Excesses of cosmic ray spectra from a single nearby source

Growing evidence reveals universal hardening on various cosmic ray spectra, e.g., proton, positron, as well as antiproton fractions. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays ($\mathrm{p}$, ${\mathrm{e}}^{+}$) are produced through the collisions between the primary cosmic-ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of a large number of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary ($\mathrm{p}$, ${\mathrm{e}}^{-}$) and secondary (${\mathrm{e}}^{+}$, $\overline{\mathrm{p}}/\mathrm{p}$) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of the proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction.

Figure 1

The fittings to CR energy spectra, $\mathrm{B}/\mathrm{C}$ (top left), $\overline{\mathrm{p}}/\mathrm{p}$ (top right), proton flux(middle left), positron flux(middle right) and electron flux (bottom left), by DR-A model. For $\mathrm{B}/\mathrm{C}$ ratio, both AMS-02(red) and ACE(1998/01-1999/01)(blue) [72] data are used. The blue and brown dash-dot lines are, respectively, the primary and secondary fluxes from local SNR. The green dash and black solid lines are the background and total flux(or ratio) after solar modulation. The parameters of transport, background and local SNR are reproduced in Table 1.

Figure 2

The fitting to CR energy spectra, $\mathrm{B}/\mathrm{C}$ (top left), $\overline{\mathrm{p}}/\mathrm{p}$ (top right), proton flux(middle left), positron flux(middle right) and electron flux(bottom left), in DR-B model.

Figure 3

The anisotropy of proton under DR-A(left) and DR-B(right) models. The blue dash-dot line is under the assumption of continuous distribution of the sources and steady-state propagation, while the black solid line is the total one when considering the local SNR. The data points are taken from [75, 76].

Figure 4

The anisotropy of electron under DR-A(left) and DR-B(right) models. The blue dash-dot line is under the assumption of continuous distribution of the sources and steady-state propagation, while the black solid line is the total one when considering the local SNR. The black dots are the limits from 1 year Fermi-LAT data [77] and the red line is the recent AMS-02 limits [78].

Figure 5

The blue solid line shows the gamma-ray flux generated during the propagation of the cosmic rays from the local source. The red solid line shows the contribution of the steady-state background cosmic rays. The black dots are the diffuse gamma-ray data measured by Fermi-LAT instrument towards a region of $80°\le l\le 280°$ and $-8°\le b\le 8°$ [84].