Multiwavelength Light Curves of Two Remarkable Sagittarius A* Flares

TL;DR

This study reports two unusual multiwavelength flares from Sgr A* that challenge existing models of black hole emission mechanisms, highlighting the need for ongoing coordinated observations to better understand SMBH variability.

Contribution

The paper presents the first observations of two atypical Sgr A* flares with unusual timing sequences, questioning previous assumptions about emission mechanisms.

Findings

First evidence of coeval NIR and submm flux increases.

First example of submm/X-ray/NIR flux increases within ~1 hour.

Flares challenge existing models of SMBH variability.

Abstract

Sgr A*, the supermassive black hole (SMBH) at the center of our Milky Way Galaxy, is known to be a variable source of X-ray, near-infrared (NIR), and submillimeter (submm) radiation and therefore a prime candidate to study the electromagnetic radiation generated by mass accretion flow onto a black hole and/or a related jet. Disentangling the power source and emission mechanisms of this variability is a central challenge to our understanding of accretion flows around SMBHs. Simultaneous multiwavelength observations of the flux variations and their time correlations can play an important role in obtaining a better understanding of possible emission mechanisms and their origin. This paper presents observations of two flares that both apparently violate the previously established patterns in the relative timing of submm/NIR/X-ray flares from Sgr A*. One of these events provides the first evidence of coeval structure between NIR and submm flux increases, while the second event is the first example of the sequence of submm/X-ray/NIR flux increases all occurring within ~1 hr. Each of these two events appears to upend assumptions that have been the basis of some analytic models of flaring in Sgr A*. However, it cannot be ruled out that these events, even though unusual, were just coincidental. These observations demonstrate that we do not fully understand the origin of the multiwavelength variability of Sgr A*, and show that there is a continued and important need for long-term, coordinated, and precise multiwavelength observations of Sgr A* to characterize the full range of variability behavior.