CosRayMC: a global fitting method in studying the properties of the new sources of cosmic e$^{\pm}$ excesses

TL;DR

This paper introduces CosRayMC, a Markov Chain Monte Carlo method using GALPROP to analyze cosmic ray data, demonstrating the necessity of extra sources like pulsars or dark matter to explain observed excesses.

Contribution

Developed CosRayMC, a novel MCMC-based fitting tool for cosmic ray data, providing constraints on source models and dark matter properties.

Findings

Extra sources significantly improve data fit (reduced chi-squared from 3.68 to 0.83).

Both pulsar and dark matter models fit the data similarly well.

Dark matter annihilation into quarks is constrained to less than 0.5% branching ratio.

Abstract

Recently PAMELA collaboration published the cosmic nuclei and electron spectra with high precision, together with the cosmic antiproton data updated, and the Fermi-LAT collaboration also updated the measurement of the total $e^+e^-$ spectrum to lower energies. In this paper we develop a Markov Chain Monte Carlo (MCMC) package {\it CosRayMC}, based on the GALPROP cosmic ray propagation model to study the implications of these new data. It is found that if only the background electrons and secondary positrons are considered, the fit is very bad with $\chi_{\rm red}^2 \approx 3.68$. Taking into account the extra $e^+e^-$ sources of pulsars or dark matter annihilation we can give much better fit to these data, with the minimum $\chi_{\rm red}^2 \approx 0.83$. This means the extra sources are necessary with a very high significance in order to fit the data. However, the data show little difference between pulsar and dark matter scenarios. Both the background and extra source parameters are well constrained with this MCMC method. Including the antiproton data, we further constrain the branching ratio of dark matter annihilation into quarks $B_q<0.5%$ at $2\sigma$ confidence level. The possible systematical uncertainties of the present study are discussed.