The Demographics of Sagittarius A* X-ray Flares over 25 Years with Chandra

TL;DR

This paper presents a comprehensive 25-year catalog of Sgr A* X-ray flares observed by Chandra, revealing new flares, spectral correlations, and supporting models of flare mechanisms.

Contribution

It provides the most complete Chandra Sgr A* flare catalog to date, including 18 new flares and analysis of spectral and temporal correlations.

Findings

18 new flares reported, including the second brightest observed by Chandra.

Spectral index increases from ~3 to 2 with flare brightness, indicating spectral hardening.

Correlations between flare duration, fluence, and maximum count rate are reinforced.

Abstract

We present the Chandra 25-year Sagittarius A* (Sgr A*) X-ray flare catalog: a systematic analysis of 6.8 Ms of Sgr A* monitoring spanning the Chandra X-ray Observatory's mission lifetime. This is the most complete Chandra Sgr A* X-ray flare catalog to date, consisting of 100 flares with 2$-$10 keV unabsorbed luminosities ranging from $\sim$ 4$-$575 $\times 10^{33}$ erg s$^{-1}$. 18 flares are reported for the first time, including the second brightest Sgr A* flare observed by Chandra. The expanded dataset supports previous indications of a correlation between X-ray flare hardness and luminosity. Spectral modeling corroborates this finding, showing a change in the X-ray spectral index, from $\Gamma \sim 3$ to 2 with increasing flare brightness. Previously-established correlations between flare duration, fluence, and maximum count rate are strengthened via the greater sample size. These results likely reflect variations in the underlying particle distribution that produce weak and strong flares, and the new catalog serves as a rich archive for ongoing observational and numerical investigations into the physical mechanisms responsible for producing Sgr A*'s X-ray flares.