[Paper Review] Impact of non-thermal particles on the spectral and structural properties of M87

Christian M. Fromm, Alejandro Cruz-Osorio+9 more|arXiv (Cornell University)|Jan 1, 2022

Astrophysical Phenomena and ObservationsPhysics and Astronomy61 references66 citations

TL;DR

This study uses 3D general relativistic magnetohydrodynamic (GRMHD) simulations coupled with radiative transfer to model M87's broad-band spectrum and jet structure. It demonstrates that magnetically arrested disks (MAD) around fast-spinning black holes (a⋆ ≥ 0.5) with a mixture of thermal and non-thermal electrons (kappa distribution) simultaneously reproduce the 86 GHz jet morphology and the full spectral energy distribution from radio to near-infrared, resolving a long-standing degeneracy in jet models.

ABSTRACT

Contains fulltext : 249207.pdf (Publisher’s version ) (Open Access) Contains fulltext : 249207.pdf (Author’s version preprint ) (Closed access)

Motivation & Objective

• To reconcile the observed broad-band spectrum of M87 with its high-resolution jet morphology at 86 GHz.
• To resolve the degeneracy between competing theoretical models of M87's jet by combining spectral and structural constraints.
• To investigate the impact of non-thermal particle distributions on the radiative and morphological properties of the M87 jet.

Proposed method

• 3D general relativistic magnetohydrodynamics (GRMHD) simulations of accretion onto Kerr black holes using the BHAC code.
• Radiative transfer calculations (GRRT) with a hybrid electron distribution function combining thermal and kappa-distributed non-thermal particles.
• A comprehensive parameter survey varying black hole spin (a⋆ = -0.9375 to 0.9375), magnetic flux (SANE vs. MAD), and emission model parameters such as electron temperature ratio and magnetic energy fraction in the kappa model.
• Synthetic images and spectra are convolved with a 0.123 mas × 0.051 mas beam to mimic 86 GHz GMVA observations.
• Model fitting is performed by comparing synthetic spectra and jet collimation profiles to multi-wavelength and VLBI data.
• The R−β model is used to estimate electron temperature from magnetic field and plasma density in the GRMHD output.

Experimental results

Research questions

• RQ1 Can a single model simultaneously reproduce the broad-band spectrum and the 86 GHz jet structure of M87?
• RQ2 What is the role of non-thermal electrons in shaping the spectral energy distribution and jet morphology of M87?
• RQ3 Which accretion model (SANE or MAD) and black hole spin best match the observed spectral and structural properties of M87?
• RQ4 How do variations in electron temperature ratio and magnetic energy fraction in the kappa distribution affect the synthetic observations?
• RQ5 Can the inclusion of jet collimation constraints break the degeneracy between models that fit the spectrum equally well?

Key findings

• The best-fit model combines a magnetically arrested disk (MAD) with a black hole spin of a⋆ ≥ 0.5 and a mixture of thermal and non-thermal electrons with ε = 0.5 (magnetic energy fraction in the kappa model).
• The inclusion of non-thermal particles significantly improves the fit to the near-infrared (NIR) flux and reproduces the extended jet structure observed at 43 GHz and 86 GHz.
• The jet collimation profile from the best-fit MAD model with a⋆ = 0.50 matches the observed parabolic shape from 86 GHz GMVA observations, providing a critical constraint that breaks spectral-only degeneracies.
• The broad-band spectrum is well-fitted across 109 Hz to 1016 Hz regardless of black hole spin or accretion model, but only the MAD model with fast spin satisfies both spectral and structural constraints.
• The model predicts a jet spine with a bulk Lorentz factor of up to 9.9 and a magnetic field strength of ~1.5 × 10² Gauss, consistent with polarisation and VLBI estimates.
• The study demonstrates that combining spectral energy distribution and image structure constraints significantly reduces the degeneracy in jet modeling, favoring high-spin MAD systems.