Moving up in energy to the gamma-ray band apparently simplifies a number of problems in the search for sub micro arcsecond resolution. The proposed system is very long (millions of km) but the fabrication of the optics would be almost trivial and there is no need for critical alignment of the individual components. Only the pointing of the telescope as a whole is critical and it is suggested that the requirements of the pointing determination system are well matched to techniques using radio measurements, while the associated active control seems to be possible with existing technology.
Compared with proposals for achieving micro-arcsecond resolution at X-ray energies using interferometry, the approach suggested here has the disadvantage that it only operates over a narrow energy band at any one time. On the other hand, the optics are simple and are capable of concentrating the flux from a very large aperture onto a detector area 104-107 times smaller in area and so the sensitivity can be extremely good despite the small bandwidth. Furthermore, in the gamma-ray band micro arcsecond resolution can be obtained with modest diameter. For those objects which are gamma-ray sources as well as X-ray sources, the approach seems to be very promising.
Acknowledgements
The author is grateful for helpful comments and suggestions from J. Bar-Sever (JPL), J. Brown (University of Glasgow), N. Gehrels (GSFC) and colleagues at both the University of Birmingham and CESR, Toulouse.
Copyright ESO 2001