Fred Baganoff: X-ray Visionary Project: SgrA*

High-res x-ray spectra of Sgr A* & surrounding emission
  • Radio pol obs: most accreting matter doesn't reach event horizon
  • 3 Ms exposure
  • specific roll-angles required because Chandra has no slit
  • detected 6.67 keV Helium-like Fe K-alpha + hi-res rules out 6.4 keV emission model
What mechanism drives Sgr A* flares?
  • what x-ray emission mechanism? Thermal? Compton? Synchro? etc.
  • X-ray/NIR variable
  • mm/radio events weaker, longer timescale, optically thick
  • do mm/radio lead or lag?
  • What determines flare cycle?
  • What triggers flares?
Observations
  • Backgrounds are a big problem
  • Details about order sorting, etc.

Questions

  • Farhad: Discovered a lot of X-ray binaries. Find any sources within 1'?
  • Found the old recurrent ones. Magnetar is new. No new bright ones, searching for faint ones. Vast population of faint variables.
  • Q: Underlying physical mechanism still unknown. Where are we going? How do we figure it out?
  • A: NuStar will help. Very narrow window; can't see optical or UV. This campaign gives more examples.
  • Cornelia: Is anyone working on the diffuse? Nonthermal filament sticks out brightly
  • Yes. Sgr E & F sources. Studying with NuStar team.
  • Q: Can you create images with 3Ms spectra?
  • A: Not much better; the grating reduces raw sensitivity.
  • Q: Dismissed possibility of periodicity. Have you carefully looked? Lomb-Scargle?
  • A: Lots of times with no flaring obvious. But, maybe a lot missed below the noise of the DC signal. Brightest peaks are not periodic. Peaks put into Lomb-Scargle, but not enough data for that. Will look at power spectrum though.

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