Galactic Center and Sgr A*
I helped write a “Chandra X-ray Visionary Project (XVP)” proposal to observe Sgr A*, the supermassive black hole at the center of our Galaxy, for 3 Msec using the Chandra–HETGS. The below image is our summed observations, aligning the “0th order images” in the center, and aligning along the gratings dispersion arms in the outer region.
The collaboration web site is at: www.sgra-star.com. Our science results can be found in:
- The X-ray Flux Distribution of Sagitarius A* as Seen by Chandra
- A Chandra/HETGS Census of X-ray Variability from Sgr A* during 2012
- Dissecting X-ray-Emitting Gas Around the Center of Our Galaxy
- Chandra/HETGS Observations of the Brightest Flare Seen from Sgr A*
Spectroscopy of Black Hole Systems
One of the main goals of observations of black hole systems is to try and determine the mass and spin of the black hole, and to search for some of the exotic space/time effects of General Relativity. Such searches, however, are complicated by the other astrophysical effects occurring in these systems: coronae, jets, winds from the accretion disk, winds from the companion star, foreground dust. High resolution spectroscopy (e.g., Chandra-HETGS), in combination with broad band spectroscopy (e.g., NuSTAR) is allowing us to disentangle these effects.
One of the main goals of observations of black hole systems is to try and determine the mass and spin of the black hole, and to search for some of the exotic space/time effects of General Relativity. Such searches, however, are complicated by the other astrophysical effects occurring in these systems: coronae, jets, winds from the accretion disk, winds from the companion star, foreground dust. High resolution spectroscopy (e.g., Chandra-HETGS), in combination with broad band spectroscopy (e.g., NuSTAR) is allowing us to disentangle these effects.
- Leveraging high-resolution spectra to understand black hole spectra
- Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system
- The Complex Accretion Geometry of GX 339-4 as Seen by NuSTAR and Swift
- Long term variability of Cygnus X-1. VII. Orbital variability of the focused wind
- A Chandra-HETG View of MCG +8-11-11
Neutron Star Systems
Neutron stars can be quite different from black hole systems owing to the fact that they have a surface! How does this affect the accretion properties? Does the thermal emission from a cooling neutron star reveal information about the equation of state of nuclear matter? How do neutron stars transit between quiescent states and active X-ray pulsar states? Some of my neutron star work can be found in:
- A Hard X-ray Spectral Cutoff in Centaurus X-4
- The Youngest Known X-ray Binary: Circinus X-1 and its Natal Supernova Remnant
- X-ray and Near-infrared Observations of the Obscured Accreting Pulsar IGR J18179–1621
- A Chandra Observation of the Bursting Millisecond X-ray Pulsar IGR J17511–3057
- Implications of X-ray Line Variations for 4U 1822–371
- A Further Drop into Quescence by the Eclipsing Neutron Star 4U 2129+47
On the left is an actual Chandra movie of the quiescent neutron star, 4U 2129+47. The disappearance is due to a periodic (every 5.3 hours) eclipse by its unseen optical companion. In fact, it is likely that this system is in fact a triple system, with the observed optical star in a several hundred day orbit about the 5.3 hour binary. On the right is a theoretical model, based upon RXTE data, of the optical companion, accretion disk, and corona in the 4U 1822–371 neutron star system. This is what 4U 2129+47 likely looked like when it was in an X-ray active state.