Kavli Affiliate: Igor V. Moskalenko
| First 5 Authors: Mikhail A. Malkov, Igor V. Moskalenko, , ,
| Summary:
A recently observed bump in the cosmic ray (CR) spectrum from 0.3–30 TV is
likely caused by a stellar bow shock that reaccelerates emph{preexisting} CRs,
which further propagate to the Sun along the magnetic field lines. Along their
way, these particles generate an Iroshnikov-Kraichnan (I-K) turbulence that
controls their propagation and sustains the bump. {it Ad hoc} fitting of the
bump shape requires six adjustable parameters. Our model requires none, merely
depending on emph{three physical unknowns that we constrain using the fit.}
These are the shock Mach number, $M$, its size, $l_{perp}$, and the distance
to it, $zeta_{text{obs}}$. Altogether, they define the bump rigidity $R_{0}$.
With $M$$approx$1.5–1.6 and $R_{0}$$approx$4.4 TV, the model fits the data
with $approx$$0.08%$ accuracy. The fit critically requires the I-K spectrum
predicted by the model and rules out the alternatives. These fit’s attributes
make an accidental agreement highly unlikely. In turn, $R_{0}$ and $M$ derived
from the fit impose the distance-size %($zeta_{{rm obs}}$$-$$l_{perp}$)
relation on the shock: $zeta_{{rm
obs}}$(pc)$sim$$10^{2}sqrt{l_{perp}(text{pc})}$. For sufficiently large bow
shocks, $l_{perp}$$=$$10^{-3}$$-$$10^{-2}$ pc, we find the distance of
$zeta_{{rm obs}}$$=$3–10 pc. Three promising stars in this range are:
Scholz’s Star at 6.8 pc, Epsilon Indi at 3.6 pc, and Epsilon Eridani at 3.2 pc.
Based on their current positions and velocities, we propose that Epsilon Indi
and Epsilon Eridani can produce the observed spectral bump. Moreover, Epsilon
Eridani’s position is only $sim$$6.7^{circ}$ off of the magnetic field
direction in the solar neighborhood, which also changes the CR arrival
direction distribution. Given the proximity of these stars, the bump appearance
may change in a relatively short time.
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