First mid-infrared detection and modeling of a flare from Sgr A* (2501.07415v1)

Abstract: The time-variable emission from the accretion flow of Sgr A*, the supermassive black hole at the Galactic Center, has long been examined in the radio-to-mm, near-infrared (NIR), and X-ray regimes of the electromagnetic spectrum. However, until now, sensitivity and angular resolution have been insufficient in the crucial mid-infrared (MIR) regime. The MIRI instrument on JWST has changed that, and we report the first MIR detection of Sgr A*. The detection was during a flare that lasted about 40 minutes, a duration similar to NIR and X-ray flares, and the source's spectral index steepened as the flare ended. The steepening suggests synchrotron cooling is an important process for Sgr A*'s variability and implies magnetic field strengths $\sim$40--70 Gauss in the emission zone. Observations at $1.3~\mathrm{mm}$ with the Submillimeter Array revealed a counterpart flare lagging the MIR flare by $\approx$10 minutes. The observations can be self-consistently explained as synchrotron radiation from a single population of gradually cooling high-energy electrons accelerated through (a combination of) magnetic reconnection and/or magnetized turbulence.

• The paper presents the first mid-infrared detection of a Sgr A* flare, identifying a 40-minute event with distinct MIR variability.
• Using JWST’s MIRI, the study applies a synchrotron radiation model to infer magnetic fields of 40–70 Gauss through spectral steepening analysis.
• Multi-wavelength observations, including a 10-minute lagged submillimeter counterpart at 1.3 mm, provide new insights into accretion dynamics and electron cooling processes.

First Mid-Infrared Detection and Modeling of a Flare from Sgr A*

The paper presents the first mid-infrared (MIR) detection of a flare from Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy, leveraging the capabilities of the James Webb Space Telescope’s MIRI instrument. Prior observations of Sgr A* have predominantly focused on various parts of the electromagnetic spectrum, but the mid-infrared had remained largely unexplored mainly due to inadequate sensitivity and resolution of the available instruments. The recent observation from JWST addresses this gap and provides new insights into the nature of Sgr A*'s flaring behavior.

Key Observations and Results

1. Duration and Characteristics of the MIR Flare: The flare observed lasted approximately 40 minutes, displaying durations akin to those seen in the near-infrared (NIR) and X-ray flares of Sgr A*. Notably, the spectral index of the emission steepened as the flare subsided, suggesting significant synchrotron cooling processes at play.
2. Magnetic Field Strength: Through the analysis of the flare’s steepening spectral index, the authors infer the magnetic field strength in the emission region as approximately 40–70 Gauss, indicative of the role magnetic fields play in the variability of Sgr A*'s emissions.
3. Synchrotron Radiation Model: The data supports a model where synchrotron radiation is emitted by a population of high-energy electrons, cooling gradually post acceleration. The synchrotron model not only explains the MIR flare but also predicts associated variability in sub-millimeter wavelengths.
4. Submillimeter Counterpart: Corresponding to the MIR flare, a submillimeter flare was detected lagging by about 10 minutes at 1.3 mm using the Submillimeter Array, providing a multi-wavelength perspective of the event.
5. Absence of X-ray Emission: Despite the MIR flare, no corresponding X-ray flare was detected, which aligns with previous observations indicating that not all flares necessarily exhibit across the spectrum.

Theoretical Implications

The potential synchrotron cooling inferred from these observations suggests that magnetic reconnection or turbulence could serve as viable mechanisms for accelerating electrons to energies sufficient for MIR emission. The high inferred magnetic field strengths challenge earlier models and suggest more dynamic magnetic interactions than previously thought.

Future Research Directions

The implications of this paper open several avenues for future research. With continued observations using JWST and other instruments, one could refine models of accretion disk behavior and magnetohydrodynamic processes within the immediate vicinity of Sgr A*. Additionally, by capturing a wider range of flaring events across different wavelengths, constraints could be placed on the variability patterns and energetic mechanisms.

Furthermore, the observed lag between MIR and submillimeter emissions may provide deeper insights into the geometry and physics of the accretion flow and jet dynamics. These could also contribute to broader theories regarding the interplay of gravitational and magnetic forces around supermassive black holes.

In conclusion, this paper is essential in bridging observational gaps between infrared and (sub-) millimeter regimes and enhancing the understanding of black hole environments. Continued analysis and observational campaigns could result in significant advancements in the paper of black holes and their dynamic environments, contributing to fundamental astrophysical knowledge.