Jet-lag in Sgr A*: What size and timing measurements tell us about the central black hole in the Milky Way

Abstract

The black hole at the Galactic Center, Sgr A*, is the prototype of a galactic nucleus at a very low level of activity. Its radio through submm-wave emission is known to come from a region close to the event horizon, however, the source of the emission is still under debate. A successful theory explaining the emission is based on a relativistic jet model scaled down from powerful quasars. We want to test the predictive power of this established jet model against newly available measurements of wavelength-dependent time lags and the size-wavelength structure in Sgr A*. Using all available closure amplitude VLBI data from different groups, we again derived the intrinsic wavelength-dependent size of Sgr A*. This allowed us to calculate the expected frequency-dependent time lags of radio flares, assuming a range of in- and outflow velocities. Moreover, we calculated the time lags expected in the previously published pressure-driven jet model. The predicted lags are then compared to radio monitoring observations at 22, 43, and 350 GHz. The combination of time lags and size measurements imply a mildly relativistic outflow with bulk outflow speeds of gamma*beta ~ 0.5-2. The newly measured time lags are reproduced well by the jet model without any major fine tuning. The results further strengthen the case for the cm-to-mm wave radio emission in Sgr A* as coming from a mildly relativistic jet-like outflow. The combination of radio time lag and VLBI closure amplitude measurements is a powerful new tool for assessing the flow speed and direction in Sgr A*. Future VLBI and time lag measurements over a range of wavelengths will reveal more information about Sgr A*, such as the existence of a jet nozzle, and measure the detailed velocity structure of a relativistic jet near its launching point for the first time.

Latex, 7 pages, accepted for publication in Astronomy & Astrophysics

References in corpus (8)

• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
• Simultaneous Chandra, CSO and VLA Observations of Sgr A*: The Nature of Flaring Activity
• How to hide large scale outflows: size constraints on the jets of Sgr A*
• The Rotation Measure and 3.5mm Polarization of Sgr A*
• Black Hole Shadow Image and Visibility Analysis of Sagittarius A*
• High-resolution Millimeter-VLBI Imaging of Sgr A*

Cited by in corpus (21)

• First Sagittarius A* Event Horizon Telescope Results. III: Imaging of the Galactic Center Supermassive Black Hole
• The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Imaging an Event Horizon: Mitigation of Scattering Toward Sagittarius A*
• Rapid Variability of Sgr A* across the Electromagnetic Spectrum
• ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow
• The X-ray Flux Distribution of Sagittarius A* as Seen by Chandra
• The Intrinsic Two-Dimensional Size of Sagittarius A*
• Asymmetric structure in Sgr A* at 3mm from closure phase measurements with VLBA, GBT and LMT
• Time Variations in the Flux Density of Sgr A* at 230 GHz Detected with ALMA
• The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm
• Simultaneous Monitoring of X-ray and Radio Variability in Sagittarius A*
• No asymmetric outflows from Sagittarius A* during the pericenter passage of the gas cloud G2
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Multi-wavelength torus-jet model for Sgr~A*
• Magnetic flux eruptions at the root of time-lags in low-luminosity AGN
• Short Timescale Evolution of the Polarized Radio Jet during V404 Cygni's 2015 Outburst
• Searching for Radio Outflows from M31* with VLBI Observations
• Variability of Sagittarius A* at 3 GHz on minute-scale with MeerKAT
• A Model For The WMAP Anomalous Ecliptic Plane Signal
• PATOKA: Simulating Electromagnetic Observables of Black Hole Accretion