Utilizing cosmic-ray positron and electron observations to probe the averaged properties of Milky Way pulsars

Abstract

Pulsars have long been studied in the electromagnetic spectrum. Their environments are rich in high-energy cosmic-ray electrons and positrons likely enriching the interstellar medium with such particles. In this work we use recent cosmic-ray observations from the AMS-02, CALET and DAMPE collaborations to study the averaged properties of the local Milky Way pulsar population.We perform simulations of the local Milky Way pulsar population, for interstellar medium assumptions in agreement with a range of cosmic-ray nuclei measurements. Each such simulation contains ∼ 10 4 pulsars of unique age, location, initial spin-down power and cosmic-ray electron/positron spectra. We produce more than 7 × 10 3 such Milky Way pulsar simulations. We account for and study i) the pulsars' birth rates and the stochastic nature of their birth, ii) their initial spin-down power distribution, iii) their time evolution in terms of their braking index and characteristic spindown timescale, iv) the fraction of spin-down power going to cosmic-ray electrons and positrons and v) their propagation through the interstellar medium and the Heliosphere. We find that pulsars of ages ∼ 10 5 − 10 7 yr, have a braking index that on average has to be 3 or larger. Given that electromagnetic spectrum observations of young pulsars find braking indices lower than 3, our work provides strong hints that pulsars' braking index increases on average as they age, allowing them to retain some of their rotational energy. Moreover, we find that pulsars have relatively uniform properties as sources of cosmic-ray electrons and positrons in terms of the spectra they produce and likely release O(10%) of their rotational energy to cosmic rays in the ISM. Finally, we find at 12 GeV positrons a spectral feature that suggests a new subpopulation of positron sources contributing at these energies.

Possible Counterpart Signal of the Fermi Bubbles at the Cosmic-Ray Positrons

“…These positrons would reach us, contributing to the local flux. In this paper, we claim a hint of that event leading to a feature in the positron fraction around energies of 12 GeV (see also Cholis & Krommydas 2022b). We find a second feature at 21 GeV, which could come from a more recent inner Galaxy burst event.…”

Constraining the Charge-, Time- and Rigidity-Dependence of Cosmic-Ray Solar Modulation with AMS-02 Observations during Solar Cycle 24

“…In fact, even at rigidities as high as TVs, local sources such as pulsars or recent supernova remnants can have an effect on the spectra on a timescale of only O(10 4 ) years (see e.g. [10,12,18,19,29,58,59]).…”

“…These cosmic-ray spectra have been evaluated by running the publicly available GALPROP code [61][62][63]. In addition, the local ISM positron and electron fluxes come from [29] ("Model I") that relies on the ISM assumptions of model "C" from [60] for the calculation of primary and secondary cosmicray electron and positron fluxes and, through the pres-FIG. 2.…”

Astrophysical and Cosmological Probes of Dark Matter

“…Regardless, AMS-02 measurements remain a highly sensitive probe of dark matter annihilation [215]; for instance, one can search for spectral features associated with the dark matter mass [216,217], although these must be interpreted carefully as astrophysical sources can also generate such features [218,219]. Existing and upcoming cosmic-ray and electromagnetic observations will be used to develop a deeper understanding of the properties of positron sources [220][221][222][223][224], which will further advance the program of probing dark matter with cosmic-rays.…”