High Time Resolution instrumentation at X-ray wavelengths has provided key results for over 50 years. Could you comment on the highlights of High Time Resolution X-ray astronomy?

Discovery of X-ray pulsations (periods of a few seconds) in the early 70s by the Uhuru satellite demonstrated in the clearest way possible that luminous X-ray sources in our Galaxy were accreting neutron stars. 

Then EXOSAT in the 80s discovered quasi-periodic oscillations (QPOs) with much faster frequencies (tens to hundreds of Hertz) due to the interaction of accreting matter with the intense magnetic field of even more rapidly spinning neutron stars. This was taken even further by RXTE in the 90s with the discovering of millisecond pulsars (i.e. spinning faster than 500 times per second!), long predicted as the natural end result of the accretion process which spins up the neutron star.

And I would also highlight the discovery in the 70s of X-ray bursts associated with accreting neutron stars.  These bursts rise to maximum within a second or two, then decay exponentially over the next minute or so, and are due to thermonuclear explosions in the thin accretion layer (which is hydrogen) on the surface of the neutron star.  They repeat on timescales of hours to days.

What has been the main breakthrough in High Time Resolution technology that has allowed us to perform High Time Resolution at other wavelengths?

In X-rays, fortunately the technology of their detection (proportional counters, essentially a variant of well-known laboratory geiger counters) makes it straightforward to achieve high time resolution (of milliseconds or better), but the limitation in the discovery of the most rapid variations was simply having a large enough collecting area (i.e. big enough telescope) in space.  So the major breakthroughs came with the very large collecting area of the RXTE proportional counters in the 90s.

At optical wavelengths, simple photomultiplier tubes have been around since the 1940s, but they were just flux collectors and had no imaging capability.  Imaging was originally done photographically, so the time resolution was very poor.  That has been improved with micro-channel plate technology, but its sensitivity is no better than phototubes.  Now that virtually all imaging is done with CCDs (which have very high sensitivity, approaching 100%!), their time resolution was unfortunately quite poor (tens of seconds to minutes) because of the time needed for the electronics to read out the image!  That has improved considerably in the last decade with advances in electronics.

Throughout your scientific career you have witnessed the birth of High Energy Astrophysics along with new exciting developments in "classical" optical and near-infrared instrumentation. How does technology determine our vision of the Universe?

The advances through the forty years I have been a research astronomer have all been a result of the huge technology gains that have taken place since the Second World War, particularly in the space arena, where many wavelengths (X-ray, UV, large sections of IR) had been completely inaccessible from the ground.  But ground-based astronomy has been transformed by the invention of the CCD, which is ~50 times more sensitive than photographic film.   That meant the 80s saw a huge step forward just by changing the detector you were using on your telescope - it was the same gain as trebling the aperture of your telescope with the old technology, so our "vision" of the Universe was a dramatically new one because of this step-change in capability.

What are the prospects for future high-time resolution detectors?

One of the most exciting prospects for ground-based optical and infra-red astronomy is the exploitation of exotic new materials discovered by solid-state physicists, such as "STJs", or superconducting tunnel-junction detectors.  When cooled to extremely low temperatures (a tiny fraction of a degree above absolute zero!) these detectors are not only extremely sensitive detectors of single photons, but they are also capable of determining the energy (i.e. wavelength or colour) of that photon at the same time.  Combined with high time resolution, these have the potential for revolutionising observational astronomy at a wide range of wavelengths.

 Annia Domènech