Search for the infrared counterpart of the Bursting Pulsar - progress report

AAT observations:

The data were obtained on UT 1997 February 21, at the Cassegrain focus of the Anglo Australian Telescope, using the facility infrared camera IRIS, at a pixel scale of 0.24 arcsec. Twelve images were taken of the region covering the GROJ1744-28 counterpart candidate, each consisting of 30 coadds of 5s. The entire observation lasted about 30 minutes. Seeing was poor - 2 arcsec in the visible.

Data reduction:

The images were dark-subtracted, flatfielded and linearized by SLL. A median sky frame was formed by stacking all 12 images plus the 3 standard star observations, and this was subtracted from all the frames with no scaling (PRB). The 12 images were subsequently registered and mosaiced (in some cases with a DC offset and scaling factor applied) by PRB.

Preliminary results:

The resulting mosaic is shown below at 3 contrast levels, accompanied by the exposure map. The GIF files are at orginal pixel scale (with North at top, East at left). In this mosaic, no source is apparent at the position of the Blanco et al. K band image of 1996 Feb 8. However, the poor seeing and short exposure means that the limiting magnitude is slightly worse than the Blanco et al. image. Inspection of the individual frames yielded no source detection, either.
low contrast image higher contrast image
highest contrastexposure map

To be done:

  1. More careful sky subtraction (with scaling)
  2. More careful definition of bad pixels in each frame
  3. Sub-pixel registration
  4. Absolute flux calibration
However, these are unlikely to give a significant improvement in the final mosaic.
These images are currently proprietary, and may not be used or cited without the permission of Philip Blanco and/or Karl Glazebrook. Improved versions will be made public through the GROJ1744-28 WWW page as time permits.

PRB and KGB are grateful to Stuart Lumsden for assistance with the observing and data reduction, and to the AAT Service Observing Programme for the time.