Simultaneous Monitoring of X-ray and Radio Variability in Sagittarius A*

Abstract

Monitoring of Sagittarius A* from X-ray to radio wavelengths has revealed structured variability --- including X-ray flares --- but it is challenging to establish correlations between them. Most studies have focused on variability in the X-ray and infrared, where variations are often simultaneous, and because long time series at sub-millimeter and radio wavelengths are limited. Previous work on sub-mm and radio variability hints at a lag between X-ray flares and their candidate sub-millimeter or radio counterparts, with the long wavelength data lagging the X-ray. However, there is only one published time lag between an X-ray flare and a possible radio counterpart. Here we report 9 contemporaneous X-ray and radio observations of Sgr A*. We detect significant radio variability peaking $\gtrsim$176 minutes after the brightest X-ray flare ever detected from Sgr A*. We also report other potentially associated X-ray and radio variability, with the radio peaks appearing $\lesssim$80 minutes after these weaker X-ray flares. Taken at face value, these results suggest that stronger X-ray flares lead to longer time lags in the radio. However, we also test the possibility that the variability at X-ray and radio wavelengths is not temporally correlated. We cross-correlate data from mismatched X-ray and radio epochs and obtain comparable correlations to the matched data. Hence, we find no overall statistical evidence that X-ray flares and radio variability are correlated, underscoring a need for more simultaneous, long duration X-ray--radio monitoring of Sgr A*.

Accepted for publication in ApJ

References in corpus (16)

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• The Galactic Center cloud G2 and its gas streamer
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• Jet-lag in Sgr A*: What size and timing measurements tell us about the central black hole in the Milky Way
• ALMA and VLA measurements of frequency-dependent time lags in Sagittarius A*: evidence for a relativistic outflow
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Cited by in corpus (10)

• First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multi-wavelength Observations, Data Processing, and Calibration
• Millimeter light curves of Sagittarius A* observed during the 2017 Event Horizon Telescope campaign
• Radio Frequency Timing Analysis of the Compact Jet in the Black Hole X-ray Binary Cygnus X-1
• Constraining a companion of the galactic center black hole, Sgr A*
• Multi-wavelength Observations of Sgr A*. I. 2019 July 18
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Radiative shock oscillation model for the long-term flares of Sgr A*
• Time delays between radio and X-ray and between narrow radio bands of Sgr A* flares in the shock oscillation model
• Visible shapes of black holes M87* and SgrA*
• Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign