http://arxiv.org/abs/2010.02826
A recently observed TV bump in the cosmic ray (CR) spectrum, comprising two consecutive breaks, is likely caused by a stellar bow shock. It reaccelerates preexisting CRs, and they diffuse to the Sun along the magnetic field lines. They drive turbulence that self-controls the diffusion and forms the bump. We show that the turbulence has an Iroshnikov-Kraichnan (I-K) spectrum, $k^{-3/2}$, by solving the CR reacceleration and propagation problem analytically. While the ad hoc bump fit requires six parameters, our predicted CR spectrum at the Sun depends on only $two$ parameters, the shock Mach number, $M$, and the bump rigidity $R_{0}$, which absorbs other shock parameters. With $M\approx1.6$ and $R_{0}\approx4.4$ TV, the analytic solution deviates from the data only by $\approx0.08\% $. We rule out turbulence spectra other than the I-K. The analytic solution that depends only on two parameters makes an accidental agreement highly unlikely. The values of $R_{0}$ and $M$ obtained from the fit provide the distance-size ($\zeta_{\rm obs}-l_{\perp}$) relation for the shock: $\zeta_{\rm obs}$(pc) $\sim$ $10^{2}\sqrt{l_{\perp}(\text{pc})}$. Assuming $l_{\perp}=10^{-3}-10^{-2}$ pc, we find the path length along the magnetic field lines of $\zeta_{\rm obs}=3-10$ pc. There are at least two passing stars in this range: the binary Scholz’s Star at 6.8 pc, and a triplet Epsilon Indi at 3.6 pc. Based on their current positions and velocities, we speculate that our Sun is in the wake of the Scholz’s star, while the spectral bump is transmitted by the Epsilon Indi. Given the proximity of this star, the bump appearance may change in a relatively short time.
M. Malkov and I. Moskalenko
Wed, 7 Oct 20
74/76
Comments: 17 pages, 5 figures, pdflatex
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