Chandra's First Decade of Discovery

Session 11: The Galactic Center

Revelations in our own backyard: Chandra's unique Galactic center discoveries

Sera Markoff, Astronomical Institute “Anton Pannekoek”, University of Amsterdam

Before the launch of Chandra, our Galactic center supermassive black hole, Sgr A*, had never been positively identified outside the radio bands. A great deal has changed in the last decade, starting with the discovery that our own backyard harbors a very weak, yet clearly active, galactic nucleus. I will review how this revelation has been a boon for accretion studies around black holes in general, and has helped us place our own Galaxy in context with the AGN zoology. While the focus of my talk will be on this topic, I will also touch on how Chandra's exquisite resolution has unveiled active star formation, entirely new populations of faint sources and transients, as well as extreme gas dynamics and hints of prior, more typical AGN-like activity in our Galactic center.

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The Galactic Bulge Survey: finding eclipsing X-ray binaries and understanding the Galactic X-ray binary population

Peter Jonker, SRON & CfA
C. Bassa (Machester Univ), G. Nelemans (Nijmegen Univ) et al.

The Galactic Bulge Survey is a multi-wavelength project aimed at understanding the population of faint X-ray sources towards the Galactic center, though avoiding the Galactic plane itself to avoid the huge extinction and problems caused by crowding. In order to sample the populations sufficiently, the total survey area will be 12square degrees. It consists of 2ks-long Chandra observations and optical Blanco images down to r' = 24. Thus far, the optical data is complete and the Chandra data covering 8.4 square degrees have revealed ~1350 X-ray sources. For ~1000 sources we have discovered counterparts on our optical Blanco images. A fraction of ~20 per cent of these are expected to be interloper stars. The plethora of faint X-ray sources will be compared to detailed population models in order to constrain binary evolution models, especially the common envelope phase, by way of number counts. We are using optical to X-ray flux ratios, optical and X-ray colours and follow-up optical spectroscopy of the detected optical counterparts to classify all sources. We expect to find several quiescent and eclipsing neutron star and black hole LMXBs. These will be used for detailed neutron star and black hole mass measurements. Mass measuremetns are vital for studies of the neutron star equation of state and supernova modelling. Lastly, we will use the distribution of (quiescent) LMXBs to test if LMXB formation requires a kick imparted on the compact object or not as the apparent asymmetry in the Galactic distribution of LMXBs suggests. We will present the first results, and first surprises, of our optical and Chandra observations and the multi-wavelength follow-up of these Chandra X-ray discovered sources.

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Chandra Studies of Planets and Comets in the X-ray

Carey Lisse, Johns Hopkins University Applied Physics Laboratory
A. Bhardwaj (Vikram Sarabhai Space Centre), S. J. Wolk (CXC), D. J. Christian (CSUN), K. Dennerl (MPE), D. Bodewits (GSFC), T.H. Zurbuchen (UMich)

The discovery of high energy x-ray emission in 1996 from C/1996 B2 (Hyakutake) created a new class of solar system x-ray emitting objects [1]. Subsequent detections of the morphology, spectra, and time dependence of the x-rays from more than 20 comets have shown that the very soft (E < 1 keV) emission is due to a charge-exchange interaction between highly charged solar wind minor ions and the comet's extended neutral atmosphere [2,3]. Several other solar system objects are now known to shine in the X-ray, including Venus, Mars, the Moon, the Earth, Jupiter, and Saturn, with total power outputs on the MW - GW scale [4]. Like comets, the X-ray emission from the Earth's geo-corona, the Jovian aurora, and the Martian halo are all driven by charge exchange between highly charged minor (heavy) ions in the solar wind and gaseous neutral species in the bodies' atmosphere. The first soft X-ray observation of Earth's aurora by Chandra shows that it is highly variable, and the Jovian aurora is a fascinating puzzle that is just beginning to yield its secrets. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, and those from disks of Mars, Venus, and the Moon are mainly produced due to scattering of solar X-rays We present a summary of recent planetary and cometary observations by the Chandra, CHIPS, EUVE, ROSAT, Swift, and XMM spacecraft, in conjunction with solar wind measurements made by the ACE, IMP-8, SOHO, and TRACE spacecraft, in order to demonstrate the richness and utility of solar system x-ray emission.References[1] C.M. Lisse et al., Science 274, 205 (1996)[2] R. Wegmann and K. Dennerl, A&A 430, L33 (2005)[3] D. Bodewits et al., A&A 469, 1183 (2007)[4] A. Bhardwaj et al., PSS 55, 1135 - 1189 (2007)

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