Monday, March 3, 2014

Optical Pulses Detected by BVIT of pulsar PSR B0540-69

In January the first successful SALT BVIT observations of  rapid optical pulsations from a pulsar were reported by Sarah Buchner (HartRAO) and her collaborators Andy Shearer (National University of Ireland, Galway) and Darragh O'Donoghue (SALT). Andy Shearer reports:

The Large Magellanic Cloud pulsar, PSR B0540-69, on the basis of its age and position within its plerionic supernova remnant, is often referred to as the Crab pulsar twin. Despite this similarity it has not been as extensively studied as the Crab pulsar. It is about 100 times fainter than the Crab, which in part explains why it hasn’t been extensively observed. To rectify this a large telescope and fast detector is needed - BVIT and SALT. Below left is a BVIT image, showing the pulsar in an extended region of nebulosity. Photometry was performed relative to other stars circled in the image. For comparison, the Hubble Space Telescope (HST) image of the same region is shown on the right.

Time resolved optical observations have been taken in the past on the HST and 4m ESO and AAT telescopes. Using BVIT and SALT, PSR B0540-69 was observed over 4 nights in late December 2013 by SALT Astronomer, Paul Kotze. Observing conditions were variable during this time, but for short periods of about 20 minutes it was possible to observe the pulsar. Even in these short intervals the signal from the pulsar was clearly visible - see plots below taken from one twenty minute observation. From these observations we have established the viability of BVIT/SALT combination as optical pulsar observatory.

BVIT optical light curve of PSR B0540-69, folded on the 50.7 millisecond spin period

The optical power spectrum of PSR B0540-69

Detailed observations of Southern Hemisphere pulsars, such as Vela, will now be possible - effectively tripling the number of pulsars which can be studied optically in detail. From these observations we will be able to accurately measure the pulse shape, the delay between the optical emission and emission at other wavelengths - notably X-ray and radio. This analysis in turn can be used to restrict the models for the optical and high energy pulsar emission.

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