We detected a correlation between optical and giant radio pulse emission from the Crab pulsar. Optical pulses coincident with the giant radio pulses were on average 3% brighter than those coincident with normal radio pulses. Combined with the lack of any other pulse profile changes, this result indicates that both the giant radio pulses and the increased optical emission are linked to an increase in the electron-positron plasma density.

No abstract

Many astronomical objects emit polarised light, which can give information both about their source mechanisms, and about (scattering) geometry in their source regions. To date (mostly) only the linearly polarised components of the emission have been observed in stellar sources. Observations have been constrained because of instrumental considerations to periods of excellent observing conditions, and to steady, slowly or periodically-varying sources. This leaves a whole range of interesting objects beyond the range of observation at present. The Galway Astronomical Stokes Polarimeter (GASP) has been developed to enable us to make observations on these very sources. GASP measures the four components of the Stokes Vector simultaneously over a broad wavelength range 400-800nm., with a time resolution of order microseconds given suitable detectors and a bright source -this is possible because the optical design contains no moving or modulating components. The initial design of GASP is presented and we include some preliminary observational results demonstrating that components of the Stokes vector can be measured to <1% in conditions of poor atmospheric stability. Issues of efficiency and stability are addressed. An analysis of suitable astronomical targets, demanding the unique properties of GASP, is also presented.

We have investigated both the temporal and spatial structure of the point spread function (PSF) produced by the Lick Observatory adaptive optics (AO) system using the FastSub readout mode of the IRCAL camera using short-exposure images with exposure times of 22ms at a frame rate of ∼ 20Hz suitable for "freezing" the compensation under typical Kband observing conditions. These short exposures are a useful diagnostic tool for determining the system performance and permit measurement of the instantaneous Strehl ratio. Data taken from a number of observing runs, spanning over four months, show the underlying morphology of the PSF to be very stable with instantaneous Strehl ratios varying from ∼ 20%-70% in NGS mode. Estimates of the instantaneous Strehl distribution have also been obtained from which we have determined the probability density function for the distribution of the instantaneous Strehl ratios.