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Arxiv: Non-stop Variability of Sgr A* using JWST at 2.1 and 4.8 micron Wavelengths: Evidence for Distinct Populations of Faint and Bright Variable Emission Published: 1/7/2025 9:00:29 PM Updated: 1/7/2025 9:00:29 PM

Paper abstract: We present first results of JWST Cycle 1 and 2 observations of Sgr A* usingNIRCam taken simultaneously at 2.1 and 4.8 micron for a total of ~48 hours overseven different epochs in 2023 and 2024. We find correlated variability at 2.1and 4.8 micron in all epochs, continual short-time scale (a few seconds)variability and epoch-to-epoch variable emission implying long-term ( ~days tomonths) variability of Sgr A*. A highlight of this analysis is the evidence forsub-minute, horizon-scale time variability of Sgr A*, probing inner accretiondisk size scales. The power spectra of the light curves in each observing epochalso indicate long-term variable emission. With continuous observations, JWSTdata suggest that the flux of Sgr A* is fluctuating constantly. The fluxdensity correlation exhibits a distinct break in the slope at ~3 mJy at 2.1micron. The analysis indicates two different processes contributing to thevariability of Sgr A*. Brighter emission trends towards shallower spectralindices than the fainter emission. Cross correlation of the light curvesindicates for the first time, a time delay of 3 - 40 sec in the 4.8 micronvariability with respect to 2.1 micron. This phase shift leads to loops inplots of flux density vs spectral index as the emission rises and falls.Modeling suggests that the synchrotron emission from the evolving,age-stratified electron population reproduces the shape of the observed lightcurves with a direct estimate of the magnetic field strengths in the rangebetween 40-90 G, and upper cutoff energy, E_c, between 420 and 720 MeV.