Multimessenger Emission from Very-High-Energy Black Hole-Jet Systems in the Milky Way

TL;DR

This work develops a multimessenger framework to test high-energy particle acceleration in Galactic microquasars identified by LHAASO as sources of $>100$ TeV gamma rays. A transport-based phenomenological model is employed, accounting for acceleration at jets and wind shocks within regions of size $R$ and magnetic field $B$, to compute electron and proton populations and their radiative and hadronic outputs that reproduce X-ray, gamma-ray, and TeV data for SS 433, V4641 Sgr, and GRS 1915+105. The analysis finds that hadronic $pp$ interactions in relatively low-density environments (n_p ~ 1–10 cm$^{-3}$) are needed to produce the $>100$ TeV tail, while leptonic emission struggles to reach those energies due to synchrotron cooling; neutrino production tracks the hadronic component and is generally below current IceCube-Gen2 horizons, though next-generation networks could detect signals from favorable wind-region conditions, notably for V4641 Sgr. The study underscores the importance of multimessenger observations to reveal hadronic acceleration in Galactic PeVatrons and informs strategies for future neutrino-search campaigns.

Abstract

Microquasars, compact binary systems with an accreting stellar-mass black hole or neutron star, are promising candidates for high-energy particle acceleration. Recently, the LHAASO collaboration reported on the detection of $>100$ TeV $γ$-ray emission from five microquasars, suggesting that these sources are efficient particle accelerators. In microquasars, high-energy $γ$-rays can be produced in large-scale jets or winds. In this work, we explore the X-ray, $γ$-ray and neutrino emission from SS 433, V4641 Sgr and GRS 1905+105. We consider leptonic and hadronic scenarios to explain the spectra observed by LHAASO and other high-energy $γ$-ray detectors. We estimate the neutrino flux associated with the hadronic component and investigate the detectability of neutrinos from these sources in current and future neutrino telescopes. We find that among the three sources, V4641 Sgr has the best prospects of observation with a combined next-generation neutrino telescopes.

Figures (7)

• Figure 1: Schematic of the model used in this study. Particles are accelerated via diffusive shock acceleration, both in the jet and in the isotropic wind. Electrons interact with the CMB photons and upscatter them to TeV energies via IC.
• Figure 2: Multimessenger emission from the jet in the eastern lobe of SS 433. The total photon spectrum is shown as a thick black curve, and the leptonic (hadronic) component as a crimson (blue) thin curve. The dashed line corresponds to the predicted muon-neutrino spectrum. The eastern lobe electromagnetic measurements from XMM-Newton (magenta triangles) Brinkmann:2006zt, RXTE (dark green stars) Safi-Harb_1999, Fermi (orange diamonds, 95% upper limits and $1\sigma$ bars) Fang:2020tcd, HAWC (light green squares) HAWC:2024ysp, H.E.S.S. (purple pentagons) HESS:2024rlh and LHAASO (golden circles) LHAASO:2024psv are shown.
• Figure 3: ${\gamma}$-ray and neutrino emission associated with the SS 433 extended region identified by LHAASO. The purple (blue) curves correspond to the combined jet and wind (only wind) ${\gamma}$-rays . The dashed lines are the expected $\nu_\mu+\bar{\nu}_\mu$ fluxes. LHAASO observations are shown as golden circles LHAASO:2024psv.
• Figure 4: Top panel: Multimessenger emission from the XRISM X-ray source region in V4641 Sgr. Fermi-LAT Neronov:2024ycp, HAWC HAWC:2024ysp and LHAASO LHAASO:2024psv are shown as orange diamonds, green squares and golden circles, respectively. XRISM X-ray band shown as the shaded purple region Suzuki:2024rzc. and HAWC data were scaled to the XRISM source region size, as done in Suzuki:2024rzc. Bottom panel: Same as left panel, but assuming the HAWC source region instead.
• Figure 5: Multimessenger emission from GRS 1915+105. Fermi-LAT Marti-Devesa:2024otf and LHAASO LHAASO:2024psv are shown as orange diamonds and golden circles, respectively.