Simultaneous Monitoring of X-Ray and Radio Variability in Sagittarius A∗

Daniel M. Capellupo, Daryl Haggard, Nicolas Choux, Fred Baganoff, Geoffrey C. Bower, Bill Cotton, Nathalie Degenaar, Jason Dexter, Heino Falcke, P. Chris Fragile, Craig O. Heinke, Casey J. Law, Sera Markoff, Joey Neilsen, Gabriele Ponti, Nanda Rea, Farhad Yusef-Zadeh

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


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 submillimeter and radio wavelengths are limited. Previous work on submillimeter and radio variability hints at a lag between X-ray flares and their candidate submillimeter 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 nine contemporaneous X-ray and radio observations of Sgr A. We detect significant radio variability peaking ≳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 ≲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-rayradio monitoring of Sgr A.

Original languageEnglish (US)
Article number35
JournalAstrophysical Journal
Issue number1
StatePublished - Aug 10 2017


  • Galaxy: center
  • accretion, accretion disks
  • black hole physics
  • radiation mechanisms: non-thermal

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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