White dwarf pulsars as possible cosmic ray electron-positron factories

Abstract

We suggest that white dwarf (WD) pulsars can compete with neutron star (NS) pulsars for producing the excesses of cosmic ray electrons and positrons (e[±]) observed by the PAMELA, ATIC/PPB-BETS, Fermi, and H.E.S.S. experiments. A merger of two WDs leads to a rapidly spinning WD with a rotational energy (∼10[50] erg) comparable to the NS case. The birth rate (∼10[-2]–10[-3]/yr/galaxy) is also similar, providing the right energy budget for the cosmic ray e±. Applying the NS theory, we suggest that the WD pulsars can in principle produce e[±] up to ∼10 TeV. In contrast to the NS model, the adiabatic and radiative energy losses of e[±] are negligible since their injection continues after the expansion of the pulsar wind nebula, and hence it is enough that a fraction ∼1% of WDs are magnetized (∼10[7]–10[9] G) as observed. The long activity also increases the number of nearby sources (∼100), which reduces the Poisson fluctuation in the flux. The WD pulsars could dominate the quickly cooling e[±] above TeV energy as a second spectral bump or even surpass the NS pulsars in the observing energy range ∼10 GeV–1 TeV, providing a background for the dark matter signals and a nice target for the future AMS-02, CALET, and CTA experiment.