Does the high-energy AMS-02 positron flux originate from the dark matter density spikes around nearby black holes?

TL;DR

The paper investigates whether the high-energy component of the AMS-02 positron flux can originate from dark matter annihilation in density spikes surrounding two nearby black hole X-ray binaries, A0620-00 and XTE J1118+480. By modeling the spike profiles, diffusion and cooling of electrons/positrons, and fitting AMS-02 (and DAMPE) data with a background term plus a DM contribution, the authors identify the $W^+W^-$ annihilation channel with $m_{ m DM}\approx 8000$ GeV as the best-fit scenario, providing a competitive explanation for the high-energy AMS-02 feature and remaining consistent with gamma-ray constraints. The study highlights a novel multi-messenger DM probe involving nearby BH binaries and suggests future cross-checks with neutrino and gamma-ray observations. If validated, this scenario would point to heavy DM and a distinct astrophysical DM environment around compact objects as a source of cosmic-ray positrons.

Abstract

Recent measurements made by the Alpha Magnetic Spectrometer (AMS) have detected accurate positron flux for energy range 1-1000 GeV. The energy spectrum can be best described by two source terms: the low-energy background diffusion term and an unknown high-energy source term. In this article, we discuss the possibility of the emission of positrons originating from dark matter annihilation in two nearby black hole X-ray binaries A0620-00 and XTE J1118+480. We show that the dark matter density spikes around these two black holes can best produce the observed AMS-02 high-energy positron flux due to dark matter annihilation with rest mass $m_{\rm DM} \approx 8000$ GeV via the $W^+W^-$ annihilation channel. This initiates a new proposal to account for the unknown high-energy source term in the AMS-02 positron spectrum.

Figures (3)

• Figure 1: Fitting the AMS-02 positron spectrum with the background emission model plus dark matter annihilation model. The blue and red solid lines represent the best fits for the $W^+W^-$ channel with $m_{\rm DM}=8000$ GeV and $\tau^+\tau^-$ channel with $m_{\rm DM} = 900$ GeV respectively. The dashed lines represent the background emission components and the dotted lines represent the corresponding components originating from A0620-00 and XTE J1118+480 binaries. The data of the AMS-02 positron spectrum are extracted from Aguilar2.
• Figure 2: Fitting the DAMPE spectrum (electron and positron flux) with the background emission model plus dark matter annihilation model. The red solid line represents the total electron and positron flux. The blue and green dashed lines represent the background emission component and the dark matter ($m_{\rm DM}=8000$ GeV) component respectively. The green dotted lines indicate the individual components originating from A0620-00 and XTE J1118+480 binaries. The data are extracted from Ambrosi.
• Figure 3: The red line represents the gamma-ray flux of the dark matter annihilation model following the best-fit scenario ($W^+W^-$ channel with $m_{\rm DM}=8000$ GeV). The error bars indicate the isotropic gamma-ray flux from the Fermi-LAT data extracted from Table 3 of Ackermann2.