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.