The Science!

OGRESS is designed to fill a whole in the capabilities of the Chandra and XMM-Newton space telescopes. Chandra (NASA) and XMM-Newton (ESA) are terrific instruments which have high spatial resolution (providing great pictures) and high spectral resolution when observing point sources. When observing diffuse sources, however, their spectral resolution degrades according to the size of the object.

The picture below demonstrates what happens when Chandra observes a non-point source. The image of the target is diffracted into a spectrum, and the resulting spectral resolution is inversely proportional to the size of the target.

The biggest objects on the sky are too big to even fit into Chandra's and XMM's fields of view.

The Cygnus Loop supernova remnant is one of these large objects. It is so big that Chandra must rely on the (low) energy resolution of its detectors to produce a spectrum. The image below shows Cygnus, as seen by the ROSAT satellite, which made the first all-sky x-ray survey. The boxes on the right side of the image represent Chandra's field of view.

Because the Cygnus Loop is so large, all x-ray spectra thus far have been low resolution. A higher resolution spectrum would provide much more information on the elemental abundances of the ejecta, as well as tighter constraints on physical parameters such as temperature, ionization state, shock velocity, and more.