1. What Are the Faint X-ray Transients Near the Galactic Center? Michael Muno (UCLA/Hubble Fellow) Fred Baganoff (MIT), Eric Pfahl (UVa), Niel Brandt, Gordon Garmire (Penn State) Mark Morris, Andrea Ghez, Jessica Lu, Seth Hornstein (UCLA)

2. Five Years of Chandra Observations of the Galactic Center Sgr A* 5 pc Galactic Plane 0.1% of the Galactic stellar mass!

3. X-ray Sources within 25 pc of Sgr A* Previous wide-field surveys were only sensitive to L X >10 36 erg s - 1. Most of the Chandra X-ray sources have L X =10 31 to 10 33 erg s -1. These are likely to be CVs. Seven transient X-ray sources have L X >10 34 to 10 36 erg s -1. These are a bit unexpected... Sgr A* 5 pc

4. X-ray Sources within 25 pc of Sgr A* Previous wide-field surveys were only sensitive to L X >10 36 erg s - 1. Most of the Chandra X-ray sources have L X =10 31 to 10 33 erg s -1. These are likely to be CVs. Seven transient X-ray sources have L X >10 34 to 10 36 erg s -1. These are a bit unexpected... Sgr A* New Transient 5 pc

5. Your Standard Transient X-ray Source Most bright, transient X-ray sources are accreting black holes and neutron stars. When accretion occurs at low rates, the disk tends to be unstable, producing outbursts with L X >10 37 erg s -1. One Solar Radius Image creates with binsim, by Rob Hynes Location of Compact Object

6. Thermonuclear Bursts from a Neutron Star Low-Mass X-ray Binary Sgr A* New Transient 5 pc An X-ray burst lasting 100 s was produced by unstable He burning on the neutron star.

7. Another LMXB (0.1 pc from Sgr A*) with Periodic Eclipses The X-ray light curve displays partial eclipses at the 8 hour orbital period. Infrared images reveal no infrared companion with K<15, ruling out a high-mass star. Muno et al. (2005b) To Sgr A* (0.1 pc)

8. Jets Carry Away Much of the Accretion Energy A surprisingly bright (90 mJy at 43 GHz) pair of radio lobes was also seen. They were stationary, and probably formed where the jet impacted the ISM. The minimum power required to produce the lobes was 10 37 erg s -1, similar to L X. VLA 8.4 GHz Transient Sgr A* Bower, Yusef-Zadeh, Roberts et al. 2005

9. Other Transients also have Unusual Properties Transient outbursts last anywhere from less than a month, to the full five years. The long, slow transient to the left has a soft spectrum reminiscent of transient magnetars.

10. Making Progress on Faint X-ray Transients We need better X-ray coverage, to identify new examples and to measure outburst time scales and spectral evolution. Radio observations can reveal jets, which are common from X-ray binaries. –Likewise, we need to determine whether the radio transients seen near the Galactic center have X-ray counterparts. Infrared observations can detect accreting companions. TeV instruments will soon have the baseline to identify transients.