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Abstract The central 5 pc of our Galactic center is rich in various molecular tracers. The region is observed to be hot, highly ionized, and volatile, resulting in complex chemistry and kinematics. Countless molecular observations of the central region orbiting the central supermassive black hole Sgr A^*have revealed a stable grouping of clouds with a disklike structure known as the circumnuclear disk (CND) orbiting Sgr A^*between 1.5 and 3 pc. The CND houses the densest population of gas outside the ionized streams in the minispiral falling onto Sgr A^*. However, the small-scale kinematics of the clouds and gas are poorly understood in this region. In this paper, we report single-dish SiO (1–0) observations of the central 5 pc surrounding Sgr A^*taken with the Green Bank Telescope. Most of the SiO (1–0) traces the Southern Streamer and Sgr A East—neither of which are associated with the CND. However, one region in the CND, known as the Northeast (NE) Arm, shows high-intensity SiO emission unlike in the rest of the CND, indicating the NE Arm as a candidate region of either cloud–cloud collision or early star formation. Further high-resolution observations of the region are needed to distinguish between the two scenarios. 

Abstract We present the first results of JWST Cycle 1 and 2 observations of Sgr A* using NIRCam taken simultaneously at 2.1 and 4.8μm for a total of ∼48 hr over seven different epochs in 2023 and 2024. We find correlated variability at 2.1 and 4.8μm in all epochs, continual short-timescale (a few seconds) variability, and epoch-to-epoch variable emission implying long-term (∼days to months) variability of Sgr A*. A highlight of this analysis is the evidence for subminute, horizon-scale time variability of Sgr A*, probing inner accretion disk size scales. The power spectra of the light curves in each observing epoch also indicate long-term variable emission. With continuous observations, JWST data suggest that the flux of Sgr A* is fluctuating constantly. The flux density correlation exhibits a distinct break in the slope at ∼3 mJy at 2.1μm. The analysis indicates two different processes contributing to the variability of Sgr A*. Brighter emission trends toward shallower spectral indices than the fainter emission. Cross-correlation of the light curves indicates for the first time a time delay of 3–40 s in the 4.8μm variability with respect to 2.1μm. This phase shift leads to loops in plots of flux density versus 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 light curves with a direct estimate of the magnetic field strengths in the range between 40 and 90 G and an upper cutoff energy,E_c, between 420 and 720 MeV. 

Context.The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) facilities (from radio toγ-ray energies) took part in the second M87 EHT campaign. Aims.The goal of this extensive MWL campaign was to better understand the physics of the accreting black hole M87*, the relationship between the inflow and inner jets, and the high-energy particle acceleration. Understanding the complex astrophysics is also a necessary first step towards performing further tests of general relativity. Methods.The MWL campaign took place in April 2018, overlapping with the EHT M87* observations. We present a new, contemporaneous spectral energy distribution (SED) ranging from radio to very high-energy (VHE)γ-rays as well as details of the individual observations and light curves. We also conducted phenomenological modelling to investigate the basic source properties. Results.We present the first VHEγ-ray flare from M87 detected since 2010. The flux above 350 GeV more than doubled within a period of ≈36 hours. We find that the X-ray flux is enhanced by about a factor of two compared to 2017, while the radio and millimetre core fluxes are consistent between 2017 and 2018. We detect evidence for a monotonically increasing jet position angle that corresponds to variations in the bright spot of the EHT image. Conclusions.Our results show the value of continued MWL monitoring together with precision imaging for addressing the origins of high-energy particle acceleration. While we cannot currently pinpoint the precise location where such acceleration takes place, the new VHEγ-ray flare already presents a challenge to simple one-zone leptonic emission model approaches, and it emphasises the need for combined image and spectral modelling.