AMS02 results support the secondary origin of cosmic ray positrons

TL;DR

The AMS02 positron data aligns with secondary production models, suggesting positrons originate from cosmic ray interactions in the galaxy rather than primary sources like pulsars or dark matter.

Contribution

This study demonstrates that recent AMS02 measurements support secondary origin models for cosmic ray positrons, challenging the need for primary sources.

Findings

Positron fraction saturates the secondary production upper bound.

Implied cosmic ray propagation time is less than a million years.

Average interstellar matter density is about 1/cc at 300 GV rigidity.

Abstract

We show that the recent AMS02 positron fraction measurement is consistent with a secondary origin for positrons, and does not require additional primary sources such as pulsars or dark matter. The measured positron fraction at high energy saturates the previously predicted upper bound for secondary production (Katz et al 2009), obtained by neglecting radiative losses. This coincidence, which will be further tested by upcoming AMS02 data at higher energy, is a compelling indication for a secondary source. Within the secondary model the AMS02 data imply a cosmic ray propagation time in the Galaxy of < Myr and an average traversed interstellar matter density of order 1/cc, comparable to the density of the Milky Way gaseous disk, at a rigidity of 300 GV.