Improved analysis of time delays between radio wavelengths and X-ray of Sgr A* flares in the shock oscillation model
Year: 2026
Type: article
Abstract: ABSTRACT We present an improved analysis of the time delays between radio and X-ray flares from the supermassive black hole Sagittarius A*, extending our previous shock oscillation model by incorporating Compton scattering. Our simulations predict the following delay times: 1–4 h between X-ray and radio flares, 20–40 min and 0.5–1 h between 334 GHz and 4.5 μm and 2–8 keV flares, and 7–20 min and 0.5–1 h between 22–43 and 350 GHz radio flares. These findings are in good agreement with recent observations. The delay time between the radio emissions (synchrotron) and X-ray emissions (bremsstrahlung) is interpreted as the transit time for sound waves travelling from the central core near the event horizon to the location of the oscillating shock. Additionally, the delay time observed between different radio wavelengths corresponds to the transit time of sound waves moving between the frequency-dependent effective radii $R_{\rm eff}(\nu)$, where the optical thickness $\tau _{\nu }(R)$ at frequency $\nu$ equals one on the surface of the accretion disc. The X-ray emission and the radio emission at lower frequencies peak later than the radio emission at higher frequencies. This delay occurs because the acoustic perturbations created by synchrotron emission peak near the event horizon and then expand outward. Conversely, an inverse delay happens when the acoustic waves generated by the upstream shock wave travel towards the event horizon. The predicted delay times from this interpretation qualitatively match the numerical results obtained in simulations.
Authors: Ramiz Aktar, Toru Okuda, Chandra B Singh
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
OpenAlex ID: W7221073215