Vela-X as main contributor to the electron and positron spectra at energy above 100 GeV

Abstract

The precise measurements of the electron plus positron spectra, in the energy range from 0.5 GeV up to 1 TeV, were published by the AMS-02 collaboration. We focus the attention above 10 GeV where the solar modulation effects are negligible. The differences between these data and the "classical" Local Interstellar Spectra, obtained using optimized GALPROP parameters, show an extra contribution suggesting an equal amount for both electrons and positrons. Thus, they would be generated by a pair production process from the same source. We studied the contribution from Pulsar Wind Nebulae starting from the photon spectrum (due to synchrotron and inverse Compton processes) detected by gamma-ray telescopes. A diffusion model is applied from the source up to the Solar System and the propagated spectra are compared with the AMS-02 data. Above 100 GeV, Vela-X is the main candidate to contribute to the observed excess, while, below 100 GeV, more aged pulsars like Monogem give a higher contribution. An estimation on the degree of anisotropy from these sources is also presented.

Propagation of cosmic rays in heliosphere: The HelMod model

“…The increased performance of on-board spectrometers was and is currently enabling to enhance the accuracy of the observed spectra. Thus, it was opening the way to a better understanding of processes related to the transport of GCRs through the Heliosphere -the so-called modulation effect -and, ultimately, to the capability a) to unveil local interstellar spectra (LIS) of GCR species (e.g., see Potgieter, 2014, 2016;Della Torre et al, 2017a;Boschini et al, 2017, and also references therein), b) to investigate their generation, acceleration and diffusion process within the Milky Way (e.g., see Boella et al, 1998;Strong et al, 2007;Evoli et al, 2008;Putze et al, 2009), and, in turn, c) to possibly untangle features due to new physics -i.e., dark matter (e.g., see Bottino et al, 1998;Cirelli and Cline, 2010;Ibarra et al, 2010;Salati, 2011;Weniger, 2011, and references therein) -or additional astrophysical sources so far not taken into account (e.g., see Chang * Corresponding author Email address: piergiorgio.rancoita@mib.infn.it (P. G. Rancoita) Abdo et al, 2009;Adriani et al, 2009a;Cernuda, 2011;Mertsch and Sarkar, 2011;Della Torre et al, 2015;Rozza et al, 2015, and references therein).…”

Pulsar Wind Nebulae as a source of the observed electron and positron excess at high energy: The case of Vela-X

“…If no other source is missed, we expect a dipole anisotropy above 100 GeV centered in the direction of Vela. At 200 GeV, the dipole anisotropy for electrons plus positrons from Vela-X is expected to be of the order of ∼2% (Rozza et al, 2015) not yet excluded by the FERMI experiment (Ackermann et al, 2010). Conversely, at lower energy, several sources can contribute to the electron and positron spectra, but the angular distribution of all these sources should be more isotropic.…”

Cosmic rays: direct measurements

“…11(a)). In [82], a better fit to the AMS e + + e − spectrum above 100 GeV is obtained by adding a contribution from the pulsars Vela-X and Monogem to the standard local interstellar spectrum calculated with GALPROP. However, the uncertainties on CR propagation parameters significantly affect the predicted positron rise for both the scenarios [83], thus strongly limiting at the moment the possibility to ascertain the origin of the excess.…”