Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Razieh Emami, Matthew Liska, Koushik Chatterjee, Geoffrey C. Bower, Wystan Benbow
| Summary:
Recent multi-wavelength observations of M87* citep{2024A&A…692A.140A}
revealed a high-energy $gamma$-ray flare without a corresponding millimeter
counterpart. We present a theoretical polarimetric study to evaluate the
presence and nature of a potential millimeter flare in M87*, using a suite of
general relativistic magnetohydrodynamical simulations with varying black hole
(BH) spins and magnetic field configurations. We find that the emergence of a
millimeter flare is strongly influenced by both spin and magnetic structure,
with limited sensitivity to the electron distribution (thermal vs.
non-thermal). We model the intensity light curve with a damped random walk
(DRW) and compare the characteristic timescale ($tau$) with recent SMA
observations, finding that the simulated $tau$ exceeds observed values by over
an order of magnitude. In a flaring case with BH spin a=+0.5, we identify a
distinct millimeter flare followed by an order-of-magnitude flux drop. All
Stokes parameters show variability near the flare, including a sign reversal in
the electric vector position angle. While most $beta_m$ modes remain stable,
the $EB$-correlation phase is highly sensitive to both the flare peak and
decay. We examine polarimetric signatures in photon sub-rings, focusing on
modes ns=0 and ns=1. The ns=0 signal closely matches the full image, while ns=1
reveals distinct behaviors, highlighting the potential of space VLBI to isolate
sub-ring features. Finally, we analyze the magnetic and velocity field
evolution during the flare, finding that magnetic reconnection weakens during
the flux decay, and the clockwise velocity flow transitions into an
outflow-dominated regime. These results suggest that transient radio
variability near flares encodes key information about black hole spin and
magnetic field structure, offering a novel probe into the physics of active
galactic nuclei.
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