Dipole anisotropy in cosmic electrons and positrons: inspection on local sources

Abstract

The cosmic electrons and positrons have been measured with unprecedented statistics up to several hundreds GeV, thus permitting to explore the role that close single sources can have in shaping the flux at different energies. In the present analysis, we consider electrons and positrons in cosmic rays to be produced by spallations of hadron fluxes with the interstellar medium, by a smooth Supernova Remnant (SNR) population, by all the ATNF catalog pulsars, and by few discrete, local SNRs. We test several source models on the e + + e − and e + AMS-02 flux data. For the configurations compatible with the data, we compute the dipole anisotropy in e + + e − , e + , e + /e − from single sources. Our study includes a dedicated analysis to the Vela SNR. We show that Fermi-LAT present data on dipole anisotropy of e + + e − start to explore some of the models for the Vela SNR selected by AMS-02 flux data. We also investigate how the observed anisotropy could result from a combination of local sources. Our analysis shows that the search of anisotropy in the lepton fluxes up to TeV energies can be an interesting tool for the inspection of properties of close SNRs, complementary to the high precision flux data.

Constraining the emission of cosmic electrons from supernova remnants with flux, dipole anisotropy and radio data

“…The model used for the sources and for the propagation of CRE is based on [6], to which we address for any detail (see also [7]). Supernova Remnants (SNRs) are considered the best candidate to accelerate Galactic CR thought diffuse shock acceleration, and are included in our model as sources of e − .…”

“…As for the propagation parameters (δ , K 0 , L), the results of the recent analysis of B/C AMS-02 data in [8] (Kappl+15) and [9] (Genolini+15) are used. As described in [6], a smooth distribution of SNRs following a radial profile taken from [10] (G15) is considered, as well as single SNRs taken from the Green catalog [11]. When the single SNRs with distance d < R cut are inserted in the model, the smooth distribution is cutted to become the far SNRs contribution for R = |r − r | < R cut .…”

“…An additional observable that we use to test our models is the dipole anisotropy of the CRE fluxes (see [6] and references therein). In fact, when a single or few single sources are introduced to explain an important part of the CRE fluxes, a dipole anisotropy may arise in the observed fluxes.…”

“…The λ (E, E s ) is the typical propagation scale (see Eq. 2.11 of [6]) and ψ tot e + +e − (E) refers to the total e + + e − number density, including both the contributions from isotropic smooth populations as well as single sources. As discussed in [6], we compute anisotropy predictions only for the models compatible with CRE data, and we then compare our results to the anisotropy upper limits.…”

“…[14,6] and references therein). The smooth distribution of SNRs is thus considered here with a radial cut of R cut = 0.7 kpc, becoming the far SNRs component.…”