# Simultaneous X-ray and Infrared Observations of Sagittarius A*'s Variability

## TL;DR

This study presents the longest simultaneous X-ray and infrared observations of Sagittarius A*, revealing potential time lag in flares that constrains models of the black hole's accretion and emission processes.

## Contribution

It provides the first extensive dataset of simultaneous IR and X-ray observations of Sgr A*, analyzing flare timing and correlation with unprecedented detail.

## Key findings

- X-ray flares may lead IR flares by 10-20 minutes
- Flares are statistically consistent with being simultaneous
- Longer observations are needed to better constrain flare timing

## Abstract

Emission from Sgr A* is highly variable at both X-ray and infrared (IR) wavelengths. Observations over the last ~20 years have revealed X-ray flares that rise above a quiescent thermal background about once per day, while faint X-ray flares from Sgr A* are undetectable below the constant thermal emission. In contrast, the IR emission of Sgr A* is observed to be continuously variable. Recently, simultaneous observations have indicated a rise in IR flux density around the same time as every distinct X-ray flare, while the opposite is not always true (peaks in the IR emission may not be coincident with an X-ray flare). Characterizing the behaviour of these simultaneous X-ray/IR events and measuring any time lag between them can constrain models of Sgr A*'s accretion flow and the flare emission mechanism. Using 100+ hours of data from a coordinated campaign between the Spitzer Space Telescope and the Chandra X-ray Observatory, we present results of the longest simultaneous IR and X-ray observations of Sgr A* taken to date. The cross-correlation between the IR and X-ray light curves in this unprecedented dataset, which includes four modest X-ray/IR flares, indicates that flaring in the X-ray may lead the IR by approximately 10-20 minutes with 68% confidence. However, the 99.7% confidence interval on the time-lag also includes zero, i.e., the flaring remains statistically consistent with simultaneity. Long duration and simultaneous multiwavelength observations of additional bright flares will improve our ability to constrain the flare timing characteristics and emission mechanisms, and must be a priority for Galactic Center observing campaigns.