S. Duscha

OPTIMA: A High Time Resolution Optical Photo-Polarimeter

A high-speed photo-polarimeter, “OPTIMA” short for Optical Pulsar Timing Analyzer, has been designed and developed in the group for gamma-ray astronomy of the Max-Planck-Institut fur Extraterrestrische Physik. This sensitive, portable detector is used to observe optical emissions of sources that radiate mainly at X- and gamma-ray energies, like pulsars and other highly variable compact sources. The single photon counting instrument is based on fiber fed avalanche photodiodes (APDs), a GPS timing receiver,a CCD camera for target acquisition and a stand-alone data acquisition and control system. Several configurations are available: for photometry a hexagonal bundle with seven channels and one fiber offset for sky background monitoring; for polarimetry a rotating polarization filter in front of the photometer or a newly developed 4-channel double Wollaston system; and for coarse spectroscopy a 4-colour prism spectrograph.

OPTIMA‐Burst: Observing GRB Afterglows and other Fast Transients with High Time Resolution

OPTIMA‐Burst is a high time resolution optical photo/polarimeter specifically developed for the study of GRB Afterglows. It combines a high‐speed single‐photon counting photo/polarimeter with accurate (4 μs) and absolute (GPS) tagging of photon arrival‐times, with a telescope with a quick automatic response to external Burst Triggers (GCN). Thus the instrument facilitates GRB afterglow photometry and polarimetry of early fast variability and flares. This allows unique insights into the physics of the ultra‐relativistic jets assumed in GRBs and their Afterglows. OPTIMA‐Burst was deployed for three months in 2006 on the 1.3 m Telescope of the Skinakas Observatory (Crete) proving the viability of the observation principle and of the instruments implementation. Observations of polarized and highly variable sources (e.g. Crab Pulsar, CVs) allowed the determination of sensitivity. In 2007 a second long‐duration campaign was performed, during which OPTIMA‐Burst observed a peculiar transient source showing unusually strong flaring activity on very short timescales. OPTIMA‐Bursts unique combination of quick response‐time and high time resolution proved to be very valuable in the discovery of this source.

High time resolution observations of Cataclysmic Variables with OPTIMA

The high‐speed photometer ‘OPTIMA’, short for Optical Pulsar Timing Analyzer, was used to record optical (450–950 nm) light curves of selected cataclysmic variables of type AM Her (Polars) with sub‐second temporal resolution. The objects RX J0704+62, RX J0953+14, and EK UMa were re‐observed several years after their discovery to provide up to date light curves with good statistics. The eclipsing binary DP Leo, which had been observed during 20 years previous to the OPTIMA measurements, was shown to have an orbital ephemeris with a quadratic term. For HU Aqr we have collected data over the years 1999 to 2007. HU Aqr evolved in luminosity from a high state in 2000 to a low state that persists since 2001. We detected variability in HU Aqr in the form of optical flashes with timescales of seconds.