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A Multi-messenger Search for a Nearby Microquasar Contributor to the Cosmic Ray Knee

Lin Nie, Hua Yue, Yi-Qing Guo, Si-Ming Liu

TL;DR

This work investigates the origin of the cosmic-ray knee by combining LHAASO gamma-ray observations of microquasars with Galactic CR propagation models and anisotropy data. It demonstrates that known microquasars emitting above 100 TeV contribute negligibly to the knee region, supporting a two-component picture in which sub-PeV CRs arise from SNRs and PeV CRs are dominated by a nearby, possibly unidentified, knee-source. Through joint fits to the proton spectrum and anisotropy, the study localizes a plausible knee-dominant source in the anti-Galactic center direction at a distance of about 2.6 kpc and age around 4.8 Myr, while identifying five binary systems as potential candidates. The results highlight the potential existence of unseen nearby microquasars shaping the knee and guide future observational searches with high-energy gamma-ray instruments.

Abstract

Recently, LHAASO has detected five microquasars with high confidence, which are associated with SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1, respectively. Except for Cygnus X-1, the maximum energies of gamma-ray photons emitted from these sources all exceed 100 TeV, strongly suggesting that microquasars are capable of accelerating cosmic-ray particles to energies above the PeV range. This work investigates the origin of the cosmic-ray knee region based on gamma-ray observational data from the aforementioned sources, combined with cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy observations. Calculations indicate that these known sources contribute negligibly to the cosmic-ray knee region. However, further joint analysis reveals that a single microquasar located in a region approximately on the 2.6 kiloparsec scale in the anti-Galactic center direction can reasonably reproduce the observed cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy features detected near Earth. We propose that this region may host one or several unidentified microquasars or similar systems, whose accelerated cosmic rays could dominate the observational characteristics of the knee region.

A Multi-messenger Search for a Nearby Microquasar Contributor to the Cosmic Ray Knee

TL;DR

This work investigates the origin of the cosmic-ray knee by combining LHAASO gamma-ray observations of microquasars with Galactic CR propagation models and anisotropy data. It demonstrates that known microquasars emitting above 100 TeV contribute negligibly to the knee region, supporting a two-component picture in which sub-PeV CRs arise from SNRs and PeV CRs are dominated by a nearby, possibly unidentified, knee-source. Through joint fits to the proton spectrum and anisotropy, the study localizes a plausible knee-dominant source in the anti-Galactic center direction at a distance of about 2.6 kpc and age around 4.8 Myr, while identifying five binary systems as potential candidates. The results highlight the potential existence of unseen nearby microquasars shaping the knee and guide future observational searches with high-energy gamma-ray instruments.

Abstract

Recently, LHAASO has detected five microquasars with high confidence, which are associated with SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1, respectively. Except for Cygnus X-1, the maximum energies of gamma-ray photons emitted from these sources all exceed 100 TeV, strongly suggesting that microquasars are capable of accelerating cosmic-ray particles to energies above the PeV range. This work investigates the origin of the cosmic-ray knee region based on gamma-ray observational data from the aforementioned sources, combined with cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy observations. Calculations indicate that these known sources contribute negligibly to the cosmic-ray knee region. However, further joint analysis reveals that a single microquasar located in a region approximately on the 2.6 kiloparsec scale in the anti-Galactic center direction can reasonably reproduce the observed cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy features detected near Earth. We propose that this region may host one or several unidentified microquasars or similar systems, whose accelerated cosmic rays could dominate the observational characteristics of the knee region.
Paper Structure (7 sections, 6 equations, 10 figures, 2 tables)

This paper contains 7 sections, 6 equations, 10 figures, 2 tables.

Table of Contents

  1. Introduction
  2. MODEL & METHODOLOGY
  3. Propagation Model of Background CRs
  4. Nearby Sources
  5. Anisotropy of Cosmic Rays
  6. Results and Discussion
  7. Conclusion and Summary

Figures (10)

  • Figure 1: A comparison of the B/C ratio calculated using the CR propagation model with observational data from AMS-02 2017PhRvL.119y1101A, PAMELA 2014ApJ...791...93A, and DAMPE 2022SciBu..67.2162D. The red dashed line indicates the spectrum calculated without considering solar modulation. In this study, the solar modulation potential is consistently assumed to be 550 MeV.
  • Figure 2: The $\gamma$-ray of four microquasars predicted by the model compared with data observed by the LHAASO Cao_2025.
  • Figure 3: The CR proton spectrum is predicted through the CR propagation model and compared with observational data from AMS-02 2015PhRvL.114q1103A, DAMPE 2019SciA....5.3793A, LHAASO Cao_2025 and IceTop 2019PhRvD.100h2002A. The green and red solid lines present background CR component and distribution from the local SNRs, respectively. The dashed lines show the distribution from the SS 433 (blue), V4641 Sgr (yellow), GRS 1915+105 (black), and MAXI J1820+070 (brown), respectively.
  • Figure 4: The energy dependence of the phases of the dipole anisotropies when adding all of the major elements together. The data points are taken from Norikura 1973ICRC....2.1058S, Ottawa 1981ICRC...10..246B, Bolivia 1985PSS...33.1069S, Budapest 1985PSS...33.1069S, Hobart 1985PSS...33.1069S, London 1985PSS...33.1069S, Misato 1985PSS...33.1069S, Socomo 1985PSS...33.1069S, Yakutsk 1985PSS...33.1069S, Liapootah 1995ICRC....4..639M, Matsushiro 1995ICRC....4..648M, Poatina 1995ICRC....4..635F, kamiokande1 1997PhRvD..56...23M, PeakMusala 1975ICRC....2..586G, Norikura 1989NCimC..12..695N, Macro 2003PhRvD..67d2002A, SuperK 2007PhRvD..75f2003G, EAS-TOP 1995ICRC....2..800A1996ApJ...470..501A2009ApJ...692L.130A, Baksan 1987ICRC....2...22A, Milagro 2009ApJ...698.2121A, K-Grande KASCADEAniso2015, IceCube 2010ApJ...718L.194A2012ApJ...746...33A2025ApJ...981..182A, IceTop 2013ApJ...765...55A, AS-$\gamma$2005ApJ...626L..29A2017ApJ...836..153A2015ICRC...34..355A, ARGO 2018ApJ...861...93B, AUGER 2024ApJ...976...48A.
  • Figure 5: The same as Fig.\ref{['alpha']} but for the amplitudes.
  • ...and 5 more figures