ray injection was produced by the same supernova that has deposited 60Fe isotopes in the deep ocean crust.

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