Multi-wavelength Observations of Sgr A*. I. 2019 July 18

Abstract

We present and analyze ALMA submillimeter observations from a multi-wavelength campaign of Sgr A* during 18 July 2019. In addition to the submillimeter, we utilize concurrent mid-IR (Spitzer) and X-ray (Chandra) observations. The submillimeter emission lags less than $\delta t\approx 30$ minutes behind the mid-IR data. However, the entire submillimeter flare was not observed, raising the possibility that the time delay is a consequence of incomplete sampling of the light curve. The decay of the submillimeter emission is not consistent with synchrotron cooling. Therefore, we analyze these data adopting an adiabatically expanding synchrotron source that is initially optically thick or thin in the submillimeter, yielding time-delayed or synchronous flaring with the IR, respectively. The time-delayed model is consistent with a plasma blob of radius $0.8R_{\text{S}}$ (Schwarzschild radius), electron power-law index $p=3.5$ ($N(E)\propto E^{-p}$), equipartition magnetic field of $B_{\text{eq}}\approx 90$ Gauss, and expansion velocity $v_{\text{exp}}\approx 0.004c$. The simultaneous emission is fit by a plasma blob of radius $2R_{\text{S}}$, $p=2.5$, $B_{\text{eq}}\approx 27$ Gauss, and $v_{\text{exp}}\approx 0.014c$. Since the submillimeter time delay is not completely unambiguous, we cannot definitively conclude which model better represents the data. This observation presents the best evidence for a unified flaring mechanism between submillimeter and X-ray wavelengths and places significant constraints on the source size and magnetic field strength. We show that concurrent observations at lower frequencies would be able to determine if the flaring emission is initially optically thick or thin in the submillimeter.

arXiv comment9 pages, 5 figures, Accepted to ApJ. Major updates since original submitted version: 1. Correction of mismatching time coordinate systems, 2. Added text discussing time delay error bars, 3. Made text more model-agnostic with respect to time delayed or simultaneous emission. Second revision edits are grammatic in style with updated references

References in corpus (28)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• The Spitzer Space Telescope Mission
• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
• A geometric distance measurement to the Galactic Center black hole with 0.3% uncertainty
• Studies in Astronomical Time Series Analysis. VI. Bayesian Block Representations
• On Uncertainties in Cross-Correlation Lags and the Reality of Wavelength-Dependent Continuum Lags in Active Galactic Nuclei
• The Chandra Source Catalog
• Bayesian Blocks, A New Method to Analyze Structure in Photon Counting Data
• Line derived infrared extinction towards the Galactic Center
• Evidence for X-ray synchrotron emission from simultaneous mid-IR to X-ray observations of a strong Sgr A* flare
• Polarimetry of near-infrared flares from Sagittarius A*
• A Chandra/HETGS Census of X-ray Variability From Sgr A* During 2012
• First Simultaneous NIR/X-ray Detection of a Flare from SgrA*
• Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
• A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• Variability Timescale and Spectral Index of Sgr A* in the Near Infrared: Approximate Bayesian Computation Analysis of the Variability of the Closest Supermassive Black Hole
• An 8 hour characteristic time-scale in submillimetre light curves of Sagittarius A*
• Simultaneous NIR/sub-mm observation of flare emission from SgrA*
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• Improved AGN light curve analysis with the z-transformed discrete correlation function
• Modeling mm- to X-ray flare emission from SgrA*
• Simultaneous X-ray and Infrared Observations of Sagittarius A*'s Variability
• Spitzer/IRAC Observations of the Variability of Sgr A* and the Object G2 at 4.5 microns
• Multiwavelength Light Curves of Two Remarkable Sagittarius A* Flares
• Multiwavelength study of the flaring activity of Sgr A* in 2014 February-April
• Simultaneous Monitoring of X-ray and Radio Variability in Sagittarius A*

Cited by in corpus (3)

• Observational signatures of hot spots orbiting horizonless objects
• General relativistic effects and the near-infrared and X-ray variability of Sgr A* I
• Nonthermal hotspot orbiting the supermassive black hole Sgr A*