Galactic molecular clouds as sources of secondary positrons

TL;DR

This paper models the contribution of Galactic Molecular Clouds to the observed positron spectrum on Earth, incorporating recent GMC data, cosmic ray interactions, and reacceleration effects, successfully explaining observations between 1 and 1000 GeV.

Contribution

It introduces a comprehensive model including recent GMC surveys and reacceleration effects to explain the positron spectrum observed on Earth.

Findings

GMCs significantly contribute to the positron spectrum.

Reacceleration in GMCs produces a hardened positron component.

Model matches observed data from 1 to 1000 GeV.

Abstract

Secondary positrons produced inside Galactic Molecular Clouds (GMCs) can significantly contribute to the observed positron spectrum on Earth. Multi-wavelength data of GMCs are particularly useful in building this model. A very recent survey implemented the optical/IR dust extinction measurements to trace 567 GMCs within 4 kpc of Earth, residing in the Galactic plane. We use the updated catalog of GMCs reported in recent papers, distributed in the Galactic plane, to find the secondary positrons produced in them in interactions of cosmic rays with molecular hydrogen. Moreover, by analyzing the \textit{Fermi}-LAT data, new GMCs have been discovered near the Galactic plane. We also include some of these GMCs closest to the Earth, where cosmic ray interactions produce secondaries. It has been speculated earlier that cosmic rays may be reaccelerated in some GMCs. We select 7 GMCs out of 567 GMCs recently reported, within 4 kpc of Earth, where reacceleration due to magnetized turbulence is assumed. We include a hardened component of secondary positrons produced from the interaction of reaccelerated CRs in those 7 GMCs. We use publicly available code \texttt{DRAGON} for our simulation setup to study CR propagation in the Galaxy and show that the observed positron spectrum can be well explained in the energy range of 1 to 1000 GeV by our self-consistent model.