English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The $230$\,GHz lightcurves of Sagittarius~A* (Sgr~A*) predicted by generalrelativistic magnetohydrodynamics and ray-tracing (GRRT) models in\citet{2022ApJ...930L..16E} have higher modulation index $M_{\Delta T}$compared to observations. In this series of papers, we explore the origin ofsuch large brightness variability. In this first paper, we performed large GRRTparameter surveys that span from the optically thin to the optically thickregimes, covering $R_{\rm Low}$ from $1$ to $60$. We find, depending on themodel parameters that \emph{i}) increasing $R_{\rm Low}$ to a higher valuecould systematically reduce $M_{\Delta T}$, with $M_{\Delta T}$ consistent withthe observed variability of Sgr~A* in some cases; and \emph{ii}) increasing$R_{\rm Low}$ would make $M_{\Delta T}$ increase to a higher value. Ouranalysis of GRRT image snapshots unravels the large $M_{\Delta T}$ for the$R_{\rm Low} = 1$ models mainly comes from the photon rings. However, secondarycontributions from the accretion flow are also visible depending on the spinparameter. Our work demonstrates the importance of the electron temperatureused for modelling radiatively inefficient accretion flows and places newconstraints on the ion-electron temperature ratio. A more in-depth analysis forunderstanding the dependencies of $M_{\Delta T}$ on $R_{\rm Low}$ will beperformed in subsequent papers.

The $230$ GHz Variability of Numerical Models of Sagittarius A* I. Parameter Surveys on Varying $R_{\rm Low}$